////
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    contributor license agreements. See the NOTICE file distributed with
    this work for additional information regarding copyright ownership.
    The ASF licenses this file to You under the Apache License, Version 2.0
    (the "License"); you may not use this file except in compliance with
    the License. You may obtain a copy of the License at

        https://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
////
= Appenders
Ralph Goers; Gary Gregory; Nick Williams; Matt Sicker

Appenders are responsible for delivering LogEvents to their destination.
Every Appender must implement the
link:../log4j-core/apidocs/org/apache/logging/log4j/core/Appender.html[`Appender`]
interface. Most Appenders will extend
link:../log4j-core/apidocs/org/apache/logging/log4j/core/appender/AbstractAppender.html[`AbstractAppender`]
which adds
link:../log4j-core/apidocs/org/apache/logging/log4j/core/LifeCycle.html[`Lifecycle`]
and
link:../log4j-core/apidocs/org/apache/logging/log4j/core/filter/Filterable.html[`Filterable`]
support. `Lifecycle` allows components to finish initialization after
configuration has completed and to perform cleanup during shutdown.
`Filterable` allows the component to have `Filter`s attached to it which are
evaluated during event processing.

Appenders usually are only responsible for writing the event data to the
target destination. In most cases they delegate responsibility for
formatting the event to a link:layouts.html[layout]. Some appenders wrap
other appenders so that they can modify the `LogEvent`, handle a failure
in an `Appender`, route the event to a subordinate `Appender` based on
advanced `Filter` criteria or provide similar functionality that does not
directly format the event for viewing.

Appenders always have a name so that they can be referenced from
Loggers.

In the tables below, the "Type" column corresponds to the Java type
expected. For non-JDK classes, these should usually be in
link:../log4j-core/apidocs/index.html[Log4j Core] unless otherwise
noted.

[#AsyncAppender]
== AsyncAppender

The AsyncAppender accepts references to other Appenders and causes
LogEvents to be written to them on a separate Thread. Note that
exceptions while writing to those Appenders will be hidden from the
application. The AsyncAppender should be configured after the appenders
it references to allow it to shut down properly.

By default, AsyncAppender uses
https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ArrayBlockingQueue.html[`java.util.concurrent.ArrayBlockingQueue`]
which does not require any external libraries. Note that multi-threaded
applications should exercise care when using this appender as such: the
blocking queue is susceptible to lock contention and our
link:../performance.html#asyncLogging[tests showed] performance may
become worse when more threads are logging concurrently. Consider using
link:async.html[lock-free Async Loggers] for optimal performance.

.AsyncAppender Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|AppenderRef |String |The name of the Appenders to invoke
asynchronously. Multiple AppenderRef elements can be configured.

|blocking |boolean |If true, the appender will wait until there are free
slots in the queue. If false, the event will be written to the error
appender if the queue is full. The default is true.

|shutdownTimeout |integer |How many milliseconds the Appender should
wait to flush outstanding log events in the queue on shutdown. The
default is zero which means to wait forever.

|bufferSize |integer a|
Specifies the maximum number of events that can be queued. The default
is 1024. Note that when using a disruptor-style `BlockingQueue`, this
buffer size must be a power of 2.

When the application is logging faster than the underlying appender can
keep up with for a long enough time to fill up the queue, the behaviour
is determined by the
link:../log4j-core/apidocs/org/apache/logging/log4j/core/async/AsyncQueueFullPolicy.html[`AsyncQueueFullPolicy`].

|errorRef |String |The name of the Appender to invoke if none of the
appenders can be called, either due to errors in the appenders or
because the queue is full. If not specified then errors will be ignored.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|name |String |The name of the Appender.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|includeLocation |boolean |Extracting location is an expensive operation
(it can make logging 5 - 20 times slower). To improve performance,
location is not included by default when adding a log event to the
queue. You can change this by setting includeLocation="true".

|BlockingQueueFactory |BlockingQueueFactory |This element overrides what
type of `BlockingQueue` to use. See link:#BlockingQueueFactory[below
documentation] for more details.
|=======================================================================

There are also a few system properties that can be used to maintain
application throughput even when the underlying appender cannot keep up
with the logging rate and the queue is filling up. See the details for
system properties
link:configuration.html#log4j2.AsyncQueueFullPolicy[`log4j2.AsyncQueueFullPolicy`
and `log4j2.DiscardThreshold`].

A typical AsyncAppender configuration might look like:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <File name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </File>
    <Async name="Async">
      <AppenderRef ref="MyFile"/>
    </Async>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Async"/>
    </Root>
  </Loggers>
</Configuration>
----

[[BlockingQueueFactory]] Starting in Log4j 2.7, a custom implementation
of `BlockingQueue` or `TransferQueue` can be specified using a
link:../log4j-core/apidocs/org/apache/logging/log4j/core/async/BlockingQueueFactory.html[`BlockingQueueFactory`]
plugin. To override the default `BlockingQueueFactory`, specify the
plugin inside an `<Async/>` element like so:

[source,xml]
----
<Configuration name="LinkedTransferQueueExample">
  <Appenders>
    <List name="List"/>
    <Async name="Async" bufferSize="262144">
      <AppenderRef ref="List"/>
      <LinkedTransferQueue/>
    </Async>
  </Appenders>
  <Loggers>
    <Root>
      <AppenderRef ref="Async"/>
    </Root>
  </Loggers>
</Configuration>
----

Log4j ships with the following implementations:

.BlockingQueueFactory Implementations
[cols=",",options="header",]
|=======================================================================
|Plugin Name |Description
|ArrayBlockingQueue |This is the default implementation that uses
https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ArrayBlockingQueue.html[`ArrayBlockingQueue`].

|DisruptorBlockingQueue |This uses the
https://github.com/conversant/disruptor[Conversant Disruptor]
implementation of `BlockingQueue`. This plugin takes a single optional
attribute, `spinPolicy`, which corresponds to the `SpinPolicy` enum.

|JCToolsBlockingQueue |This uses
https://jctools.github.io/JCTools/[JCTools], specifically the MPSC
bounded lock-free queue.

|LinkedTransferQueue |This uses the new in Java 7 implementation
https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedTransferQueue.html[`LinkedTransferQueue`].
Note that this queue does not use the `bufferSize` configuration
attribute from AsyncAppender as `LinkedTransferQueue` does not support a
maximum capacity.
|=======================================================================

[#CassandraAppender]
== CassandraAppender

The CassandraAppender writes its output to an
https://cassandra.apache.org/[Apache Cassandra] database. A keyspace and
table must be configured ahead of time, and the columns of that table
are mapped in a configuration file. Each column can specify either a
link:layouts.html[StringLayout] (e.g., a
link:layouts.html#PatternLayout[PatternLayout]) along with an optional
conversion type, or only a conversion type for
`org.apache.logging.log4j.spi.ThreadContextMap` or
`org.apache.logging.log4j.spi.ThreadContextStack` to store the
link:thread-context.html[MDC or NDC] in a map or list column
respectively. A conversion type compatible with `java.util.Date` will
use the log event timestamp converted to that type (e.g., use
`java.util.Date` to fill a `timestamp` column type in Cassandra).

.CassandraAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|batched |boolean |Whether or not to use batch statements to write log
messages to Cassandra. By default, this is `false`.

|batchType
|http://docs.datastax.com/en/drivers/java/3.0/com/datastax/driver/core/BatchStatement.Type.html[`BatchStatement.Type`]
|The batch type to use when using batched writes. By default, this is
`LOGGED`.

|bufferSize |int |The number of log messages to buffer or batch before
writing. By default, no buffering is done.

|clusterName |String |The name of the Cassandra cluster to connect to.

|columns |ColumnMapping[] |A list of column mapping configurations. Each
column must specify a column name. Each column can have a conversion
type specified by its fully qualified class name. By default, the
conversion type is `String`. If the configured type is
assignment-compatible with
link:../log4j-api/apidocs/org/apache/logging/log4j/util/ReadOnlyStringMap.html[`ReadOnlyStringMap`]
/
link:../log4j-api/apidocs/org/apache/logging/log4j/spi/ThreadContextMap.html[`ThreadContextMap`]
or
link:../log4j-api/apidocs/org/apache/logging/log4j/spi/ThreadContextStack.html[`ThreadContextStack`],
then that column will be populated with the MDC or NDC respectively. If
the configured type is assignment-compatible with `java.util.Date`, then
the log timestamp will be converted to that configured date type. If a
`literal` attribute is given, then its value will be used as is in the
`INSERT` query without any escaping. Otherwise, the layout or pattern
specified will be converted into the configured type and stored in that
column.

|contactPoints |SocketAddress[] |A list of hosts and ports of Cassandra
nodes to connect to. These must be valid hostnames or IP addresses. By
default, if a port is not specified for a host or it is set to 0, then
the default Cassandra port of 9042 will be used. By default,
`localhost:9042` will be used.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|keyspace |String |The name of the keyspace containing the table that
log messages will be written to.

|name |String |The name of the Appender.

|password |String |The password to use (along with the username) to
connect to Cassandra.

|table |String |The name of the table to write log messages to.

|useClockForTimestampGenerator |boolean |Whether or not to use the
configured `org.apache.logging.log4j.core.time.Clock` as a
http://docs.datastax.com/en/drivers/java/3.0/com/datastax/driver/core/TimestampGenerator.html[`TimestampGenerator`].
By default, this is `false`.

|username |String |The username to use to connect to Cassandra. By
default, no username or password is used.

|useTls |boolean |Whether or not to use TLS/SSL to connect to Cassandra.
This is `false` by default.
|=======================================================================

Here is an example CassandraAppender configuration:

[source,xml]
----
<Configuration name="CassandraAppenderTest">
  <Appenders>
    <Cassandra name="Cassandra" clusterName="Test Cluster" keyspace="test" table="logs" bufferSize="10" batched="true">
      <SocketAddress host="localhost" port="9042"/>
      <ColumnMapping name="id" pattern="%uuid{TIME}" type="java.util.UUID"/>
      <ColumnMapping name="timeid" literal="now()"/>
      <ColumnMapping name="message" pattern="%message"/>
      <ColumnMapping name="level" pattern="%level"/>
      <ColumnMapping name="marker" pattern="%marker"/>
      <ColumnMapping name="logger" pattern="%logger"/>
      <ColumnMapping name="timestamp" type="java.util.Date"/>
      <ColumnMapping name="mdc" type="org.apache.logging.log4j.spi.ThreadContextMap"/>
      <ColumnMapping name="ndc" type="org.apache.logging.log4j.spi.ThreadContextStack"/>
    </Cassandra>
  </Appenders>
  <Loggers>
    <Logger name="org.apache.logging.log4j.cassandra" level="DEBUG">
      <AppenderRef ref="Cassandra"/>
    </Logger>
    <Root level="ERROR"/>
  </Loggers>
</Configuration>
----

This example configuration uses the following table schema:

[source,sql]
----
CREATE TABLE logs (
    id timeuuid PRIMARY KEY,
    timeid timeuuid,
    message text,
    level text,
    marker text,
    logger text,
    timestamp timestamp,
    mdc map<text,text>,
    ndc list<text>
);
----

[#ConsoleAppender]
== ConsoleAppender

As one might expect, the ConsoleAppender writes its output to either
System.out or System.err with System.out being the default target. A
Layout must be provided to format the LogEvent.

.ConsoleAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|layout |Layout |The Layout to use to format the LogEvent. If no layout
is supplied the default pattern layout of "%m%n" will be used.

|follow |boolean |Identifies whether the appender honors reassignments
of System.out or System.err via System.setOut or System.setErr made
after configuration. Note that the follow attribute cannot be used with
Jansi on Windows. Cannot be used with `direct`.

|direct |boolean |Write directly to `java.io.FileDescriptor` and bypass
`java.lang.System.out/.err`. Can give up to 10x performance boost when
the output is redirected to file or other process. Cannot be used with
Jansi on Windows. Cannot be used with `follow`. Output will not respect
`java.lang.System.setOut()/.setErr()` and may get intertwined with other
output to `java.lang.System.out/.err` in a multi-threaded application.
_New since 2.6.2. Be aware that this is a new addition, and it has only
been tested with Oracle JVM on Linux and Windows so far._

|name |String |The name of the Appender.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|target |String |Either "SYSTEM_OUT" or "SYSTEM_ERR". The default is
"SYSTEM_OUT".
|=======================================================================

A typical Console configuration might look like:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="STDOUT"/>
    </Root>
  </Loggers>
</Configuration>
----

[#FailoverAppender]
== FailoverAppender

The FailoverAppender wraps a set of appenders. If the primary Appender
fails the secondary appenders will be tried in order until one succeeds
or there are no more secondaries to try.

.FailoverAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|primary |String |The name of the primary Appender to use.

|failovers |String[] |The names of the secondary Appenders to use.

|name |String |The name of the Appender.

|retryIntervalSeconds |integer |The number of seconds that should pass
before retrying the primary Appender. The default is 60.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead.

|target |String |Either "SYSTEM_OUT" or "SYSTEM_ERR". The default is
"SYSTEM_ERR".
|=======================================================================

A Failover configuration might look like:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log" filePattern="logs/app-%d{MM-dd-yyyy}.log.gz"
                 ignoreExceptions="false">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <TimeBasedTriggeringPolicy />
    </RollingFile>
    <Console name="STDOUT" target="SYSTEM_OUT" ignoreExceptions="false">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Failover name="Failover" primary="RollingFile">
      <Failovers>
        <AppenderRef ref="Console"/>
      </Failovers>
    </Failover>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Failover"/>
    </Root>
  </Loggers>
</Configuration>
----

[#FileAppender]
== FileAppender

The FileAppender is an OutputStreamAppender that writes to the File
named in the fileName parameter. The FileAppender uses a FileManager
(which extends OutputStreamManager) to actually perform the file I/O.
While FileAppenders from different Configurations cannot be shared, the
FileManagers can be if the Manager is accessible. For example, two web
applications in a servlet container can have their own configuration and
safely write to the same file if Log4j is in a ClassLoader that is
common to both of them.

.FileAppender Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|append |boolean |When true - the default, records will be appended to
the end of the file. When set to false, the file will be cleared before
new records are written.

|bufferedIO |boolean |When true - the default, records will be written
to a buffer and the data will be written to disk when the buffer is full
or, if immediateFlush is set, when the record is written. File locking
cannot be used with bufferedIO. Performance tests have shown that using
buffered I/O significantly improves performance, even if immediateFlush
is enabled.

|bufferSize |int |When bufferedIO is true, this is the buffer size, the
default is 8192 bytes.

|createOnDemand |boolean |The appender creates the file on-demand. The
appender only creates the file when a log event passes all filters and
is routed to this appender. Defaults to false.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|fileName |String |The name of the file to write to. If the file, or any
of its parent directories, do not exist, they will be created.

|immediateFlush |boolean a|
When set to true - the default, each write will be followed by a flush.
This will guarantee that the data is passed to the operating system for writing;
it does not guarantee that the data is actually written to a physical device
such as a disk drive.

Note that if this flag is set to false, and the logging activity is sparse,
there may be an indefinite delay in the data eventually making it to the
operating system, because it is held up in a buffer.
This can cause surprising effects such as the logs not
appearing in the tail output of a file immediately after writing to the log.

Flushing after every write is only useful when using this appender with
synchronous loggers. Asynchronous loggers and appenders will
automatically flush at the end of a batch of events, even if
immediateFlush is set to false. This also guarantees the data is passed
to the operating system but is more efficient.

|layout |Layout |The Layout to use to format the LogEvent. If no layout
is supplied the default pattern layout of "%m%n" will be used.

|locking |boolean |When set to true, I/O operations will occur only
while the file lock is held allowing FileAppenders in multiple JVMs and
potentially multiple hosts to write to the same file simultaneously.
This will significantly impact performance so should be used carefully.
Furthermore, on many systems the file lock is "advisory" meaning that
other applications can perform operations on the file without acquiring
a lock. The default value is false.

|name |String |The name of the Appender.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|filePermissions |String a|
File attribute permissions in POSIX format to apply whenever the file is
created.

Underlying files system shall support
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/PosixFileAttributeView.html[POSIX]
file attribute view.

Examples: `rw-------` or `rw-rw-rw-` etc...

|fileOwner |String a|
File owner to define whenever the file is created.

Changing file's owner may be restricted for security reason and
Operation not permitted IOException thrown. Only processes with an
effective user ID equal to the user ID of the file or with appropriate
privileges may change the ownership of a file if
http://www.gnu.org/software/libc/manual/html_node/Options-for-Files.html[_POSIX_CHOWN_RESTRICTED]
is in effect for path.

Underlying files system shall support file
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/FileOwnerAttributeView.html[owner]
attribute view.

|fileGroup |String a|
File group to define whenever the file is created.

