| <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> |
| <!-- |
| Licensed to the Apache Software Foundation (ASF) under one or more |
| 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 |
| |
| http://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. |
| --> |
| <!-- Generated by Apache Maven Doxia at 2017-04-02 --> |
| <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> |
| <title>Log4j – Overview - Apache Log4j 2</title> |
| <link rel="stylesheet" href="../css/bootstrap.min.css" type="text/css" /> |
| <link rel="stylesheet" href="../css/site.css" type="text/css" /> |
| <script type="text/javascript" src="../js/jquery.min.js"></script> |
| <script type="text/javascript" src="../js/bootstrap.min.js"></script> |
| <script type="text/javascript" src="../js/prettify.min.js"></script> |
| <script type="text/javascript" src="../js/site.js"></script> |
| <meta name="author" content="Ralph Goers" /> |
| <meta name="Date-Revision-yyyymmdd" content="20170402" /> |
| <meta http-equiv="Content-Language" content="en" /> |
| |
| </head> |
| <body class="composite"> |
| <a href="https://logging.apache.org/"> |
| <img class="logo-left" src="../images/ls-logo.jpg" alt="Apache logging services logo" /> |
| </a> |
| <img class="logo-right" src="../images/logo.png" alt="Apache log4j logo" /> |
| <div class="clear"></div> |
| |
| <div class="navbar"> |
| <div class="navbar-inner"> |
| <div class="container-fluid"> |
| <a class="brand" href="https://logging.apache.org/log4j/2.x/">Apache Log4j 2 ™</a> |
| <ul class="nav"> |
| <li> |
| |
| |
| <a href="https://wiki.apache.org/logging" class="external" target="_blank" title="Logging Wiki">Logging Wiki</a> |
| </li> |
| <li> |
| |
| |
| <a href="https://www.apache.org/" class="external" target="_blank" title="Apache">Apache</a> |
| </li> |
| <li> |
| <a href="../../../" title="Logging Services">Logging Services</a> |
| </li> |
| <li> |
| |
| |
| <a href="https://analysis.apache.org/dashboard/index/org.apache.logging.log4j:log4j" class="external" target="_blank" title="Sonar">Sonar</a> |
| </li> |
| <li> |
| |
| |
| <a href="https://github.com/apache/logging-log4j2" class="external" target="_blank" title="GitHub">GitHub</a> |
| </li> |
| </ul> |
| </div> |
| </div> |
| </div> |
| |
| <div class="container-fluid"> |
| <table class="layout-table"> |
| <tr> |
| <td class="sidebar"> |
| <div class="well sidebar-nav"> |
| <ul class="nav nav-list"> |
| <li class="nav-header"><i class="icon-home"></i>Apache Log4j™ 2</li> |
| <li class="none"> |
| <a href="../index.html" title="About">About</a> |
| </li> |
| <li class="none"> |
| <a href="../download.html" title="Download">Download</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../javadoc.html" title="Javadoc">Javadoc</a> |
| </li> |
| <li class="none"> |
| <a href="../maven-artifacts.html" title="Maven, Ivy, Gradle Artifacts">Maven, Ivy, Gradle Artifacts</a> |
| </li> |
| <li class="none"> |
| <a href="../runtime-dependencies.html" title="Runtime Dependencies">Runtime Dependencies</a> |
| </li> |
| <li class="none"> |
| <a href="../changelog.html" title="Changelog">Changelog</a> |
| </li> |
| <li class="none"> |
| <a href="../faq.html" title="FAQ">FAQ</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../performance.html" title="Performance">Performance</a> |
| </li> |
| <li class="none"> |
| <a href="../articles.html" title="Articles and Tutorials">Articles and Tutorials</a> |
| </li> |
| <li class="none"> |
| <a href="../thanks.html" title="Thanks">Thanks</a> |
| </li> |
| </ul> |
| <ul class="nav nav-list"> |
| <li class="nav-header"><i class="icon-pencil"></i>For Contributors</li> |
| <li class="none"> |
| <a href="../build.html" title="Building Log4j from Source">Building Log4j from Source</a> |
| </li> |
| <li class="none"> |
| <a href="../guidelines.html" title="Guidelines">Guidelines</a> |
| </li> |
| <li class="none"> |
| <a href="../javastyle.html" title="Style Guide">Style Guide</a> |
| </li> |
| </ul> |
| <ul class="nav nav-list"> |
| <li class="nav-header"><i class="icon-book"></i>Manual</li> |
| <li class="none active"> |
| <a href="../manual/index.html" title="Introduction">Introduction</a> |
| </li> |
| <li class="none"> |
| <a href="../manual/architecture.html" title="Architecture">Architecture</a> |
| </li> |
| <li class="none"> |
| <a href="../manual/migration.html" title="Log4j 1.x Migration">Log4j 1.x Migration</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/api.html" title="API