Underlying files system shall support
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/PosixFileAttributeView.html[POSIX]
file attribute view.

|=======================================================================

Here is a sample File configuration:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <File name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </File>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="MyFile"/>
    </Root>
  </Loggers>
</Configuration>
----

[#FlumeAppender]
== FlumeAppender

_This is an optional component supplied in a separate jar._

http://flume.apache.org/index.html[Apache Flume] is a distributed,
reliable, and available system for efficiently collecting, aggregating,
and moving large amounts of log data from many different sources to a
centralized data store. The FlumeAppender takes LogEvents and sends them
to a Flume agent as serialized Avro events for consumption.

The Flume Appender supports three modes of operation.

1.  It can act as a remote Flume client which sends Flume events via
Avro to a Flume Agent configured with an Avro Source.
2.  It can act as an embedded Flume Agent where Flume events pass
directly into Flume for processing.
3.  It can persist events to a local BerkeleyDB data store and then
asynchronously send the events to Flume, similar to the embedded Flume
Agent but without most of the Flume dependencies.

Usage as an embedded agent will cause the messages to be directly passed
to the Flume Channel and then control will be immediately returned to
the application. All interaction with remote agents will occur
asynchronously. Setting the "type" attribute to "Embedded" will force
the use of the embedded agent. In addition, configuring agent properties
in the appender configuration will also cause the embedded agent to be
used.

.FlumeAppender Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|agents |Agent[] |An array of Agents to which the logging events should
be sent. If more than one agent is specified the first Agent will be the
primary and subsequent Agents will be used in the order specified as
secondaries should the primary Agent fail. Each Agent definition
supplies the Agents host and port. The specification of agents and
properties are mutually exclusive. If both are configured an error will
result.

|agentRetries |integer |The number of times the agent should be retried
before failing to a secondary. This parameter is ignored when
type="persistent" is specified (agents are tried once before failing to
the next).

|batchSize |integer |Specifies the number of events that should be sent
as a batch. The default is 1. _This parameter only applies to the Flume
Appender._

|compress |boolean |When set to true the message body will be compressed
using gzip

|connectTimeoutMillis |integer |The number of milliseconds Flume will
wait before timing out the connection.

|dataDir |String |Directory where the Flume write ahead log should be
written. Valid only when embedded is set to true and Agent elements are
used instead of Property elements.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|eventPrefix |String |The character string to prepend to each event
attribute in order to distinguish it from MDC attributes. The default is
an empty string.

|flumeEventFactory |FlumeEventFactory |Factory that generates the Flume
events from Log4j events. The default factory is the FlumeAvroAppender
itself.

|layout |Layout |The Layout to use to format the LogEvent. If no layout
is specified RFC5424Layout will be used.

|lockTimeoutRetries |integer |The number of times to retry if a
LockConflictException occurs while writing to Berkeley DB. The default
is 5.

|maxDelayMillis |integer |The maximum number of milliseconds to wait for
batchSize events before publishing the batch.

|mdcExcludes |String |A comma separated list of mdc keys that should be
excluded from the FlumeEvent. This is mutually exclusive with the
mdcIncludes attribute.

|mdcIncludes |String |A comma separated list of mdc keys that should be
included in the FlumeEvent. Any keys in the MDC not found in the list
will be excluded. This option is mutually exclusive with the mdcExcludes
attribute.

|mdcRequired |String |A comma separated list of mdc keys that must be
present in the MDC. If a key is not present a LoggingException will be
thrown.

|mdcPrefix |String |A string that should be prepended to each MDC key in
order to distinguish it from event attributes. The default string is
"mdc:".

|name |String |The name of the Appender.

|properties |Property[] a|
One or more Property elements that are used to configure the Flume
Agent. The properties must be configured without the agent name (the
appender name is used for this) and no sources can be configured.
Interceptors can be specified for the source using
"sources.log4j-source.interceptors". All other Flume configuration
properties are allowed. Specifying both Agent and Property elements will
result in an error.

When used to configure in Persistent mode the valid properties are:

1.  "keyProvider" to specify the name of the plugin to provide the
secret key for encryption.

|requestTimeoutMillis |integer |The number of milliseconds Flume will
wait before timing out the request.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|type |enumeration |One of "Avro", "Embedded", or "Persistent" to
indicate which variation of the Appender is desired.
|=======================================================================

A sample FlumeAppender configuration that is configured with a primary
and a secondary agent, compresses the body, and formats the body using
the RFC5424Layout:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp">
  <Appenders>
    <Flume name="eventLogger" compress="true">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="eventLogger"/>
    </Root>
  </Loggers>
</Configuration>
----

A sample FlumeAppender configuration that is configured with a primary
and a secondary agent, compresses the body, formats the body using the
RFC5424Layout, and persists encrypted events to disk:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Flume name="eventLogger" compress="true" type="persistent" dataDir="./logData">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
      <Property name="keyProvider">MySecretProvider</Property>
    </Flume>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="eventLogger"/>
    </Root>
  </Loggers>
</Configuration>
----

A sample FlumeAppender configuration that is configured with a primary
and a secondary agent, compresses the body, formats the body using
RFC5424Layout and passes the events to an embedded Flume Agent.

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Flume name="eventLogger" compress="true" type="Embedded">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Console name="STDOUT">
      <PatternLayout pattern="%d [%p] %c %m%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Logger name="EventLogger" level="info">
      <AppenderRef ref="eventLogger"/>
    </Logger>
    <Root level="warn">
      <AppenderRef ref="STDOUT"/>
    </Root>
  </Loggers>
</Configuration>
----

A sample FlumeAppender configuration that is configured with a primary
and a secondary agent using Flume configuration properties, compresses
the body, formats the body using RFC5424Layout and passes the events to
an embedded Flume Agent.

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error" name="MyApp" packages="">
  <Appenders>
    <Flume name="eventLogger" compress="true" type="Embedded">
      <Property name="channels">file</Property>
      <Property name="channels.file.type">file</Property>
      <Property name="channels.file.checkpointDir">target/file-channel/checkpoint</Property>
      <Property name="channels.file.dataDirs">target/file-channel/data</Property>
      <Property name="sinks">agent1 agent2</Property>
      <Property name="sinks.agent1.channel">file</Property>
      <Property name="sinks.agent1.type">avro</Property>
      <Property name="sinks.agent1.hostname">192.168.10.101</Property>
      <Property name="sinks.agent1.port">8800</Property>
      <Property name="sinks.agent1.batch-size">100</Property>
      <Property name="sinks.agent2.channel">file</Property>
      <Property name="sinks.agent2.type">avro</Property>
      <Property name="sinks.agent2.hostname">192.168.10.102</Property>
      <Property name="sinks.agent2.port">8800</Property>
      <Property name="sinks.agent2.batch-size">100</Property>
      <Property name="sinkgroups">group1</Property>
      <Property name="sinkgroups.group1.sinks">agent1 agent2</Property>
      <Property name="sinkgroups.group1.processor.type">failover</Property>
      <Property name="sinkgroups.group1.processor.priority.agent1">10</Property>
      <Property name="sinkgroups.group1.processor.priority.agent2">5</Property>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Console name="STDOUT">
      <PatternLayout pattern="%d [%p] %c %m%n"/>
    </Console>
  </Appenders>
  <Loggers>
    <Logger name="EventLogger" level="info">
      <AppenderRef ref="eventLogger"/>
    </Logger>
    <Root level="warn">
      <AppenderRef ref="STDOUT"/>
    </Root>
  </Loggers>
</Configuration>
----

[#JDBCAppender]
== JDBCAppender

As of Log4j 2.11.0, JDBC support has moved from the existing module
`log4j-core` to the new module `log4j-jdbc`.

The JDBCAppender writes log events to a relational database table using
standard JDBC. It can be configured to obtain JDBC connections using a
JNDI `DataSource` or a custom factory method. Whichever approach you
take, it *_must_* be backed by a connection pool. Otherwise, logging
performance will suffer greatly. If batch statements are supported by
the configured JDBC driver and a `bufferSize` is configured to be a
positive number, then log events will be batched. Note that as of Log4j
2.8, there are two ways to configure log event to column mappings: the
original `ColumnConfig` style that only allows strings and timestamps,
and the new `ColumnMapping` plugin that uses Log4j's built-in type
conversion to allow for more data types (this is the same plugin as in
the <<CassandraAppender>>).

To get off the ground quickly during development, an alternative to
using a connection source based on JNDI is to use the non-pooling
`DriverManager` connection source. This connection source uses a JDBC
connection string, a user name, and a password. Optionally, you can also
use properties.

.JDBCAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |_Required._ The name of the Appender.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|bufferSize |int |If an integer greater than 0, this causes the appender
to buffer log events and flush whenever the buffer reaches this size.

|connectionSource |ConnectionSource |_Required._ The connections source
from which database connections should be retrieved.

|tableName |String |_Required._ The name of the database table to insert
log events into.

|columnConfigs |ColumnConfig[] |_Required (and/or columnMappings)._
Information about the columns that log event data should be inserted
into and how to insert that data. This is represented with multiple
`<Column>` elements.

|columnMappings |ColumnMapping[] |_Required (and/or columnConfigs)._ A
list of column mapping configurations. Each column must specify a column
name. Each column can have a conversion type specified by its fully
qualified class name. By default, the conversion type is `String`. If
the configured type is assignment-compatible with
link:../log4j-api/apidocs/org/apache/logging/log4j/util/ReadOnlyStringMap.html[`ReadOnlyStringMap`]
/
link:../log4j-api/apidocs/org/apache/logging/log4j/spi/ThreadContextMap.html[`ThreadContextMap`]
or
link:../log4j-api/apidocs/org/apache/logging/log4j/spi/ThreadContextStack.html[`ThreadContextStack`],
then that column will be populated with the MDC or NDC respectively
(this is database-specific how they handle inserting a `Map` or `List`
value). If the configured type is assignment-compatible with
`java.util.Date`, then the log timestamp will be converted to that
configured date type. If the configured type is assignment-compatible
with `java.sql.Clob` or `java.sql.NClob`, then the formatted event will
be set as a Clob or NClob respectively (similar to the traditional
ColumnConfig plugin). If a `literal` attribute is given, then its value
will be used as is in the `INSERT` query without any escaping.
Otherwise, the layout or pattern specified will be converted into the
configured type and stored in that column.

|immediateFail |boolean |false |When set to true, log events will not
wait to try to reconnect and will fail immediately if the JDBC resources
are not available. New in 2.11.2.

|reconnectIntervalMillis |long |5000 |If set to a value greater than 0,
after an error, the JDBCDatabaseManager will attempt to reconnect to the database
after waiting the specified number of milliseconds. If the reconnect
fails then an exception will be thrown (which can be caught by the
application if `ignoreExceptions` is set to `false`). New in 2.11.2.
|=======================================================================

When configuring the JDBCAppender, you must specify a `ConnectionSource`
implementation from which the Appender gets JDBC connections. You must
use exactly one of the following nested elements:

* link:#JDBCDataSource[`<DataSource>`]: Uses JNDI.
* link:#JDBCConnectionFactory[`<ConnectionFactory>`]: Points to a
class-method pair to provide JDBC connections.
* link:#JDBCDriverManager[`<DriverManager>`]: A quick and dirty way to
get off the ground, no connection pooling.
* link:#JDBCPoolingDriver[`<PoolingDriver>`]: Uses Apache Commons DBCP
to provide connection pooling.

[#JDBCDataSource]
.DataSource Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|jndiName |String |_Required._ The full, prefixed JNDI name that the
`javax.sql.DataSource` is bound to, such as
`java:/comp/env/jdbc/LoggingDatabase`. The `DataSource` must be backed
by a connection pool; otherwise, logging will be very slow.
|=======================================================================

[#JDBCConnectionFactory]
.ConnectionFactory Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|class |Class |_Required._ The fully qualified name of a class
containing a static factory method for obtaining JDBC connections.

|method |Method |_Required._ The name of a static factory method for
obtaining JDBC connections. This method must have no parameters and its
return type must be either `java.sql.Connection` or `DataSource`. If the
method returns `Connection`s, it must obtain them from a connection pool
(and they will be returned to the pool when Log4j is done with them);
otherwise, logging will be very slow. If the method returns a
`DataSource`, the `DataSource` will only be retrieved once, and it must
be backed by a connection pool for the same reasons.
|=======================================================================

[#JDBCDriverManager]
.DriverManager Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|connectionString |String |_Required._ The driver-specific JDBC
connection string.

|userName |String |The database user name. You cannot specify both
properties and a user name or password.

|password |String |The database password. You cannot specify both
properties and a user name or password.

|driverClassName |String |The JDBC driver class name. Some old JDBC
Driver can only be discovered by explicitly loading them by class name.

|properties |Property[] |A list of properties. You cannot specify both
properties and a user name or password.
|=======================================================================

[#JDBCPoolingDriver]
.PoolingDriver Parameters (Apache Commons DBCP)
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|DriverManager parameters |DriverManager parameters |This connection
source inherits all parameter from the DriverManager connection source.

|poolName |String |The pool name used to pool JDBC Connections. Defaults
to `example`. You can use the JDBC connection string prefix
`jdbc:apache:commons:dbcp:` followed by the pool name if you want to use
a pooled connection elsewhere. For example:
`jdbc:apache:commons:dbcp:example`.

|PoolableConnectionFactory |PoolableConnectionFactory element |Defines a PoolableConnectionFactory.
|=======================================================================

[#JDBCPoolableConnectionFactory]
.PoolableConnectionFactory Parameters (Apache Commons DBCP)
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|autoCommitOnReturn |boolean | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|cacheState |boolean | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|connectionInitSqls |Strings | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|defaultAutoCommit |Boolean | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|defaultCatalog |String | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|defaultQueryTimeoutSeconds |Integer | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|defaultReadOnly |Boolean | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|defaultTransactionIsolation |int | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|disconnectionSqlCodes |Strings | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|fastFailValidation |boolean | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|maxConnLifetimeMillis |long | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|maxOpenPreparedStatements |int | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|poolStatements |boolean | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|rollbackOnReturn |boolean | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|validationQuery |String | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|validationQueryTimeoutSeconds |int | See http://commons.apache.org/proper/commons-dbcp/api-2.5.0/org/apache/commons/dbcp2/PoolableConnectionFactory.html[Apache Commons DBCP PoolableConnectionFactory.]
|=======================================================================

When configuring the JDBCAppender, use the nested `<Column>` elements to
specify which columns in the table should be written to and how to write
to them. The JDBCAppender uses this information to formulate a
`PreparedStatement` to insert records without SQL injection
vulnerability.

.Column Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |_Required._ The name of the database column.

|pattern |String |Use this attribute to insert a value or values from
the log event in this column using a `PatternLayout` pattern. Simply
specify any legal pattern in this attribute. Either this attribute,
`literal`, or `isEventTimestamp="true"` must be specified, but not more
than one of these.

|literal |String |Use this attribute to insert a literal value in this
column. The value will be included directly in the insert SQL, without
any quoting (which means that if you want this to be a string, your
value should contain single quotes around it like this:
`literal="'Literal String'"`). This is especially useful for databases
that don't support identity columns. For example, if you are using
Oracle you could specify `literal="NAME_OF_YOUR_SEQUENCE.NEXTVAL"` to
insert a unique ID in an ID column. Either this attribute, `pattern`, or
`isEventTimestamp="true"` must be specified, but not more than one of
these.

|parameter |String a|
Use this attribute to insert an expression with a parameter marker '?'
in this column. The value will be included directly in the insert SQL,
without any quoting (which means that if you want this to be a string,
your value should contain single quotes around it like this:

`<ColumnMapping name="instant" parameter="TIMESTAMPADD('MILLISECOND', ?, TIMESTAMP '1970-01-01')"/>`

You can only specify one of `literal` or `parameter`.

|isEventTimestamp |boolean |Use this attribute to insert the event
timestamp in this column, which should be a SQL datetime. The value will
be inserted as a `java.sql.Types.TIMESTAMP`. Either this attribute
(equal to `true`), `pattern`, or `isEventTimestamp` must be specified,
but not more than one of these.

|isUnicode |boolean |This attribute is ignored unless `pattern` is
specified. If `true` or omitted (default), the value will be inserted as
unicode (`setNString` or `setNClob`). Otherwise, the value will be
inserted non-unicode (`setString` or `setClob`).

|isClob |boolean |This attribute is ignored unless `pattern` is
specified. Use this attribute to indicate that the column stores
Character Large Objects (CLOBs). If `true`, the value will be inserted
as a CLOB (`setClob` or `setNClob`). If `false` or omitted (default),
the value will be inserted as a VARCHAR or NVARCHAR (`setString` or
`setNString`).
|=======================================================================

.ColumnMapping Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |_Required._ The name of the database column.

|pattern |String |Use this attribute to insert a value or values from
the log event in this column using a `PatternLayout` pattern. Simply
specify any legal pattern in this attribute. Either this attribute,
`literal`, or `isEventTimestamp="true"` must be specified, but not more
than one of these.

|literal |String |Use this attribute to insert a literal value in this
column. The value will be included directly in the insert SQL, without
any quoting (which means that if you want this to be a string, your
value should contain single quotes around it like this:
`literal="'Literal String'"`). This is especially useful for databases
that don't support identity columns. For example, if you are using
Oracle you could specify `literal="NAME_OF_YOUR_SEQUENCE.NEXTVAL"` to
insert a unique ID in an ID column. Either this attribute, `pattern`, or
`isEventTimestamp="true"` must be specified, but not more than one of
these.

|layout |Layout |The Layout to format the LogEvent.

|type |String |Conversion type name, a fully-qualified class name.
|=======================================================================

Here are a couple sample configurations for the JDBCAppender, as well as
a sample factory implementation that uses Commons Pooling and Commons
DBCP to pool database connections:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <JDBC name="databaseAppender" tableName="dbo.application_log">
      <DataSource jndiName="java:/comp/env/jdbc/LoggingDataSource" />
      <Column name="eventDate" isEventTimestamp="true" />
      <Column name="level" pattern="%level" />
      <Column name="logger" pattern="%logger" />
      <Column name="message" pattern="%message" />
      <Column name="exception" pattern="%ex{full}" />
    </JDBC>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
----

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <JDBC name="databaseAppender" tableName="LOGGING.APPLICATION_LOG">
      <ConnectionFactory class="net.example.db.ConnectionFactory" method="getDatabaseConnection" />
      <Column name="EVENT_ID" literal="LOGGING.APPLICATION_LOG_SEQUENCE.NEXTVAL" />
      <Column name="EVENT_DATE" isEventTimestamp="true" />
      <Column name="LEVEL" pattern="%level" />
      <Column name="LOGGER" pattern="%logger" />
      <Column name="MESSAGE" pattern="%message" />
      <Column name="THROWABLE" pattern="%ex{full}" />
    </JDBC>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
----

[source,java]
----
package net.example.db;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;

import javax.sql.DataSource;

import org.apache.commons.dbcp.DriverManagerConnectionFactory;
import org.apache.commons.dbcp.PoolableConnection;
import org.apache.commons.dbcp.PoolableConnectionFactory;
import org.apache.commons.dbcp.PoolingDataSource;
import org.apache.commons.pool.impl.GenericObjectPool;

public class ConnectionFactory {
    private static interface Singleton {
        final ConnectionFactory INSTANCE = new ConnectionFactory();
    }

    private final DataSource dataSource;

    private ConnectionFactory() {
        Properties properties = new Properties();
        properties.setProperty("user", "logging");
        properties.setProperty("password", "abc123"); // or get properties from some configuration file

        GenericObjectPool<PoolableConnection> pool = new GenericObjectPool<PoolableConnection>();
        DriverManagerConnectionFactory connectionFactory = new DriverManagerConnectionFactory(
                "jdbc:mysql://example.org:3306/exampleDb", properties
        );
        new PoolableConnectionFactory(
                connectionFactory, pool, null, "SELECT 1", 3, false, false, Connection.TRANSACTION_READ_COMMITTED
        );

        this.dataSource = new PoolingDataSource(pool);
    }

    public static Connection getDatabaseConnection() throws SQLException {
        return Singleton.INSTANCE.dataSource.getConnection();
    }
}
----

This appender is link:messages.html#MapMessage[`MapMessage`]-aware.

The following configuration uses a `MessageLayout` to indicate that the
Appender should match the keys of a `MapMessage` to the names of
`ColumnMapping`s when setting the values of the Appender's SQL INSERT
statement. This let you insert rows for custom values in a database
table based on a Log4j `MapMessage` instead of values from `LogEvent`s.

[source,xml]
----
<Configuration status="debug">

  <Appenders>
    <Console name="STDOUT">
      <PatternLayout pattern="%C{1.} %m %level MDC%X%n"/>
    </Console>
    <Jdbc name="databaseAppender" tableName="dsLogEntry" ignoreExceptions="false">
      <DataSource jndiName="java:/comp/env/jdbc/TestDataSourceAppender" />
      <ColumnMapping name="Id" />
      <ColumnMapping name="ColumnA" />
      <ColumnMapping name="ColumnB" />
      <MessageLayout />
    </Jdbc>
  </Appenders>

  <Loggers>
    <Logger name="org.apache.logging.log4j.core.appender.db" level="debug" additivity="false">
      <AppenderRef ref="databaseAppender" />
    </Logger>

    <Root level="fatal">
      <AppenderRef ref="STDOUT"/>
    </Root>
  </Loggers>

</Configuration>
----

[#JMSAppender]
== JMSAppender

[[JMSQueueAppender]] [[JMSTopicAppender]]
As of Log4j 2.11.0, JPA support has moved from the existing module
`log4j-core` to the new module `log4j-jms`.

The JMS Appender sends the formatted log event to a JMS Destination.

Note that in Log4j 2.0, this appender was split into a JMSQueueAppender
and a JMSTopicAppender. Starting in Log4j 2.1, these appenders were
combined into the JMS Appender which makes no distinction between queues
and topics. However, configurations written for 2.0 which use the
`<JMSQueue/>` or `<JMSTopic/>` elements will continue to work with the
new `<JMS/>` configuration element.

.JMS Appender Parameters
[cols=",,,",options="header",]
|=======================================================================
|Parameter Name |Type |Default |Description
|factoryBindingName |String |_Required_ |The name to locate in the
Context that provides the
https://download.oracle.com/javaee/5/api/javax/jms/ConnectionFactory.html[`ConnectionFactory`].
This can be any subinterface of `ConnectionFactory` as well.

|factoryName |String |_Required_ |The fully qualified class name that
should be used to define the Initial Context Factory as defined in
https://download.oracle.com/javase/7/docs/api/javax/naming/Context.html#INITIAL_CONTEXT_FACTORY[`INITIAL_CONTEXT_FACTORY`].
If a factoryName is specified without a providerURL a warning message
will be logged as this is likely to cause problems.

|filter |Filter |null |A Filter to determine if the event should be
handled by this Appender. More than one Filter may be used by using a
CompositeFilter.

|layout |Layout |_Required_ |The Layout to use to format the LogEvent.
_New since 2.9, in previous versions SerializedLayout was default._

|name |String |_Required_ |The name of the Appender.

|password |String |null |The password to use to create the JMS
connection.

|providerURL |String |_Required_ |The URL of the provider to use as
defined by
https://download.oracle.com/javase/7/docs/api/javax/naming/Context.html#PROVIDER_URL[`PROVIDER_URL`].

|destinationBindingName |String |_Required_ |The name to use to locate
the
https://download.oracle.com/javaee/5/api/javax/jms/Destination.html[`Destination`].
This can be a `Queue` or `Topic`, and as such, the attribute names
`queueBindingName` and `topicBindingName` are aliases to maintain
compatibility with the Log4j 2.0 JMS appenders.

|securityPrincipalName |String |null |The name of the identity of the
Principal as specified by
https://download.oracle.com/javase/7/docs/api/javax/naming/Context.html#SECURITY_PRINCIPAL[`SECURITY_PRINCIPAL`].
If a securityPrincipalName is specified without securityCredentials a
warning message will be logged as this is likely to cause problems.

|securityCredentials |String |null |The security credentials for the
principal as specified by
https://download.oracle.com/javase/7/docs/api/javax/naming/Context.html#SECURITY_CREDENTIALS[`SECURITY_CREDENTIALS`].

|ignoreExceptions |boolean |true |When `true`, exceptions caught while
appending events are internally logged and then ignored. When `false`
exceptions are propagated to the caller. You must set this to `false`
when wrapping this Appender in a
link:#FailoverAppender[FailoverAppender].

|immediateFail |boolean |false |When set to true, log events will not
wait to try to reconnect and will fail immediately if the JMS resources
are not available. New in 2.9.

|reconnectIntervalMillis |long |5000 |If set to a value greater than 0,
after an error, the JMSManager will attempt to reconnect to the broker
after waiting the specified number of milliseconds. If the reconnect
fails then an exception will be thrown (which can be caught by the
application if `ignoreExceptions` is set to `false`). New in 2.9.

|urlPkgPrefixes |String |null |A colon-separated list of package
prefixes for the class name of the factory class that will create a URL
context factory as defined by
https://download.oracle.com/javase/7/docs/api/javax/naming/Context.html#URL_PKG_PREFIXES[`URL_PKG_PREFIXES`].

|userName |String |null |The user id used to create the JMS connection.
|=======================================================================

Here is a sample JMS Appender configuration:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp">
  <Appenders>
    <JMS name="jmsQueue" destinationBindingName="MyQueue"
         factoryBindingName="MyQueueConnectionFactory">
      <JsonLayout properties="true"/>
    </JMS>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="jmsQueue"/>
    </Root>
  </Loggers>
</Configuration>
----

To map your Log4j `MapMessage`s to JMS `javax.jms.MapMessage`s, set the
layout of the appender to `MessageLayout` with `<MessageLayout />`
(Since 2.9.):

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp">
  <Appenders>
    <JMS name="jmsQueue" destinationBindingName="MyQueue"
         factoryBindingName="MyQueueConnectionFactory">
      <MessageLayout />
    </JMS>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="jmsQueue"/>
    </Root>
  </Loggers>
</Configuration>
----

[#JPAAppender]
== JPAAppender

As of Log4j 2.11.0, JPA support has moved from the existing module
`log4j-core` to the new module `log4j-jpa`.

The JPAAppender writes log events to a relational database table using
the Java Persistence API 2.1. It requires the API and a provider
implementation be on the classpath. It also requires a decorated entity
configured to persist to the table desired. The entity should either
extend
`org.apache.logging.log4j.core.appender.db.jpa.BasicLogEventEntity` (if
you mostly want to use the default mappings) and provide at least an
`@Id` property, or
`org.apache.logging.log4j.core.appender.db.jpa.AbstractLogEventWrapperEntity`
(if you want to significantly customize the mappings). See the Javadoc
for these two classes for more information. You can also consult the
source code of these two classes as an example of how to implement the
entity.

.JPAAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |_Required._ The name of the Appender.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|bufferSize |int |If an integer greater than 0, this causes the appender
to buffer log events and flush whenever the buffer reaches this size.

|entityClassName |String |_Required._ The fully qualified name of the
concrete LogEventWrapperEntity implementation that has JPA annotations
mapping it to a database table.

|persistenceUnitName |String |_Required._ The name of the JPA
persistence unit that should be used for persisting log events.
|=======================================================================

Here is a sample configuration for the JPAAppender. The first XML sample
is the Log4j configuration file, the second is the `persistence.xml`
file. EclipseLink is assumed here, but any JPA 2.1 or higher provider
will do. You should _always_ create a _separate_ persistence unit for
logging, for two reasons. First, `<shared-cache-mode>` _must_ be set to
"NONE," which is usually not desired in normal JPA usage. Also, for
performance reasons the logging entity should be isolated in its own
persistence unit away from all other entities and you should use a
non-JTA data source. Note that your persistence unit _must_ also contain
`<class>` elements for all of the
`org.apache.logging.log4j.core.appender.db.jpa.converter` converter
classes.

[source,prettyprint,linenums,lang-xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <JPA name="databaseAppender" persistenceUnitName="loggingPersistenceUnit"
         entityClassName="com.example.logging.JpaLogEntity" />
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
----

[source,prettyprint,linenums,lang-xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
                                 http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">

  <persistence-unit name="loggingPersistenceUnit" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextMapAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextMapJsonAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextStackAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ContextStackJsonAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.MarkerAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.MessageAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.StackTraceElementAttributeConverter</class>
    <class>org.apache.logging.log4j.core.appender.db.jpa.converter.ThrowableAttributeConverter</class>
    <class>com.example.logging.JpaLogEntity</class>
    <non-jta-data-source>jdbc/LoggingDataSource</non-jta-data-source>
    <shared-cache-mode>NONE</shared-cache-mode>
  </persistence-unit>

</persistence>
----

[source,prettyprint,linenums,lang-java]
----
package com.example.logging;
...
@Entity
@Table(name="application_log", schema="dbo")
public class JpaLogEntity extends BasicLogEventEntity {
    private static final long serialVersionUID = 1L;
    private long id = 0L;

    public TestEntity() {
        super(null);
    }
    public TestEntity(LogEvent wrappedEvent) {
        super(wrappedEvent);
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    public long getId() {
        return this.id;
    }

    public void setId(long id) {
        this.id = id;
    }

    // If you want to override the mapping of any properties mapped in BasicLogEventEntity,
    // just override the getters and re-specify the annotations.
}
----

[source,prettyprint,linenums,lang-java]
----
package com.example.logging;
...
@Entity
@Table(name="application_log", schema="dbo")
public class JpaLogEntity extends AbstractLogEventWrapperEntity {
    private static final long serialVersionUID = 1L;
    private long id = 0L;

    public TestEntity() {
        super(null);
    }
    public TestEntity(LogEvent wrappedEvent) {
        super(wrappedEvent);
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "logEventId")
    public long getId() {
        return this.id;
    }

    public void setId(long id) {
        this.id = id;
    }

    @Override
    @Enumerated(EnumType.STRING)
    @Column(name = "level")
    public Level getLevel() {
        return this.getWrappedEvent().getLevel();
    }

    @Override
    @Column(name = "logger")
    public String getLoggerName() {
        return this.getWrappedEvent().getLoggerName();
    }

    @Override
    @Column(name = "message")
    @Convert(converter = MyMessageConverter.class)
    public Message getMessage() {
        return this.getWrappedEvent().getMessage();
    }
    ...
}
----

[#HttpAppender]
== HttpAppender

The HttpAppender sends log events over HTTP. A Layout must be provided
to format the LogEvent.

Will set the `Content-Type` header according to the layout. Additional
headers can be specified with embedded Property elements.

Will wait for response from server, and throw error if no 2xx response
is received.

Implemented with
https://docs.oracle.com/javase/7/docs/api/java/net/HttpURLConnection.html[HttpURLConnection].

.HttpAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |The name of the Appender.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|layout |Layout |The Layout to use to format the LogEvent.

|Ssl |SslConfiguration |Contains the configuration for the KeyStore and
TrustStore for https. Optional, uses Java runtime defaults if not
specified. See link:#SSL[SSL]

|verifyHostname |boolean |Whether to verify server hostname against
certificate. Only valid for https. Optional, defaults to true

|url |string |The URL to use. The URL scheme must be "http" or "https".

|method |string |The HTTP method to use. Optional, default is "POST".

|connectTimeoutMillis |integer |The connect timeout in milliseconds.
Optional, default is 0 (infinite timeout).

|readTimeoutMillis |integer |The socket read timeout in milliseconds.
Optional, default is 0 (infinite timeout).

|headers |Property[] |Additional HTTP headers to use. The values support
link:lookups.html[lookups].

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].
|=======================================================================

Here is a sample HttpAppender configuration snippet:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
  ...
  <Appenders>
    <Http name="Http" url="https://localhost:9200/test/log4j/">
      <Property name="X-Java-Runtime" value="$${java:runtime}" />
      <JsonLayout properties="true"/>
      <SSL>
        <KeyStore   location="log4j2-keystore.jks" passwordEnvironmentVariable="KEYSTORE_PASSWORD"/>
        <TrustStore location="truststore.jks"      passwordFile="${sys:user.home}/truststore.pwd"/>
      </SSL>
    </Http>
  </Appenders>
----

[#KafkaAppender]
== KafkaAppender

As of Log4j 2.11.0, https://kafka.apache.org/[Apache Kafka] support has
moved from the existing module `log4j-core` to the new module
`log4j-kafka`.

The KafkaAppender logs events to an https://kafka.apache.org/[Apache
Kafka] topic. Each log event is sent as a Kafka record.

.KafkaAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|topic |String |The Kafka topic to use. Required.

|key |String |The key that will be sent to Kafka with every message.
Optional value defaulting to `null`. Any of the
link:./lookups.html[Lookups]) can be included.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|layout |Layout |The Layout to use to format the LogEvent. Required,
there is no default. _New since 2.9, in previous versions <PatternLayout
pattern="%m"/> was default._

|name |String |The name of the Appender. Required.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|syncSend |boolean |The default is `true`, causing sends to block until
the record has been acknowledged by the Kafka server. When set to
`false` sends return immediately, allowing for lower latency and
significantly higher throughput. _New since 2.8. Be aware that this is a
new addition, and it has not been extensively tested. Any failure
sending to Kafka will be reported as error to StatusLogger and the log
event will be dropped (the ignoreExceptions parameter will not be
effective). Log events may arrive out of order to the Kafka server._

|properties |Property[] |You can set properties in
http://kafka.apache.org/documentation.html#producerconfigs[Kafka
producer properties]. You need to set the `bootstrap.servers` property,
there are sensible default values for the others. Do not set the
`value.serializer` nor `key.serializer` properties.
|=======================================================================

Here is a sample KafkaAppender configuration snippet:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
  ...
  <Appenders>
    <Kafka name="Kafka" topic="log-test">
      <PatternLayout pattern="%date %message"/>
        <Property name="bootstrap.servers">localhost:9092</Property>
    </Kafka>
  </Appenders>
----

This appender is synchronous by default and will block until the record
has been acknowledged by the Kafka server, timeout for this can be set
with the `timeout.ms` property (defaults to 30 seconds). Wrap with
http://logging.apache.org/log4j/2.x/manual/appenders.html#AsyncAppender[Async
appender] and/or set syncSend to `false` to log asynchronously.

This appender requires the http://kafka.apache.org/[Kafka client
library]. Note that you need to use a version of the Kafka client
library matching the Kafka server used.

__Note:__Make sure to not let `org.apache.kafka` log to a Kafka appender
on DEBUG level, since that will cause recursive logging:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
  ...
  <Loggers>
    <Root level="DEBUG">
      <AppenderRef ref="Kafka"/>
    </Root>
    <Logger name="org.apache.kafka" level="INFO" /> <!-- avoid recursive logging -->
  </Loggers>
----

[#MemoryMappedFileAppender]
== MemoryMappedFileAppender

_New since 2.1. Be aware that this is a new addition, and although it
has been tested on several platforms, it does not have as much track
record as the other file appenders._

The MemoryMappedFileAppender maps a part of the specified file into
memory and writes log events to this memory, relying on the operating
system's virtual memory manager to synchronize the changes to the
storage device. The main benefit of using memory mapped files is I/O
performance. Instead of making system calls to write to disk, this
appender can simply change the program's local memory, which is orders
of magnitude faster. Also, in most operating systems the memory region
mapped actually is the kernel's
http://en.wikipedia.org/wiki/Page_cache[page cache] (file cache),
meaning that no copies need to be created in user space. (TODO:
performance tests that compare performance of this appender to
RandomAccessFileAppender and FileAppender.)

There is some overhead with mapping a file region into memory,
especially very large regions (half a gigabyte or more). The default
region size is 32 MB, which should strike a reasonable balance between
the frequency and the duration of remap operations. (TODO: performance
test remapping various sizes.)

Similar to the FileAppender and the RandomAccessFileAppender,
MemoryMappedFileAppender uses a MemoryMappedFileManager to actually
perform the file I/O. While MemoryMappedFileAppender from different
Configurations cannot be shared, the MemoryMappedFileManagers can be if
the Manager is accessible. For example, two web applications in a
servlet container can have their own configuration and safely write to
the same file if Log4j is in a ClassLoader that is common to both of
them.

.MemoryMappedFileAppender Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|append |boolean |When true - the default, records will be appended to
the end of the file. When set to false, the file will be cleared before
new records are written.

|fileName |String |The name of the file to write to. If the file, or any
of its parent directories, do not exist, they will be created.

|filters |Filter |A Filter to determine if the event should be handled
by this Appender. More than one Filter may be used by using a
CompositeFilter.

|immediateFlush |boolean a|
When set to true, each write will be followed by a call to
http://docs.oracle.com/javase/7/docs/api/java/nio/MappedByteBuffer.html#force()[MappedByteBuffer.force()].
This will guarantee the data is written to the storage device.

The default for this parameter is `false`. This means that the data is
written to the storage device even if the Java process crashes, but
there may be data loss if the operating system crashes.

Note that manually forcing a sync on every log event loses most of the
performance benefits of using a memory mapped file.

Flushing after every write is only useful when using this appender with
synchronous loggers. Asynchronous loggers and appenders will
automatically flush at the end of a batch of events, even if
immediateFlush is set to false. This also guarantees the data is written
to disk but is more efficient.

|regionLength |int |The length of the mapped region, defaults to 32 MB
(32 * 1024 * 1024 bytes). This parameter must be a value between 256 and
1,073,741,824 (1 GB or 2^30); values outside this range will be adjusted
to the closest valid value. Log4j will round the specified value up to
the nearest power of two.

|layout |Layout |The Layout to use to format the LogEvent. If no layout
is supplied the default pattern layout of "%m%n" will be used.

|name |String |The name of the Appender.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].
|=======================================================================

Here is a sample MemoryMappedFile configuration:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <MemoryMappedFile name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </MemoryMappedFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="MyFile"/>
    </Root>
  </Loggers>
</Configuration>
----

[#NoSQLAppender]
== NoSQLAppender

The NoSQLAppender writes log events to a NoSQL database using an
internal lightweight provider interface. Provider implementations
currently exist for MongoDB and Apache CouchDB, and writing a custom
provider is quite simple.

.NoSQLAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |_Required._ The name of the Appender.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|bufferSize |int |If an integer greater than 0, this causes the appender
to buffer log events and flush whenever the buffer reaches this size.

|NoSqlProvider |NoSQLProvider<C extends NoSQLConnection<W, T extends
NoSQLObject<W>>> |_Required._ The NoSQL provider that provides
connections to the chosen NoSQL database.
|=======================================================================

You specify which NoSQL provider to use by specifying the appropriate
configuration element within the `<NoSql>` element. The types currently
supported are `<MongoDb>` and `<CouchDb>`. To create your own custom
provider, read the JavaDoc for the `NoSQLProvider`, `NoSQLConnection`,
and `NoSQLObject` classes and the documentation about creating Log4j
plugins. We recommend you review the source code for the MongoDB and
CouchDB providers as a guide for creating your own provider.

The following example demonstrates how log events are persisted in NoSQL
databases if represented in a JSON format:

[source,prettyprint,lang-javascript]
----
{
    "level": "WARN",
    "loggerName": "com.example.application.MyClass",
    "message": "Something happened that you might want to know about.",
    "source": {
        "className": "com.example.application.MyClass",
        "methodName": "exampleMethod",
        "fileName": "MyClass.java",
        "lineNumber": 81
    },
    "marker": {
        "name": "SomeMarker",
        "parent" {
            "name": "SomeParentMarker"
        }
    },
    "threadName": "Thread-1",
    "millis": 1368844166761,
    "date": "2013-05-18T02:29:26.761Z",
    "thrown": {
        "type": "java.sql.SQLException",
        "message": "Could not insert record. Connection lost.",
        "stackTrace": [
                { "className": "org.example.sql.driver.PreparedStatement$1", "methodName": "responder", "fileName": "PreparedStatement.java", "lineNumber": 1049 },
                { "className": "org.example.sql.driver.PreparedStatement", "methodName": "executeUpdate", "fileName": "PreparedStatement.java", "lineNumber": 738 },
                { "className": "com.example.application.MyClass", "methodName": "exampleMethod", "fileName": "MyClass.java", "lineNumber": 81 },
                { "className": "com.example.application.MainClass", "methodName": "main", "fileName": "MainClass.java", "lineNumber": 52 }
        ],
        "cause": {
            "type": "java.io.IOException",
            "message": "Connection lost.",
            "stackTrace": [
                { "className": "java.nio.channels.SocketChannel", "methodName": "write", "fileName": null, "lineNumber": -1 },
                { "className": "org.example.sql.driver.PreparedStatement$1", "methodName": "responder", "fileName": "PreparedStatement.java", "lineNumber": 1032 },
                { "className": "org.example.sql.driver.PreparedStatement", "methodName": "executeUpdate", "fileName": "PreparedStatement.java", "lineNumber": 738 },
                { "className": "com.example.application.MyClass", "methodName": "exampleMethod", "fileName": "MyClass.java", "lineNumber": 81 },
                { "className": "com.example.application.MainClass", "methodName": "main", "fileName": "MainClass.java", "lineNumber": 52 }
            ]
        }
    },
    "contextMap": {
        "ID": "86c3a497-4e67-4eed-9d6a-2e5797324d7b",
        "username": "JohnDoe"
    },
    "contextStack": [
        "topItem",
        "anotherItem",
        "bottomItem"
    ]
}
----

[#NoSQLAppenderMongoDB]
== NoSQLAppenderMongoDB

We provide the following MongoDB modules:

* Added in 2.11.0: `log4j-mongodb3` defines the configuration element
link:#NoSQLAppenderMongoDB3[`MongoDb3`] matching the MongoDB Driver
version 3.
* Added in 2.14.0: `log4j-mongodb4` defines the configuration element
link:#NoSQLAppenderMongoDB4[`MongoDb4`] matching the MongoDB Driver
version 4.

We no longer provide the modules `log4j-mongodb` and `log4j-mongodb2`.

[#NoSQLAppenderMongoDB3]
== NoSQLAppenderMongoDB3

This section details specializations of the
link:#NoSQLAppender[NoSQLAppender] provider for MongoDB using the
MongoDB driver version 3. The NoSQLAppender Appender writes log events
to a NoSQL database using an internal lightweight provider interface.

.MongoDB3 Provider Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|collectionName |String |_Required._ The name of the MongoDB collection
to insert the events into.

|writeConcernConstant |Field |By default, the MongoDB provider inserts
records with the instructions `com.mongodb.WriteConcern.ACKNOWLEDGED`.
Use this optional attribute to specify the name of a constant other than
`ACKNOWLEDGED`.

|writeConcernConstantClass |Class |If you specify
`writeConcernConstant`, you can use this attribute to specify a class
other than `com.mongodb.WriteConcern` to find the constant on (to create
your own custom instructions).

|factoryClassName |Class |To provide a connection to the MongoDB
database, you can use this attribute and `factoryMethodName` to specify
a class and static method to get the connection from. The method must
return a `com.mongodb.client.MongoDatabase` or a
`com.mongodb.MongoClient`. If the `com.mongodb.client.MongoDatabase` is
not authenticated, you must also specify a `username` and `password`. If
you use the factory method for providing a connection, you must not
specify the `databaseName`, `server`, or `port` attributes.

|factoryMethodName |Method |See the documentation for attribute
`factoryClassName`.

|databaseName |String |If you do not specify a `factoryClassName` and
`factoryMethodName` for providing a MongoDB connection, you must specify
a MongoDB database name using this attribute. You must also specify a
`username` and `password`. You can optionally also specify a `server`
(defaults to localhost), and a `port` (defaults to the default MongoDB
port).

|server |String |See the documentation for attribute `databaseName`.

|port |int |See the documentation for attribute `databaseName`.

|username |String |See the documentation for attributes `databaseName`
and `factoryClassName`.

|password |String |See the documentation for attributes `databaseName`
and `factoryClassName`.

|capped |boolean |Enable support for
https://docs.mongodb.com/manual/core/capped-collections/[capped
collections]

|collectionSize |int |Specify the size in bytes of the capped collection
to use if enabled. The minimum size is 4096 bytes, and larger sizes will
be increased to the nearest integer multiple of 256. See the capped
collection documentation linked above for more information.
|=======================================================================

This appender is link:messages.html#MapMessage[MapMessage]-aware.

Here are a few sample configurations for the NoSQLAppender and MongoDB3
provider:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <NoSql name="databaseAppender">
      <MongoDb3 databaseName="applicationDb" collectionName="applicationLog" server="mongo.example.org"
               username="loggingUser" password="abc123" />
    </NoSql>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
----

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <NoSql name="databaseAppender">
      <MongoDb3 collectionName="applicationLog" factoryClassName="org.example.db.ConnectionFactory"
               factoryMethodName="getNewMongoClient" />
    </NoSql>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
----

[#NoSQLAppenderMongoDB4]
== NoSQLAppenderMongoDB4

This section details specializations of the
link:#NoSQLAppender[NoSQLAppender] provider for MongoDB using the
MongoDB driver version 4. The NoSQLAppender Appender writes log events
to a NoSQL database using an internal lightweight provider interface.

.MongoDB3 Provider Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|connection |String |_Required._ The MongoDB 
http://mongodb.github.io/mongo-java-driver/4.0/apidocs/mongodb-driver-core/com/mongodb/ConnectionString.html?is-external=true"[connection string] 
in the format `mongodb://[username:password@]host1[:port1][,host2[:port2],...[,hostN[:portN]]][/[database.collection][?options]]`.

|capped |boolean |Enable support for
https://docs.mongodb.com/manual/core/capped-collections/[capped
collections]

|collectionSize |int |Specify the size in bytes of the capped collection
to use if enabled. The minimum size is 4096 bytes, and larger sizes will
be increased to the nearest integer multiple of 256. See the capped
collection documentation linked above for more information.
|=======================================================================

This appender is link:messages.html#MapMessage[MapMessage]-aware.

Here are a few sample configurations for the NoSQLAppender and MongoDB4
provider:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
  <Appenders>
    <NoSql name="MongoDbAppender">
      <MongoDb4 connection="mongodb://log4jUser:12345678@localhost:${sys:MongoDBTestPort:-27017}/testDb.testCollection" />
    </NoSql>
  </Appenders>
  <Loggers>
    <Root level="ALL">
      <AppenderRef ref="MongoDbAppender" />
    </Root>
  </Loggers>
</Configuration>
----

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
  <Appenders>
    <NoSql name="MongoDbAppender">
      <MongoDb4 
        connection="mongodb://localhost:${sys:MongoDBTestPort:-27017}/testDb.testCollection" 
        capped="true" 
        collectionSize="1073741824"/>
    </NoSql>
  </Appenders>
  <Loggers>
    <Root level="ALL">
      <AppenderRef ref="MongoDbAppender" />
    </Root>
  </Loggers>
</Configuration>
----

[#NoSQLAppenderCouchDB]
== NoSQLAppenderCouchDB

This section details specializations of the
link:#NoSQLAppender[NoSQLAppender] provider for CouchDB. The
NoSQLAppender writes log events to a NoSQL database using an internal
lightweight provider interface.

.CouchDB Provider Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|factoryClassName |Class |To provide a connection to the CouchDB
database, you can use this attribute and `factoryMethodName` to specify
a class and static method to get the connection from. The method must
return a `org.lightcouch.CouchDbClient` or a
`org.lightcouch.CouchDbProperties`. If you use the factory method for
providing a connection, you must not specify the `databaseName`,
`protocol`, `server`, `port`, `username`, or `password` attributes.

|factoryMethodName |Method |See the documentation for attribute
`factoryClassName`.

|databaseName |String |If you do not specify a `factoryClassName` and
`factoryMethodName` for providing a CouchDB connection, you must specify
a CouchDB database name using this attribute. You must also specify a
`username` and `password`. You can optionally also specify a `protocol`
(defaults to http), `server` (defaults to localhost), and a `port`
(defaults to 80 for http and 443 for https).

|protocol |String |Must either be "http" or "https." See the
documentation for attribute `databaseName`.

|server |String |See the documentation for attribute `databaseName`.

|port |int |See the documentation for attribute `databaseName`.

|username |String |See the documentation for attributes `databaseName`.

|password |String |See the documentation for attributes `databaseName`.
|=======================================================================

Here are a few sample configurations for the NoSQLAppender and CouchDB
provider:

[source,prettyprint,linenums,lang-xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="error">
  <Appenders>
    <NoSql name="databaseAppender">
      <CouchDb databaseName="applicationDb" protocol="https" server="couch.example.org"
               username="loggingUser" password="abc123" />
    </NoSql>
  </Appenders>
  <Loggers>
    <Root level="warn">
      <AppenderRef ref="databaseAppender"/>
    </Root>
  </Loggers>
</Configuration>
----

[#OutputStreamAppender]
== OutputStreamAppender

The OutputStreamAppender provides the base for many of the other
Appenders such as the File and Socket appenders that write the event to
an Output Stream. It cannot be directly configured. Support for
immediateFlush and buffering is provided by the OutputStreamAppender.
The OutputStreamAppender uses an OutputStreamManager to handle the
actual I/O, allowing the stream to be shared by Appenders in multiple
configurations.

[#RandomAccessFileAppender]
== RandomAccessFileAppender

The RandomAccessFileAppender is similar to the standard
link:#FileAppender[FileAppender] except it is always buffered (this
cannot be switched off) and internally it uses a
`ByteBuffer + RandomAccessFile` instead of a `BufferedOutputStream`. We
saw a 20-200% performance improvement compared to FileAppender with
"bufferedIO=true" in our
link:../performance.html#whichAppender[measurements]. Similar to the
FileAppender, RandomAccessFileAppender uses a RandomAccessFileManager to
actually perform the file I/O. While RandomAccessFileAppender from
different Configurations cannot be shared, the RandomAccessFileManagers
can be if the Manager is accessible. For example, two web applications
in a servlet container can have their own configuration and safely write
to the same file if Log4j is in a ClassLoader that is common to both of
them.

.RandomAccessFileAppender Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|append |boolean |When true - the default, records will be appended to
the end of the file. When set to false, the file will be cleared before
new records are written.

|fileName |String |The name of the file to write to. If the file, or any
of its parent directories, do not exist, they will be created.

|filters |Filter |A Filter to determine if the event should be handled
by this Appender. More than one Filter may be used by using a
CompositeFilter.

|immediateFlush |boolean a|
When set to true - the default, each write will be followed by a flush.
This will guarantee that the data is passed to the operating system for writing;
it does not guarantee that the data is actually written to a physical device
such as a disk drive.

Note that if this flag is set to false, and the logging activity is sparse,
there may be an indefinite delay in the data eventually making it to the
operating system, because it is held up in a buffer.
This can cause surprising effects such as the logs not
appearing in the tail output of a file immediately after writing to the log.

Flushing after every write is only useful when using this appender with
synchronous loggers. Asynchronous loggers and appenders will
automatically flush at the end of a batch of events, even if
immediateFlush is set to false. This also guarantees the data is passed
to the operating system but is more efficient.

|bufferSize |int |The buffer size, defaults to 262,144 bytes (256 *
1024).

|layout |Layout |The Layout to use to format the LogEvent. If no layout
is supplied the default pattern layout of "%m%n" will be used.

|name |String |The name of the Appender.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].
|=======================================================================

Here is a sample RandomAccessFile configuration:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RandomAccessFile name="MyFile" fileName="logs/app.log">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
    </RandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="MyFile"/>
    </Root>
  </Loggers>
</Configuration>
----


[#RedisAppender]
== RedisAppender

Log4j2 supports a RedisAppender as part of the `log4j2-redis` module. The RedisAppender logs events to a https://redis.io/[Redis] queue. Each log event is appended via the standard
https://redis.io/commands/rpush[RPUSH] command.

.RedisAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description

|name |String |The name of the Appender. Required.

|layout |Layout |The Layout to use to format the LogEvent. Required,
there is no default. _New since 2.9, in previous versions <PatternLayout
pattern="%m"/> was default._

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|host |String |The hostname on which Redis is running (required).

|port |int |The port on which Redis is running. Default: 6379.

|keys |String |The keys of the queue to which each log message should be sent, separated by commas (e.g. "key-one,key-two,key-three"). Default: "logEvents".

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|immediateFlush | boolean | Whether to immediately send logs to redis rather than sending at the end of a batch. Default: true.

|queueCapacity | int | The maximum number of logs to hold in memory before sending to Redis. Default: 20.

|SslConfiguration |SslConfiguration |Contains the configuration for the KeyStore and
TrustStore. See link:#SSL[SSL].

|RedisPoolConfiguration |LoggingRedisPoolConfiguration |Granular configuration of the resource pool for the Redis
client connection. Available parameters include maxIdle, minIdle, testOnBorrow, testOnReturn, testWhileIdle, numTestsPerEvictionRun, and timeBetweenEvictionRunsMillis.
|=======================================================================

Here is a sample RedisAppender configuration snippet in XML:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
  ...
  <Appenders>
    <Redis name"RedisAppend" host="localhost" port=6379 keys="key-one,key-two" immediateFlush=false>
      <PatternLayout>
        <Pattern>%m</Pattern>
      </PatternLayout>
    </Redis>
    <Async name="Async">
      <AppenderRef ref="RedisAppend"/>
    </Async>
  </Appenders>
----
You can also configure the appender easily in YML:
[source,prettyprint,linenums]
----
Configuration:
  Appenders:
    Redis:
      name: RedisAppend
      host: localhost
      port: 6379
      Keys: key-one,key-two
      PatternLayout:
        pattern: "%m"
----


This appender operates synchronously by default and will block until the record
has been acknowledged by the Redis server. Wrap with
http://logging.apache.org/log4j/2.x/manual/appenders.html#AsyncAppender[Async
appender] and/or set syncSend to `false` to log asynchronously (as in the first example above).

=== Redis vs. Kafka

In a logging context, Redis may play a similar role to Kafka, serving as a message broker
in logging pipelines. In general, Redis may be preferred to Kafka in situations where
an in-memory queue is desired. A fairly simple breakdown of the diffferent approaches can be found
https://stackoverflow.com/questions/37990784/difference-between-redis-and-kafka[on StackOverflow here].

If you prefer to use Kafka, please refer to the supported <<KafkaAppender>>.

[#RewriteAppender]
== RewriteAppender

The RewriteAppender allows the LogEvent to manipulated before it is
processed by another Appender. This can be used to mask sensitive
information such as passwords or to inject information into each event.
The RewriteAppender must be configured with a RewritePolicy. The
RewriteAppender should be configured after any Appenders it references
to allow it to shut down properly.

.RewriteAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|AppenderRef |String |The name of the Appenders to call after the
LogEvent has been manipulated. Multiple AppenderRef elements can be
configured.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|name |String |The name of the Appender.

|rewritePolicy |RewritePolicy |The RewritePolicy that will manipulate
the LogEvent.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].
|=======================================================================

[#RewritePolicy]
===== RewritePolicy

RewritePolicy is an interface that allows implementations to inspect and
possibly modify LogEvents before they are passed to Appender.
RewritePolicy declares a single method named rewrite that must be
implemented. The method is passed the LogEvent and can return the same
event or create a new one.

MapRewritePolicy

MapRewritePolicy will evaluate LogEvents that contain a MapMessage and
will add or update elements of the Map.

[cols=",,",options="header",]
|================================================================
|Parameter Name |Type |Description
|mode |String |"Add" or "Update"
|keyValuePair |KeyValuePair[] |An array of keys and their values.
|================================================================

The following configuration shows a RewriteAppender configured to add a
product key and its value to the MapMessage.:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Rewrite name="rewrite">
      <AppenderRef ref="STDOUT"/>
      <MapRewritePolicy mode="Add">
        <KeyValuePair key="product" value="TestProduct"/>
      </MapRewritePolicy>
    </Rewrite>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Rewrite"/>
    </Root>
  </Loggers>
</Configuration>
----

PropertiesRewritePolicy

PropertiesRewritePolicy will add properties configured on the policy to
the ThreadContext Map being logged. The properties will not be added to
the actual ThreadContext Map. The property values may contain variables
that will be evaluated when the configuration is processed as well as
when the event is logged.

[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|properties |Property[] |One of more Property elements to define the
keys and values to be added to the ThreadContext Map.
|=======================================================================

The following configuration shows a RewriteAppender configured to add a
product key and its value to the MapMessage:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Rewrite name="rewrite">
      <AppenderRef ref="STDOUT"/>
      <PropertiesRewritePolicy>
        <Property name="user">${sys:user.name}</Property>
        <Property name="env">${sys:environment}</Property>
      </PropertiesRewritePolicy>
    </Rewrite>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Rewrite"/>
    </Root>
  </Loggers>
</Configuration>
----

LoggerNameLevelRewritePolicy

You can use this policy to make loggers in third party code less chatty
by changing event levels. The LoggerNameLevelRewritePolicy will rewrite
log event levels for a given logger name prefix. You configure a
LoggerNameLevelRewritePolicy with a logger name prefix and a pairs of
levels, where a pair defines a source level and a target level.

[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|logger |String |A logger name used as a prefix to test each event's
logger name.

|LevelPair |KeyValuePair[] |An array of keys and their values, each key
is a source level, each value a target level.
|=======================================================================

The following configuration shows a RewriteAppender configured to map
level INFO to DEBUG and level WARN to INFO for all loggers that start
with `com.foo.bar`.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT">
      <PatternLayout pattern="%m%n"/>
    </Console>
    <Rewrite name="rewrite">
      <AppenderRef ref="STDOUT"/>
      <LoggerNameLevelRewritePolicy logger="com.foo.bar">
        <KeyValuePair key="INFO" value="DEBUG"/>
        <KeyValuePair key="WARN" value="INFO"/>
      </LoggerNameLevelRewritePolicy>
    </Rewrite>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Rewrite"/>
    </Root>
  </Loggers>
</Configuration>
----

[#RollingFileAppender]
== RollingFileAppender

The RollingFileAppender is an OutputStreamAppender that writes to the
File named in the fileName parameter and rolls the file over according
the TriggeringPolicy and the RolloverPolicy. The RollingFileAppender
uses a RollingFileManager (which extends OutputStreamManager) to
actually perform the file I/O and perform the rollover. While
RolloverFileAppenders from different Configurations cannot be shared,
the RollingFileManagers can be if the Manager is accessible. For
example, two web applications in a servlet container can have their own
configuration and safely write to the same file if Log4j is in a
ClassLoader that is common to both of them.

A RollingFileAppender requires a
link:#TriggeringPolicies[TriggeringPolicy] and a
link:#RolloverStrategies[RolloverStrategy]. The triggering policy
determines if a rollover should be performed while the RolloverStrategy
defines how the rollover should be done. If no RolloverStrategy is
configured, RollingFileAppender will use the
link:#DefaultRolloverStrategy[DefaultRolloverStrategy]. Since log4j-2.5,
a link:#CustomDeleteOnRollover[custom delete action] can be configured
in the DefaultRolloverStrategy to run at rollover. Since 2.8 if no file
name is configured then
link:#DirectWriteRolloverStrategy[DirectWriteRolloverStrategy] will be
used instead of DefaultRolloverStrategy. Since log4j-2.9, a
link:#CustomPosixViewAttributeOnRollover[custom POSIX file attribute
view action] can be configured in the DefaultRolloverStrategy to run at
rollover, if not defined, inherited POSIX file attribute view from the
RollingFileAppender will be applied.

File locking is not supported by the RollingFileAppender.

.RollingFileAppender Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|append |boolean |When true - the default, records will be appended to
the end of the file. When set to false, the file will be cleared before
new records are written.

|bufferedIO |boolean |When true - the default, records will be written
to a buffer and the data will be written to disk when the buffer is full
or, if immediateFlush is set, when the record is written. File locking
cannot be used with bufferedIO. Performance tests have shown that using
buffered I/O significantly improves performance, even if immediateFlush
is enabled.

|bufferSize |int |When bufferedIO is true, this is the buffer size, the
default is 8192 bytes.

|createOnDemand |boolean |The appender creates the file on-demand. The
appender only creates the file when a log event passes all filters and
is routed to this appender. Defaults to false.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|fileName |String |The name of the file to write to. If the file, or any
of its parent directories, do not exist, they will be created.

|filePattern |String |The pattern of the file name of the archived log
file. The format of the pattern is dependent on the RolloverPolicy that
is used. The DefaultRolloverPolicy will accept both a date/time pattern
compatible with
https://download.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html[`SimpleDateFormat`]
and/or a %i which represents an integer counter. The integer counter
allows specifying a padding, like %3i for space-padding the counter to
3 digits or (usually more useful) %03i for zero-padding the counter to
3 digits. The pattern also
supports interpolation at runtime so any of the Lookups (such as the
link:./lookups.html#DateLookup[DateLookup]) can be included in the
pattern.

|immediateFlush |boolean a|
When set to true - the default, each write will be followed by a flush.
This will guarantee that the data is passed to the operating system for writing;
it does not guarantee that the data is actually written to a physical device
such as a disk drive.

Note that if this flag is set to false, and the logging activity is sparse,
there may be an indefinite delay in the data eventually making it to the
operating system, because it is held up in a buffer.
This can cause surprising effects such as the logs not
appearing in the tail output of a file immediately after writing to the log.

Flushing after every write is only useful when using this appender with
synchronous loggers. Asynchronous loggers and appenders will
automatically flush at the end of a batch of events, even if
immediateFlush is set to false. This also guarantees the data is passed
to the operating system but is more efficient.

|layout |Layout |The Layout to use to format the LogEvent. If no layout
is supplied the default pattern layout of "%m%n" will be used.

|name |String |The name of the Appender.

|policy |TriggeringPolicy |The policy to use to determine if a rollover
should occur.

|strategy |RolloverStrategy |The strategy to use to determine the name
and location of the archive file.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|filePermissions |String a|
File attribute permissions in POSIX format to apply whenever the file is
created.

Underlying files system shall support
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/PosixFileAttributeView.html[POSIX]
file attribute view.

Examples: rw------- or rw-rw-rw- etc...

|fileOwner |String a|
File owner to define whenever the file is created.

Changing file's owner may be restricted for security reason and
Operation not permitted IOException thrown. Only processes with an
effective user ID equal to the user ID of the file or with appropriate
privileges may change the ownership of a file if
http://www.gnu.org/software/libc/manual/html_node/Options-for-Files.html[_POSIX_CHOWN_RESTRICTED]
is in effect for path.

Underlying files system shall support file
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/FileOwnerAttributeView.html[owner]
attribute view.

|fileGroup |String a|
File group to define whenever the file is created.

Underlying files system shall support
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/PosixFileAttributeView.html[POSIX]
file attribute view.

|=======================================================================

[#TriggeringPolicies]
== TriggeringPolicies

[#Triggering]
===== Triggering Policies

Composite Triggering Policy

The `CompositeTriggeringPolicy` combines multiple triggering policies
and returns true if any of the configured policies return true. The
`CompositeTriggeringPolicy` is configured simply by wrapping other
policies in a `Policies` element.

For example, the following XML fragment defines policies that rollover
the log when the JVM starts, when the log size reaches twenty megabytes,
and when the current date no longer matches the log’s start date.

[source,prettyprint,linenums]
----
<Policies>
  <OnStartupTriggeringPolicy />
  <SizeBasedTriggeringPolicy size="20 MB" />
  <TimeBasedTriggeringPolicy />
</Policies>
----

Cron Triggering Policy

The `CronTriggeringPolicy` triggers rollover based on a cron expression. This policy
is controlled by a timer and is asynchronous to processing log events, so it is possible that log events
from the previous or next time period may appear at the beginning or end of the log file.
The filePattern attribute of the Appender should contain a timestamp otherwise the target file will be
overwritten on each rollover.

.CronTriggeringPolicy Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|schedule |String |The cron expression. The expression is the same as
what is allowed in the Quartz scheduler. See
link:../log4j-core/apidocs/org/apache/logging/log4j/core/util/CronExpression.html[CronExpression]
for a full description of the expression.

|evaluateOnStartup |boolean |On startup the cron expression will be
evaluated against the file's last modification timestamp. If the cron
expression indicates a rollover should have occurred between that time
and the current time the file will be immediately rolled over.
|=======================================================================

OnStartup Triggering Policy

The `OnStartupTriggeringPolicy` policy causes a rollover if the log file
is older than the current JVM's start time and the minimum file size is
met or exceeded.

.OnStartupTriggeringPolicy Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|minSize |long |The minimum size the file must have to roll over. A size
of zero will cause a roll over no matter what the file size is. The
default value is 1, which will prevent rolling over an empty file.
|=======================================================================

_Google App Engine note:_ +
When running in Google App Engine, the OnStartup policy causes a
rollover if the log file is older than _the time when Log4J
initialized_. (Google App Engine restricts access to certain classes so
Log4J cannot determine JVM start time with
`java.lang.management.ManagementFactory.getRuntimeMXBean().getStartTime()`
and falls back to Log4J initialization time instead.)

SizeBased Triggering Policy

The `SizeBasedTriggeringPolicy` causes a rollover once the file has reached the specified size. The size can be
specified in bytes, with the suffix KB, MB or GB, for example `20MB`.
When combined with a time based triggering policy the file pattern must contain a `%i`
otherwise the target file will be overwritten on every rollover as the SizeBased Triggering Policy
will not cause the timestamp value in the file name to change. When used without a time based
triggering policy the SizeBased Triggering Policy will cause the timestamp value to change.

TimeBased Triggering Policy

The `TimeBasedTriggeringPolicy` causes a rollover once the date/time
pattern no longer applies to the active file. This policy accepts an
`interval` attribute which indicates how frequently the rollover should
occur based on the time pattern and a `modulate` boolean attribute.

.TimeBasedTriggeringPolicy Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|interval |integer |How often a rollover should occur based on the most
specific time unit in the date pattern. For example, with a date pattern
with hours as the most specific item and and increment of 4 rollovers
would occur every 4 hours. The default value is 1.

|modulate |boolean |Indicates whether the interval should be adjusted to
cause the next rollover to occur on the interval boundary. For example,
if the item is hours, the current hour is 3 am and the interval is 4
then the first rollover will occur at 4 am and then next ones will occur
at 8 am, noon, 4pm, etc. The default value is false.

|maxRandomDelay |integer |Indicates the maximum number of seconds to
randomly delay a rollover. By default, this is 0 which indicates no
delay. This setting is useful on servers where multiple applications are
configured to rollover log files at the same time and can spread the
load of doing so across time.
|=======================================================================

[#RolloverStrategies]
== RolloverStrategies

[#Rollover]
===== Rollover Strategies

[#DefaultRolloverStrategy]
== DefaultRolloverStrategy

Default Rollover Strategy

The default rollover strategy accepts both a date/time pattern and an
integer from the filePattern attribute specified on the
RollingFileAppender itself. If the date/time pattern is present it will
be replaced with the current date and time values. If the pattern
contains an integer it will be incremented on each rollover. If the
pattern contains both a date/time and integer in the pattern the integer
will be incremented until the result of the date/time pattern changes.
If the file pattern ends with ".gz", ".zip", ".bz2", ".deflate",
".pack200", or ".xz" the resulting archive will be compressed using the
compression scheme that matches the suffix. The formats bzip2, Deflate,
Pack200 and XZ require
http://commons.apache.org/proper/commons-compress/[Apache Commons
Compress]. In addition, XZ requires http://tukaani.org/xz/java.html[XZ
for Java]. The pattern may also contain lookup references that can be
resolved at runtime such as is shown in the example below.

The default rollover strategy supports three variations for incrementing
the counter. To illustrate how it works, suppose that the min attribute 
is set to 1, the max attribute is set to 3, the file name is "foo.log", 
and the file name pattern is "foo-%i.log".

[cols=",,,",options="header",]
|=======================================================================
|Number of rollovers |Active output target |Archived log files
|Description
|0 |foo.log |- |All logging is going to the initial file.

|1 |foo.log |foo-1.log |During the first rollover foo.log is renamed to
foo-1.log. A new foo.log file is created and starts being written to.

|2 |foo.log |foo-2.log, foo-1.log |During the second rollover foo.log is
renamed to foo-2.log. A new foo.log file is created and starts being
written to.

|3 |foo.log |foo-3.log, foo-2.log, foo-1.log |During the third rollover
foo.log is renamed to foo-3.log. A new foo.log file is created and
starts being written to.

|4 |foo.log |foo-3.log, foo-2.log, foo-1.log |In the fourth and
subsequent rollovers, foo-1.log is deleted, foo-2.log is renamed to
foo-1.log, foo-3.log is renamed to foo-2.log and foo.log is renamed to
foo-3.log. A new foo.log file is created and starts being written to.
|=======================================================================

By way of contrast, when the fileIndex attribute is set to "min" but all
the other settings are the same the "fixed window" strategy will be 
performed.

[cols=",,,",options="header",]
|=======================================================================
|Number of rollovers |Active output target |Archived log files
|Description
|0 |foo.log |- |All logging is going to the initial file.

|1 |foo.log |foo-1.log |During the first rollover foo.log is renamed to
foo-1.log. A new foo.log file is created and starts being written to.

|2 |foo.log |foo-1.log, foo-2.log |During the second rollover foo-1.log
is renamed to foo-2.log and foo.log is renamed to foo-1.log. A new
foo.log file is created and starts being written to.

|3 |foo.log |foo-1.log, foo-2.log, foo-3.log |During the third rollover
foo-2.log is renamed to foo-3.log, foo-1.log is renamed to foo-2.log and
foo.log is renamed to foo-1.log. A new foo.log file is created and
starts being written to.

|4 |foo.log |foo-1.log, foo-2.log, foo-3.log |In the fourth and
subsequent rollovers, foo-3.log is deleted, foo-2.log is renamed to
foo-3.log, foo-1.log is renamed to foo-2.log and foo.log is renamed to
foo-1.log. A new foo.log file is created and starts being written to.
|=======================================================================

Finally, as of release 2.8, if the fileIndex attribute is set to "nomax"
then the min and max values will be ignored and file numbering will
increment by 1 and each rollover will have an incrementally higher value
with no maximum number of files.

.DefaultRolloverStrategy Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|fileIndex |String |If set to "max" (the default), files with a higher
index will be newer than files with a smaller index. If set to "min",
file renaming and the counter will follow the Fixed Window strategy
described above.

|min |integer |The minimum value of the counter. The default value is 1.

|max |integer |The maximum value of the counter. Once this values is
reached older archives will be deleted on subsequent rollovers. The
default value is 7.

|compressionLevel |integer |Sets the compression level, 0-9, where 0 =
none, 1 = best speed, through 9 = best compression. Only implemented for
ZIP files.

|tempCompressedFilePattern |String |The pattern of the file name of the
archived log file during compression.
|=======================================================================

[#DirectWriteRolloverStrategy]
== DirectWriteRolloverStrategy

DirectWrite Rollover Strategy

The DirectWriteRolloverStrategy causes log events to be written directly
to files represented by the file pattern. With this strategy file
renames are not performed. If the size-based triggering policy causes
multiple files to be written during the specified time period they will
be numbered starting at one and continually incremented until a
time-based rollover occurs.

Warning: If the file pattern has a suffix indicating compression should
take place the current file will not be compressed when the application
is shut down. Furthermore, if the time changes such that the file
pattern no longer matches the current file it will not be compressed at
startup either.

.DirectWriteRolloverStrategy Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|maxFiles |String |The maximum number of files to allow in the time
period matching the file pattern. If the number of files is exceeded the
oldest file will be deleted. If specified, the value must be greater
than 1. If the value is less than zero or omitted then the number of
files will not be limited.

|compressionLevel |integer |Sets the compression level, 0-9, where 0 =
none, 1 = best speed, through 9 = best compression. Only implemented for
ZIP files.

|tempCompressedFilePattern |String |The pattern of the file name of the
archived log file during compression.
|=======================================================================

Below is a sample configuration that uses a RollingFileAppender with
both the time and size based triggering policies, will create up to 7
archives on the same day (1-7) that are stored in a directory based on
the current year and month, and will compress each archive using gzip:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
----

This second example shows a rollover strategy that will keep up to 20
files before removing them.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
      <DefaultRolloverStrategy max="20"/>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
----

Below is a sample configuration that uses a RollingFileAppender with
both the time and size based triggering policies, will create up to 7
archives on the same day (1-7) that are stored in a directory based on
the current year and month, and will compress each archive using gzip
and will roll every 6 hours when the hour is divisible by 6:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy interval="6" modulate="true"/>
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
----

This sample configuration uses a RollingFileAppender with both the cron
and size based triggering policies, and writes directly to an unlimited
number of archive files. The cron trigger causes a rollover every hour
while the file size is limited to 250MB:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" filePattern="logs/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <CronTriggeringPolicy schedule="0 0 * * * ?"/>
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
----

This sample configuration is the same as the previous but limits the
number of files saved each hour to 10:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingFile name="RollingFile" filePattern="logs/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <CronTriggeringPolicy schedule="0 0 * * * ?"/>
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
      <DirectWriteRolloverStrategy maxFiles="10"/>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
----

[#CustomDeleteOnRollover]
== CustomDeleteOnRollover

Log Archive Retention Policy: Delete on Rollover

Log4j-2.5 introduces a `Delete` action that gives users more control
over what files are deleted at rollover time than what was possible with
the DefaultRolloverStrategy `max` attribute. The Delete action lets
users configure one or more conditions that select the files to delete
relative to a base directory.

Note that it is possible to delete any file, not just rolled over log
files, so use this action with care! With the `testMode` parameter you
can test your configuration without accidentally deleting the wrong
files.

.Delete Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|basePath |String |_Required._ Base path from where to start scanning
for files to delete.

|maxDepth |int |The maximum number of levels of directories to visit. A
value of 0 means that only the starting file (the base path itself) is
visited, unless denied by the security manager. A value of
Integer.MAX_VALUE indicates that all levels should be visited. The
default is 1, meaning only the files in the specified base directory.

|followLinks |boolean |Whether to follow symbolic links. Default is
false.

|testMode |boolean |If true, files are not deleted but instead a message
is printed to the link:configuration.html#StatusMessages[status logger]
at INFO level. Use this to do a dry run to test if the configuration
works as expected. Default is false.

|pathSorter |PathSorter |A plugin implementing the
link:../log4j-core/apidocs/org/apache/logging/log4j/core/appender/rolling/action/PathSorter.html[PathSorter]
interface to sort the files before selecting the files to delete. The
default is to sort most recently modified files first.

|pathConditions [[DeletePathCondition]] |PathCondition[] a|
_Required if no ScriptCondition is specified._ One or more PathCondition
elements.

If more than one condition is specified, they all need to accept a path
before it is deleted. Conditions can be nested, in which case the inner
condition(s) are evaluated only if the outer condition accepts the path.
If conditions are not nested they may be evaluated in any order.

Conditions can also be combined with the logical operators AND, OR and
NOT by using the `IfAll`, `IfAny` and `IfNot` composite conditions.

Users can create custom conditions or use the built-in conditions:

* link:#DeleteIfFileName[IfFileName] - accepts files whose path
(relative to the base path) matches a
https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html[regular
expression] or a
https://docs.oracle.com/javase/7/docs/api/java/nio/file/FileSystem.html#getPathMatcher(java.lang.String)[glob].
* link:#DeleteIfLastModified[IfLastModified] - accepts files that are as
old as or older than the specified
link:../log4j-core/apidocs/org/apache/logging/log4j/core/appender/rolling/action/Duration.html#parse(CharSequence)[duration].
* link:#DeleteIfAccumulatedFileCount[IfAccumulatedFileCount] - accepts
paths after some count threshold is exceeded during the file tree walk.
* link:#DeleteIfAccumulatedFileSize[IfAccumulatedFileSize] - accepts
paths after the accumulated file size threshold is exceeded during the
file tree walk.
* IfAll - accepts a path if all nested conditions accept it (logical
AND). Nested conditions may be evaluated in any order.
* IfAny - accepts a path if one of the nested conditions accept it
(logical OR). Nested conditions may be evaluated in any order.
* IfNot - accepts a path if the nested condition does not accept it
(logical NOT).

|scriptCondition [[DeleteScriptCondition]] |ScriptCondition a|
_Required if no PathConditions are specified._ A ScriptCondition element
specifying a script.

The ScriptCondition should contain a link:#ScriptCondition[Script,
ScriptRef or ScriptFile] element that specifies the logic to be
executed. (See also the link:filters.html#Script[ScriptFilter]
documentation for more examples of configuring ScriptFiles and
ScriptRefs.)

The script is passed a number of link:#ScriptParameters[parameters],
including a list of paths found under the base path (up to `maxDepth`)
and must return a list with the paths to delete.

|=======================================================================

[#DeleteIfFileName]
== DeleteIfFileName

.IfFileName Condition Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|glob |String |_Required if regex not specified._ Matches the relative
path (relative to the base path) using a limited pattern language that
resembles regular expressions but with a
https://docs.oracle.com/javase/7/docs/api/java/nio/file/FileSystem.html#getPathMatcher(java.lang.String)[simpler
syntax].

|regex |String |_Required if glob not specified._ Matches the relative
path (relative to the base path) using a regular expression as defined
by the
https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html[Pattern]
class.

|nestedConditions |PathCondition[] |An optional set of nested
link:#DeletePathCondition[PathConditions]. If any nested conditions
exist they all need to accept the file before it is deleted. Nested
conditions are only evaluated if the outer condition accepts a file (if
the path name matches).
|=======================================================================

[#DeleteIfLastModified]
== DeleteIfLastModified

.IfLastModified Condition Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|age |String |_Required._ Specifies a
link:../log4j-core/apidocs/org/apache/logging/log4j/core/appender/rolling/action/Duration.html#parse(CharSequence)[duration].
The condition accepts files that are as old or older than the specified
duration.

|nestedConditions |PathCondition[] |An optional set of nested
link:#DeletePathCondition[PathConditions]. If any nested conditions
exist they all need to accept the file before it is deleted. Nested
conditions are only evaluated if the outer condition accepts a file (if
the file is old enough).
|=======================================================================

[#DeleteIfAccumulatedFileCount]
== DeleteIfAccumulatedFileCount

.IfAccumulatedFileCount Condition Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|exceeds |int |_Required._ The threshold count from which files will be
deleted.

|nestedConditions |PathCondition[] |An optional set of nested
link:#DeletePathCondition[PathConditions]. If any nested conditions
exist they all need to accept the file before it is deleted. Nested
conditions are only evaluated if the outer condition accepts a file (if
the threshold count has been exceeded).
|=======================================================================

[#DeleteIfAccumulatedFileSize]
== DeleteIfAccumulatedFileSize

.IfAccumulatedFileSize Condition Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|exceeds |String |_Required._ The threshold accumulated file size from
which files will be deleted. The size can be specified in bytes, with
the suffix KB, MB or GB, for example `20MB`.

|nestedConditions |PathCondition[] |An optional set of nested
link:#DeletePathCondition[PathConditions]. If any nested conditions
exist they all need to accept the file before it is deleted. Nested
conditions are only evaluated if the outer condition accepts a file (if
the threshold accumulated file size has been exceeded).
|=======================================================================

Below is a sample configuration that uses a RollingFileAppender with the
cron triggering policy configured to trigger every day at midnight.
Archives are stored in a directory based on the current year and month.
All files under the base directory that match the "*/app-*.log.gz" glob
and are 60 days old or older are deleted at rollover time.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Properties>
    <Property name="baseDir">logs</Property>
  </Properties>
  <Appenders>
    <RollingFile name="RollingFile" fileName="${baseDir}/app.log"
          filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd}.log.gz">
      <PatternLayout pattern="%d %p %c{1.} [%t] %m%n" />
      <CronTriggeringPolicy schedule="0 0 0 * * ?"/>
      <DefaultRolloverStrategy>
        <Delete basePath="${baseDir}" maxDepth="2">
          <IfFileName glob="*/app-*.log.gz" />
          <IfLastModified age="60d" />
        </Delete>
      </DefaultRolloverStrategy>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
----

Below is a sample configuration that uses a RollingFileAppender with
both the time and size based triggering policies, will create up to 100
archives on the same day (1-100) that are stored in a directory based on
the current year and month, and will compress each archive using gzip
and will roll every hour. During every rollover, this configuration will
delete files that match "*/app-*.log.gz" and are 30 days old or older,
but keep the most recent 100 GB or the most recent 10 files, whichever
comes first.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Properties>
    <Property name="baseDir">logs</Property>
  </Properties>
  <Appenders>
    <RollingFile name="RollingFile" fileName="${baseDir}/app.log"
          filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout pattern="%d %p %c{1.} [%t] %m%n" />
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
      <DefaultRolloverStrategy max="100">
        <!--
        Nested conditions: the inner condition is only evaluated on files
        for which the outer conditions are true.
        -->
        <Delete basePath="${baseDir}" maxDepth="2">
          <IfFileName glob="*/app-*.log.gz">
            <IfLastModified age="30d">
              <IfAny>
                <IfAccumulatedFileSize exceeds="100 GB" />
                <IfAccumulatedFileCount exceeds="10" />
              </IfAny>
            </IfLastModified>
          </IfFileName>
        </Delete>
      </DefaultRolloverStrategy>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
----

[#ScriptCondition]
== ScriptCondition

.ScriptCondition Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|script |Script, ScriptFile or ScriptRef |The Script element that
specifies the logic to be executed. The script is passed a list of paths
found under the base path and must return the paths to delete as a
`java.util.List<PathWithAttributes>`. See also the
link:filters.html#Script[ScriptFilter] documentation for an example of
how ScriptFiles and ScriptRefs can be configured.
|=======================================================================

[#ScriptParameters]
== ScriptParameters

.Script Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|basePath |`java.nio.file.Path` |The directory from where the Delete
action started scanning for files to delete. Can be used to relativize
the paths in the pathList.

|pathList |`java.util.List<PathWithAttributes>` |The list of paths found
under the base path up to the specified max depth, sorted most recently
modified files first. The script is free to modify and return this list.

|statusLogger |StatusLogger |The StatusLogger that can be used to log
internal events during script execution.

|configuration |Configuration |The Configuration that owns this
ScriptCondition.

|substitutor |StrSubstitutor |The StrSubstitutor used to replace lookup
variables.

|? |String |Any properties declared in the configuration.
|=======================================================================

Below is a sample configuration that uses a RollingFileAppender with the
cron triggering policy configured to trigger every day at midnight.
Archives are stored in a directory based on the current year and month.
The script returns a list of rolled over files under the base directory
dated Friday the 13th. The Delete action will delete all files returned
by the script.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="trace" name="MyApp" packages="">
  <Properties>
    <Property name="baseDir">logs</Property>
  </Properties>
  <Appenders>
    <RollingFile name="RollingFile" fileName="${baseDir}/app.log"
          filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyyMMdd}.log.gz">
      <PatternLayout pattern="%d %p %c{1.} [%t] %m%n" />
      <CronTriggeringPolicy schedule="0 0 0 * * ?"/>
      <DefaultRolloverStrategy>
        <Delete basePath="${baseDir}" maxDepth="2">
          <ScriptCondition>
            <Script name="superstitious" language="groovy"><![CDATA[
                import java.nio.file.*;

                def result = [];
                def pattern = ~/\d*\/app-(\d*)\.log\.gz/;

                pathList.each { pathWithAttributes ->
                  def relative = basePath.relativize pathWithAttributes.path
                  statusLogger.trace 'SCRIPT: relative path=' + relative + " (base=$basePath)";

                  // remove files dated Friday the 13th

                  def matcher = pattern.matcher(relative.toString());
                  if (matcher.find()) {
                    def dateString = matcher.group(1);
                    def calendar = Date.parse("yyyyMMdd", dateString).toCalendar();
                    def friday13th = calendar.get(Calendar.DAY_OF_MONTH) [#13]
== 13 \
                                  && calendar.get(Calendar.DAY_OF_WEEK) [#Calendar]
== Calendar.FRIDAY;
                    if (friday13th) {
                      result.add pathWithAttributes;
                      statusLogger.trace 'SCRIPT: deleting path ' + pathWithAttributes;
                    }
                  }
                }
                statusLogger.trace 'SCRIPT: returning ' + result;
                result;
              ]] >
            </Script>
          </ScriptCondition>
        </Delete>
      </DefaultRolloverStrategy>
    </RollingFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>
</Configuration>
----

[#CustomPosixViewAttributeOnRollover]
== CustomPosixViewAttributeOnRollover

Log Archive File Attribute View Policy: Custom file attribute on
Rollover

Log4j-2.9 introduces a `PosixViewAttribute` action that gives users more
control over which file attribute permissions, owner and group should be
applied. The PosixViewAttribute action lets users configure one or more
conditions that select the eligible files relative to a base directory.

.PosixViewAttribute Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|basePath |String |_Required._ Base path from where to start scanning
for files to apply attributes.

|maxDepth |int |The maximum number of levels of directories to visit. A
value of 0 means that only the starting file (the base path itself) is
visited, unless denied by the security manager. A value of
Integer.MAX_VALUE indicates that all levels should be visited. The
default is 1, meaning only the files in the specified base directory.

|followLinks |boolean |Whether to follow symbolic links. Default is
false.

|pathConditions |PathCondition[] |see
link:#DeletePathCondition[DeletePathCondition]

|filePermissions |String a|
File attribute permissions in POSIX format to apply when action is
executed.

Underlying files system shall support
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/PosixFileAttributeView.html[POSIX]
file attribute view.

Examples: rw------- or rw-rw-rw- etc...

|fileOwner |String a|
File owner to define when action is executed.

Changing file's owner may be restricted for security reason and
Operation not permitted IOException thrown. Only processes with an
effective user ID equal to the user ID of the file or with appropriate
privileges may change the ownership of a file if
http://www.gnu.org/software/libc/manual/html_node/Options-for-Files.html[_POSIX_CHOWN_RESTRICTED]
is in effect for path.

Underlying files system shall support file
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/FileOwnerAttributeView.html[owner]
attribute view.

|fileGroup |String a|
File group to define when action is executed.

Underlying files system shall support
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/PosixFileAttributeView.html[POSIX]
file attribute view.

|=======================================================================

Below is a sample configuration that uses a RollingFileAppender and
defines different POSIX file attribute view for current and rolled log
files.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="trace" name="MyApp" packages="">
  <Properties>
    <Property name="baseDir">logs</Property>
  </Properties>
  <Appenders>
    <RollingFile name="RollingFile" fileName="${baseDir}/app.log"
                 filePattern="${baseDir}/$${date:yyyy-MM}/app-%d{yyyyMMdd}.log.gz"
                 filePermissions="rw-------">
      <PatternLayout pattern="%d %p %c{1.} [%t] %m%n" />
      <CronTriggeringPolicy schedule="0 0 0 * * ?"/>
      <DefaultRolloverStrategy stopCustomActionsOnError="true">
        <PosixViewAttribute basePath="${baseDir}/$${date:yyyy-MM}" filePermissions="r--r--r--">
            <IfFileName glob="*.gz" />
        </PosixViewAttribute>
      </DefaultRolloverStrategy>
    </RollingFile>
  </Appenders>

  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingFile"/>
    </Root>
  </Loggers>

</Configuration>
----

[#RollingRandomAccessFileAppender]
== RollingRandomAccessFileAppender

The RollingRandomAccessFileAppender is similar to the standard
link:#RollingFileAppender[RollingFileAppender] except it is always
buffered (this cannot be switched off) and internally it uses a
`ByteBuffer + RandomAccessFile` instead of a `BufferedOutputStream`. We
saw a 20-200% performance improvement compared to RollingFileAppender
with "bufferedIO=true" in our
link:../performance.html#whichAppender[measurements]. The
RollingRandomAccessFileAppender writes to the File named in the fileName
parameter and rolls the file over according the TriggeringPolicy and the
RolloverPolicy. Similar to the RollingFileAppender,
RollingRandomAccessFileAppender uses a RollingRandomAccessFileManager to
actually perform the file I/O and perform the rollover. While
RollingRandomAccessFileAppender from different Configurations cannot be
shared, the RollingRandomAccessFileManagers can be if the Manager is
accessible. For example, two web applications in a servlet container can
have their own configuration and safely write to the same file if Log4j
is in a ClassLoader that is common to both of them.

A RollingRandomAccessFileAppender requires a
link:#TriggeringPolicies[TriggeringPolicy] and a
link:#RolloverStrategies[RolloverStrategy]. The triggering policy
determines if a rollover should be performed while the RolloverStrategy
defines how the rollover should be done. If no RolloverStrategy is
configured, RollingRandomAccessFileAppender will use the
link:#DefaultRolloverStrategy[DefaultRolloverStrategy]. Since log4j-2.5,
a link:#CustomDeleteOnRollover[custom delete action] can be configured
in the DefaultRolloverStrategy to run at rollover.

File locking is not supported by the RollingRandomAccessFileAppender.

.RollingRandomAccessFileAppender Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|append |boolean |When true - the default, records will be appended to
the end of the file. When set to false, the file will be cleared before
new records are written.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|fileName |String |The name of the file to write to. If the file, or any
of its parent directories, do not exist, they will be created.

|filePattern |String |The pattern of the file name of the archived log
file. The format of the pattern should is dependent on the
RolloverPolicy that is used. The DefaultRolloverPolicy will accept both
a date/time pattern compatible with
https://download.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html[`SimpleDateFormat`]
and/or a %i which represents an integer counter. The pattern also
supports interpolation at runtime so any of the Lookups (such as the
link:./lookups.html#DateLookup[DateLookup] can be included in the
pattern.

|immediateFlush |boolean a|
When set to true - the default, each write will be followed by a flush.
This will guarantee the data is written to disk but could impact
performance.

Flushing after every write is only useful when using this appender with
synchronous loggers. Asynchronous loggers and appenders will
automatically flush at the end of a batch of events, even if
immediateFlush is set to false. This also guarantees the data is written
to disk but is more efficient.

|bufferSize |int |The buffer size, defaults to 262,144 bytes (256 *
1024).

|layout |Layout |The Layout to use to format the LogEvent. If no layout
is supplied the default pattern layout of "%m%n" will be used.

|name |String |The name of the Appender.

|policy |TriggeringPolicy |The policy to use to determine if a rollover
should occur.

|strategy |RolloverStrategy |The strategy to use to determine the name
and location of the archive file.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|filePermissions |String a|
File attribute permissions in POSIX format to apply whenever the file is
created.

Underlying files system shall support
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/PosixFileAttributeView.html[POSIX]
file attribute view.

Examples: `rw-------` or `rw-rw-rw-` etc...

|fileOwner |String a|
File owner to define whenever the file is created.

Changing file's owner may be restricted for security reason and
Operation not permitted IOException thrown. Only processes with an
effective user ID equal to the user ID of the file or with appropriate
privileges may change the ownership of a file if
http://www.gnu.org/software/libc/manual/html_node/Options-for-Files.html[_POSIX_CHOWN_RESTRICTED]
is in effect for path.

Underlying files system shall support file
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/FileOwnerAttributeView.html[owner]
attribute view.

|fileGroup |String a|
File group to define whenever the file is created.

Underlying files system shall support
https://docs.oracle.com/javase/7/docs/api/java/nio/file/attribute/PosixFileAttributeView.html[POSIX]
file attribute view.

|=======================================================================

[#FRFA_TriggeringPolicies]
== FRFA_TriggeringPolicies

[#Triggering]
===== Triggering Policies

See link:#TriggeringPolicies[RollingFileAppender Triggering Policies].

[#FRFA_RolloverStrategies]
== FRFA_RolloverStrategies

[#Rollover]
===== Rollover Strategies

See link:#RolloverStrategies[RollingFileAppender Rollover Strategies].

Below is a sample configuration that uses a
RollingRandomAccessFileAppender with both the time and size based
triggering policies, will create up to 7 archives on the same day (1-7)
that are stored in a directory based on the current year and month, and
will compress each archive using gzip:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingRandomAccessFile name="RollingRandomAccessFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingRandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingRandomAccessFile"/>
    </Root>
  </Loggers>
</Configuration>
----

This second example shows a rollover strategy that will keep up to 20
files before removing them.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingRandomAccessFile name="RollingRandomAccessFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{MM-dd-yyyy}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy />
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
      <DefaultRolloverStrategy max="20"/>
    </RollingRandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingRandomAccessFile"/>
    </Root>
  </Loggers>
</Configuration>
----

Below is a sample configuration that uses a
RollingRandomAccessFileAppender with both the time and size based
triggering policies, will create up to 7 archives on the same day (1-7)
that are stored in a directory based on the current year and month, and
will compress each archive using gzip and will roll every 6 hours when
the hour is divisible by 6:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <RollingRandomAccessFile name="RollingRandomAccessFile" fileName="logs/app.log"
                 filePattern="logs/$${date:yyyy-MM}/app-%d{yyyy-MM-dd-HH}-%i.log.gz">
      <PatternLayout>
        <Pattern>%d %p %c{1.} [%t] %m%n</Pattern>
      </PatternLayout>
      <Policies>
        <TimeBasedTriggeringPolicy interval="6" modulate="true"/>
        <SizeBasedTriggeringPolicy size="250 MB"/>
      </Policies>
    </RollingRandomAccessFile>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="RollingRandomAccessFile"/>
    </Root>
  </Loggers>
</Configuration>
----

[#RoutingAppender]
== RoutingAppender

The RoutingAppender evaluates LogEvents and then routes them to a
subordinate Appender. The target Appender may be an appender previously
configured and may be referenced by its name or the Appender can be
dynamically created as needed. The RoutingAppender should be configured
after any Appenders it references to allow it to shut down properly.

You can also configure a RoutingAppender with scripts: you can run a
script when the appender starts and when a route is chosen for an log
event.

.RoutingAppender Parameters
[width="100%",cols="34%,33%,33%",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|Filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|name |String |The name of the Appender.

|RewritePolicy |RewritePolicy |The RewritePolicy that will manipulate
the LogEvent.

|Routes |Routes |Contains one or more Route declarations to identify the
criteria for choosing Appenders.

|Script |Script a|
This Script runs when Log4j starts the RoutingAppender and returns a
String Route key to determine the default Route.

This script is passed the following variables:

.RoutingAppender Script Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|configuration |Configuration |The active Configuration.

|staticVariables |Map |A Map shared between all script invocations for
this appender instance. This is the same map passed to the Routes
Script.
|=======================================================================

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].
|=======================================================================

In this example, the script causes the "ServiceWindows" route to be the
default route on Windows and "ServiceOther" on all other operating
systems. Note that the List Appender is one of our test appenders, any
appender can be used, it is only used as a shorthand.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" name="RoutingTest">
  <Appenders>
    <Routing name="Routing">
      <Script name="RoutingInit" language="JavaScript"><![CDATA[
        importPackage(java.lang);
        System.getProperty("os.name").search("Windows") > -1 ? "ServiceWindows" : "ServiceOther";]]>
      </Script>
      <Routes>
        <Route key="ServiceOther">
          <List name="List1" />
        </Route>
        <Route key="ServiceWindows">
          <List name="List2" />
        </Route>
      </Routes>
    </Routing>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Routing" />
    </Root>
  </Loggers>
</Configuration>
----

[#Routes]
===== Routes

The Routes element accepts a single attribute named "pattern". The
pattern is evaluated against all the registered Lookups and the result
is used to select a Route. Each Route may be configured with a key. If
the key matches the result of evaluating the pattern then that Route
will be selected. If no key is specified on a Route then that Route is
the default. Only one Route can be configured as the default.

The Routes element may contain a Script child element. If specified, the
Script is run for each log event and returns the String Route key to
use.

You must specify either the pattern attribute or the Script element, but
not both.

Each Route must reference an Appender. If the Route contains a ref
attribute then the Route will reference an Appender that was defined in
the configuration. If the Route contains an Appender definition then an
Appender will be created within the context of the RoutingAppender and
will be reused each time a matching Appender name is referenced through
a Route.

This script is passed the following variables:

.RoutingAppender Routes Script Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|configuration |Configuration |The active Configuration.

|staticVariables |Map |A Map shared between all script invocations for
this appender instance. This is the same map passed to the Routes
Script.

|logEvent |LogEvent |The log event.
|=======================================================================

In this example, the script runs for each log event and picks a route
based on the presence of a Marker named "AUDIT".

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN" name="RoutingTest">
  <Appenders>
    <Console name="STDOUT" target="SYSTEM_OUT" />
    <Flume name="AuditLogger" compress="true">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Routing name="Routing">
      <Routes>
        <Script name="RoutingInit" language="JavaScript"><![CDATA[
          if (logEvent.getMarker() != null && logEvent.getMarker().isInstanceOf("AUDIT")) {
                return "AUDIT";
            } else if (logEvent.getContextMap().containsKey("UserId")) {
                return logEvent.getContextMap().get("UserId");
            }
            return "STDOUT";]]>
        </Script>
        <Route>
          <RollingFile
              name="Rolling-${mdc:UserId}"
              fileName="${mdc:UserId}.log"
              filePattern="${mdc:UserId}.%i.log.gz">
            <PatternLayout>
              <pattern>%d %p %c{1.} [%t] %m%n</pattern>
            </PatternLayout>
            <SizeBasedTriggeringPolicy size="500" />
          </RollingFile>
        </Route>
        <Route ref="AuditLogger" key="AUDIT"/>
        <Route ref="STDOUT" key="STDOUT"/>
      </Routes>
      <IdlePurgePolicy timeToLive="15" timeUnit="minutes"/>
    </Routing>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Routing" />
    </Root>
  </Loggers>
</Configuration>
----

[#Purge]
===== Purge Policy

The RoutingAppender can be configured with a PurgePolicy whose purpose
is to stop and remove dormant Appenders that have been dynamically
created by the RoutingAppender. Log4j currently provides the
IdlePurgePolicy as the only PurgePolicy available for cleaning up the
Appenders. The IdlePurgePolicy accepts 2 attributes; timeToLive, which
is the number of timeUnits the Appender should survive without having
any events sent to it, and timeUnit, the String representation of
java.util.concurrent.TimeUnit which is used with the timeToLive
attribute.

Below is a sample configuration that uses a RoutingAppender to route all
Audit events to a FlumeAppender and all other events will be routed to a
RollingFileAppender that captures only the specific event type. Note
that the AuditAppender was predefined while the RollingFileAppenders are
created as needed.

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Flume name="AuditLogger" compress="true">
      <Agent host="192.168.10.101" port="8800"/>
      <Agent host="192.168.10.102" port="8800"/>
      <RFC5424Layout enterpriseNumber="18060" includeMDC="true" appName="MyApp"/>
    </Flume>
    <Routing name="Routing">
      <Routes pattern="$${sd:type}">
        <Route>
          <RollingFile name="Rolling-${sd:type}" fileName="${sd:type}.log"
                       filePattern="${sd:type}.%i.log.gz">
            <PatternLayout>
              <pattern>%d %p %c{1.} [%t] %m%n</pattern>
            </PatternLayout>
            <SizeBasedTriggeringPolicy size="500" />
          </RollingFile>
        </Route>
        <Route ref="AuditLogger" key="Audit"/>
      </Routes>
      <IdlePurgePolicy timeToLive="15" timeUnit="minutes"/>
    </Routing>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Routing"/>
    </Root>
  </Loggers>
</Configuration>
----

[#SMTPAppender]
== SMTPAppender

As of Log4j 2.11.0, Simple Mail Transfer Protocol (SMTP) support has
moved from the existing module `log4j-core` to the new module
`log4j-smtp`.

Sends an e-mail when a specific logging event occurs, typically on
errors or fatal errors.

The number of logging events delivered in this e-mail depend on the
value of *BufferSize* option. The `SMTPAppender` keeps only the last
`BufferSize` logging events in its cyclic buffer. This keeps memory
requirements at a reasonable level while still delivering useful
application context. All events in the buffer are included in the email.
The buffer will contain the most recent events of level TRACE to WARN
preceding the event that triggered the email.

The default behavior is to trigger sending an email whenever an ERROR or
higher severity event is logged and to format it as HTML. The
circumstances on when the email is sent can be controlled by setting one
or more filters on the Appender. As with other Appenders, the formatting
can be controlled by specifying a Layout for the Appender.

.SMTPAppender Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |The name of the Appender.

|from |String |The email address of the sender.

|replyTo |String |The comma-separated list of reply-to email addresses.

|to |String |The comma-separated list of recipient email addresses.

|cc |String |The comma-separated list of CC email addresses.

|bcc |String |The comma-separated list of BCC email addresses.

|subject |String |The subject of the email message.

|bufferSize |integer |The maximum number of log events to be buffered
for inclusion in the message. Defaults to 512.

|layout |Layout |The Layout to use to format the LogEvent. If no layout
is supplied link:layouts.html#HTMLLayout[HTML layout] will be used.

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|smtpDebug |boolean |When set to true enables session debugging on
STDOUT. Defaults to false.

|smtpHost |String |The SMTP hostname to send to. This parameter is
required.

|smtpPassword |String |The password required to authenticate against the
SMTP server.

|smtpPort |integer |The SMTP port to send to.

|smtpProtocol |String |The SMTP transport protocol (such as "smtps",
defaults to "smtp").

|smtpUsername |String |The username required to authenticate against the
SMTP server.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].
|=======================================================================

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <SMTP name="Mail" subject="Error Log" to="errors@logging.apache.org" from="test@logging.apache.org"
          smtpHost="localhost" smtpPort="25" bufferSize="50">
    </SMTP>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="Mail"/>
    </Root>
  </Loggers>
</Configuration>
----

[#ScriptAppenderSelector]
== ScriptAppenderSelector

When the configuration is built, the `ScriptAppenderSelector` appender
calls a `Script` to compute an appender name. Log4j then creates one of
the appender named listed under `AppenderSet` using the name of the
`ScriptAppenderSelector`. After configuration, Log4j ignores the
`ScriptAppenderSelector`. Log4j only builds the one selected appender
from the configuration tree, and ignores other `AppenderSet` child
nodes.

In the following example, the script returns the name "List2". The
appender name is recorded under the name of the
`ScriptAppenderSelector`, not the name of the selected appender, in this
example, "SelectIt".

[source,prettyprint,linenums]
----
<Configuration status="WARN" name="ScriptAppenderSelectorExample">
  <Appenders>
    <ScriptAppenderSelector name="SelectIt">
      <Script language="JavaScript"><![CDATA[
        importPackage(java.lang);
        System.getProperty("os.name").search("Windows") > -1 ? "MyCustomWindowsAppender" : "MySyslogAppender";]]>
      </Script>
      <AppenderSet>
        <MyCustomWindowsAppender name="MyAppender" ... />
        <SyslogAppender name="MySyslog" ... />
      </AppenderSet>
    </ScriptAppenderSelector>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="SelectIt" />
    </Root>
  </Loggers>
</Configuration>
----

[#SocketAppender]
== SocketAppender

The `SocketAppender` is an OutputStreamAppender that writes its output
to a remote destination specified by a host and port. The data can be
sent over either TCP or UDP and can be sent in any format. You can
optionally secure communication with link:#SSL[SSL]. Note that the TCP and SSL
variants write to the socket as a stream and do not expect response from
the target destination. Due to limitations in the TCP protocol that
means that when the target server closes its connection some log events
may continue to appear to succeed until a closed connection exception
is raised, causing those events to be lost. If guaranteed delivery is
required a protocol that requires acknowledgements must be used.

.`SocketAppender` Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |The name of the Appender.

|host |String |The name or address of the system that is listening for
log events. This parameter is required.

|port |integer |The port on the host that is listening for log events.
This parameter must be specified.If the host name resolves to multiple
IP addresses the TCP and SSL variations will fail over to the next IP
address when a connection is lost.

|protocol |String |"TCP" (default), "SSL" or "UDP".

|SSL |SslConfiguration |Contains the configuration for the KeyStore and
TrustStore. See link:#SSL[SSL].

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|immediateFail |boolean |When set to true, log events will not wait to
try to reconnect and will fail immediately if the socket is not
available.

|immediateFlush |boolean |When set to true - the default, each write
will be followed by a flush. This will guarantee the data is written to
disk but could impact performance.

|bufferedIO |boolean |When true - the default, events are written to a
buffer and the data will be written to the socket when the buffer is
full or, if immediateFlush is set, when the record is written.

|bufferSize |int |When bufferedIO is true, this is the buffer size, the
default is 8192 bytes.

|layout |Layout |The Layout to use to format the LogEvent. Required,
there is no default. _New since 2.9, in previous versions
SerializedLayout was default._

|reconnectionDelayMillis |integer |If set to a value greater than 0,
after an error the SocketManager will attempt to reconnect to the server
after waiting the specified number of milliseconds. If the reconnect
fails then an exception will be thrown (which can be caught by the
application if `ignoreExceptions` is set to `false`).

|connectTimeoutMillis |integer |The connect timeout in milliseconds. The
default is 0 (infinite timeout, like Socket.connect() methods).

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].
|=======================================================================

This is an unsecured TCP configuration:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Socket name="socket" host="localhost" port="9500">
      <JsonLayout properties="true"/>
    </Socket>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="socket"/>
    </Root>
  </Loggers>
</Configuration>
----

This is a secured link:#SSL[SSL] configuration:

[source,prettyprint,linenums]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Socket name="socket" host="localhost" port="9500">
      <JsonLayout properties="true"/>
      <SSL>
        <KeyStore   location="log4j2-keystore.jks" passwordEnvironmentVariable="KEYSTORE_PASSWORD"/>
        <TrustStore location="truststore.jks"      passwordFile="${sys:user.home}/truststore.pwd"/>
      </SSL>
    </Socket>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="socket"/>
    </Root>
  </Loggers>
</Configuration>
----

[#SSL]
== SSL

Several appenders can be configured to use either a plain network
connection or a Secure Socket Layer (SSL) connection. This section
documents the parameters available for SSL configuration.

.SSL Configuration Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|protocol |String |`SSL` if omitted. See also
http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#SSLContext[Standard
names].

|KeyStore |KeyStore |Contains your private keys and certificates, and
determines which authentication credentials to send to the remote host.

|TrustStore |TrustStore |Contains the CA certificates of the remote
counterparty. Determines whether the remote authentication credentials
(and thus the connection) should be trusted.
|=======================================================================

[#KeyStore]
===== KeyStore

The keystore is meant to contain your private keys and certificates, and
determines which authentication credentials to send to the remote host.

.KeyStore Configuration Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|location |String |Path to the keystore file.

|password |char[] |Plain text password to access the keystore. Cannot be
combined with either `passwordEnvironmentVariable` or `passwordFile`.

|passwordEnvironmentVariable |String |Name of an environment variable
that holds the password. Cannot be combined with either `password` or
`passwordFile`.

|passwordFile |String |Path to a file that holds the password. Cannot be
combined with either `password` or `passwordEnvironmentVariable`.

|type |String |Optional KeyStore type, e.g. `JKS`, `PKCS12`, `PKCS11`,
`BKS`, `Windows-MY/Windows-ROOT`, `KeychainStore`, etc. The default is
JKS. See also
http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#KeyStore[Standard
types].

|keyManagerFactoryAlgorithm |String |Optional KeyManagerFactory
algorithm. The default is `SunX509`. See also
http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#KeyManagerFactory[Standard
algorithms].
|=======================================================================

[#TrustStore]
===== TrustStore

The trust store is meant to contain the CA certificates you are willing
to trust when a remote party presents its certificate. Determines
whether the remote authentication credentials (and thus the connection)
should be trusted.

In some cases, they can be one and the same store, although it is often
better practice to use distinct stores (especially when they are
file-based).

.TrustStore Configuration Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|location |String |Path to the keystore file.

|password |char[] |Plain text password to access the keystore. Cannot be
combined with either `passwordEnvironmentVariable` or `passwordFile`.

|passwordEnvironmentVariable |String |Name of an environment variable
that holds the password. Cannot be combined with either `password` or
`passwordFile`.

|passwordFile |String |Path to a file that holds the password. Cannot be
combined with either `password` or `passwordEnvironmentVariable`.

|type |String |Optional KeyStore type, e.g. `JKS`, `PKCS12`, `PKCS11`,
`BKS`, `Windows-MY/Windows-ROOT`, `KeychainStore`, etc. The default is
JKS. See also
http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#KeyStore[Standard
types].

|trustManagerFactoryAlgorithm |String |Optional TrustManagerFactory
algorithm. The default is `SunX509`. See also
http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#TrustManagerFactory[Standard
algorithms].
|=======================================================================

[#Example]
===== Example

[source,prettyprint,linenums]
----
  ...
      <SSL>
        <KeyStore   location="log4j2-keystore.jks" passwordEnvironmentVariable="KEYSTORE_PASSWORD"/>
        <TrustStore location="truststore.jks"      passwordFile="${sys:user.home}/truststore.pwd"/>
      </SSL>
  ...
----

[#SyslogAppender]
== SyslogAppender

The `SyslogAppender` is a `SocketAppender` that writes its output to a
remote destination specified by a host and port in a format that
conforms with either the BSD Syslog format or the RFC 5424 format. The
data can be sent over either TCP or UDP.

.`SyslogAppender` Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|advertise |boolean |Indicates whether the appender should be
advertised.

|appName |String |The value to use as the APP-NAME in the RFC 5424
syslog record.

|charset |String |The character set to use when converting the syslog
String to a byte array. The String must be a valid
https://download.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html[`Charset`].
If not specified, the default system Charset will be used.

|connectTimeoutMillis |integer |The connect timeout in milliseconds. The
default is 0 (infinite timeout, like Socket.connect() methods).

|enterpriseNumber |integer |The IANA enterprise number as described in
http://tools.ietf.org/html/rfc5424#section-7.2.2[RFC 5424]

|filter |Filter |A Filter to determine if the event should be handled by
this Appender. More than one Filter may be used by using a
CompositeFilter.

|facility |String |The facility is used to try to classify the message.
The facility option must be set to one of "KERN", "USER", "MAIL",
"DAEMON", "AUTH", "SYSLOG", "LPR", "NEWS", "UUCP", "CRON", "AUTHPRIV",
"FTP", "NTP", "AUDIT", "ALERT", "CLOCK", "LOCAL0", "LOCAL1", "LOCAL2",
"LOCAL3", "LOCAL4", "LOCAL5", "LOCAL6", or "LOCAL7". These values may be
specified as upper or lower case characters.

|format |String |If set to "RFC5424" the data will be formatted in
accordance with RFC 5424. Otherwise, it will be formatted as a BSD
Syslog record. Note that although BSD Syslog records are required to be
1024 bytes or shorter the SyslogLayout does not truncate them. The
RFC5424Layout also does not truncate records since the receiver must
accept records of up to 2048 bytes and may accept records that are
longer.

|host |String |The name or address of the system that is listening for
log events. This parameter is required.

|id |String |The default structured data id to use when formatting
according to RFC 5424. If the LogEvent contains a StructuredDataMessage
the id from the Message will be used instead of this value.

|ignoreExceptions |boolean |The default is `true`, causing exceptions
encountered while appending events to be internally logged and then
ignored. When set to `false` exceptions will be propagated to the
caller, instead. You must set this to `false` when wrapping this
Appender in a link:#FailoverAppender[FailoverAppender].

|immediateFail |boolean |When set to true, log events will not wait to
try to reconnect and will fail immediately if the socket is not
available.

|immediateFlush |boolean |When set to true - the default, each write
will be followed by a flush. This will guarantee the data is written to
disk but could impact performance.

|includeMDC |boolean |Indicates whether data from the ThreadContextMap
will be included in the RFC 5424 Syslog record. Defaults to true.

|Layout |Layout |A custom layout which overrides the `format` setting.

|loggerFields |List of KeyValuePairs |Allows arbitrary PatternLayout
patterns to be included as specified ThreadContext fields; no default
specified. To use, include a >LoggerFields< nested element, containing
one or more >KeyValuePair< elements. Each >KeyValuePair< must have a key
attribute, which specifies the key name which will be used to identify
the field within the MDC Structured Data element, and a value attribute,
which specifies the PatternLayout pattern to use as the value.

|mdcExcludes |String |A comma separated list of mdc keys that should be
excluded from the LogEvent. This is mutually exclusive with the
mdcIncludes attribute. This attribute only applies to RFC 5424 syslog
records.

|mdcIncludes |String |A comma separated list of mdc keys that should be
included in the FlumeEvent. Any keys in the MDC not found in the list
will be excluded. This option is mutually exclusive with the mdcExcludes
attribute. This attribute only applies to RFC 5424 syslog records.

|mdcRequired |String |A comma separated list of mdc keys that must be
present in the MDC. If a key is not present a LoggingException will be
thrown. This attribute only applies to RFC 5424 syslog records.

|mdcPrefix |String |A string that should be prepended to each MDC key in
order to distinguish it from event attributes. The default string is
"mdc:". This attribute only applies to RFC 5424 syslog records.

|messageId |String |The default value to be used in the MSGID field of
RFC 5424 syslog records.

|name |String |The name of the Appender.

|newLine |boolean |If true, a newline will be appended to the end of the
syslog record. The default is false.

|port |integer |The port on the host that is listening for log events.
This parameter must be specified.

|protocol |String |"TCP" or "UDP". This parameter is required.

|SSL |SslConfiguration |Contains the configuration for the KeyStore and
TrustStore. See link:#SSL[SSL].

|reconnectionDelayMillis |integer |If set to a value greater than 0,
after an error the SocketManager will attempt to reconnect to the server
after waiting the specified number of milliseconds. If the reconnect
fails then an exception will be thrown (which can be caught by the
application if `ignoreExceptions` is set to `false`).
|=======================================================================

A sample syslogAppender configuration that is configured with two
`SyslogAppender`s, one using the BSD format and one using RFC 5424.

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <Syslog name="bsd" host="localhost" port="514" protocol="TCP"/>
    <Syslog name="RFC5424" format="RFC5424" host="localhost" port="8514"
            protocol="TCP" appName="MyApp" includeMDC="true"
            facility="LOCAL0" enterpriseNumber="18060" newLine="true"
            messageId="Audit" id="App"/>
  </Appenders>
  <Loggers>
    <Logger name="com.mycorp" level="error">
      <AppenderRef ref="RFC5424"/>
    </Logger>
    <Root level="error">
      <AppenderRef ref="bsd"/>
    </Root>
  </Loggers>
</Configuration>
----

For link:#SSL[SSL] this appender writes its output to a remote
destination specified by a host and port over SSL in a format that
conforms with either the BSD Syslog format or the RFC 5424 format.

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="warn" name="MyApp" packages="">
  <Appenders>
    <TLSSyslog name="bsd" host="localhost" port="6514">
      <SSL>
        <KeyStore   location="log4j2-keystore.jks" passwordEnvironmentVariable="KEYSTORE_PASSWORD"/>
        <TrustStore location="truststore.jks"      passwordFile="${sys:user.home}/truststore.pwd"/>
      </SSL>
    </TLSSyslog>
  </Appenders>
  <Loggers>
    <Root level="error">
      <AppenderRef ref="bsd"/>
    </Root>
  </Loggers>
</Configuration>
----

[#JeroMQAppender]
== JeroMQAppender

As of Log4j 2.11.0, ZeroMQ/JeroMQ support has moved from the existing
module `log4j-core` to the new module `log4j-jeromq`.

The ZeroMQ appender uses the https://github.com/zeromq/jeromq[JeroMQ]
library to send log events to one or more ZeroMQ endpoints.

This is a simple JeroMQ configuration:

[source,xml]
----
<?xml version="1.0" encoding="UTF-8"?>
<Configuration name="JeroMQAppenderTest" status="TRACE">
  <Appenders>
    <JeroMQ name="JeroMQAppender">
      <Property name="endpoint">tcp://*:5556</Property>
      <Property name="endpoint">ipc://info-topic</Property>
    </JeroMQ>
  </Appenders>
  <Loggers>
    <Root level="info">
      <AppenderRef ref="JeroMQAppender"/>
    </Root>
  </Loggers>
</Configuration>
----

The table below describes all options. Please consult the JeroMQ and
ZeroMQ documentation for details.

.JeroMQ Parameters
[cols=",,",options="header",]
|=======================================================================
|Parameter Name |Type |Description
|name |String |The name of the Appender. Required.

|Layout |layout |The Layout to use to format the LogEvent. If no layout
is supplied the default pattern layout of "%m%n" will be used.

|Filters |Filter |The Filter(s) of the Appender.

|Properties |Property[] |One or more Property elements, named
`endpoint`.

|ignoreExceptions |boolean |If true, exceptions will be logged and
suppressed. If false errors will be logged and then passed to the
application.

|affinity |long |The ZMQ_AFFINITY option. Defaults to 0.

|backlog |long |The ZMQ_BACKLOG option. Defaults to 100.

|delayAttachOnConnect |boolean |The ZMQ_DELAY_ATTACH_ON_CONNECT option.
Defaults to false.

|identity |byte[] |The ZMQ_IDENTITY option. Defaults to none.

|ipv4Only |boolean |The ZMQ_IPV4ONLY option. Defaults to true.

|linger |long |The ZMQ_LINGER option. Defaults to -1.

|maxMsgSize |long |The ZMQ_MAXMSGSIZE option. Defaults to -1.

|rcvHwm |long |The ZMQ_RCVHWM option. Defaults to 1000.

|receiveBufferSize |long |The ZMQ_RCVBUF option. Defaults to 0.

|receiveTimeOut |int |The ZMQ_RCVTIMEO option. Defaults to -1.

|reconnectIVL |long |The ZMQ_RECONNECT_IVL option. Defaults to 100.

|reconnectIVLMax |long |The ZMQ_RECONNECT_IVL_MAX option. Defaults to 0.

|sendBufferSize |long |The ZMQ_SNDBUF option. Defaults to 0.

|sendTimeOut |int |The ZMQ_SNDTIMEO option. Defaults to -1.

|sndHwm |long |The ZMQ_SNDHWM option. Defaults to 1000.

|tcpKeepAlive |int |The ZMQ_TCP_KEEPALIVE option. Defaults to -1.

|tcpKeepAliveCount |long |The ZMQ_TCP_KEEPALIVE_CNT option. Defaults to
-1.

|tcpKeepAliveIdle |long |The ZMQ_TCP_KEEPALIVE_IDLE option. Defaults to
-1.

|tcpKeepAliveInterval |long |The ZMQ_TCP_KEEPALIVE_INTVL option.
Defaults to -1.

|xpubVerbose |boolean |The ZMQ_XPUB_VERBOSE option. Defaults to false.
|=======================================================================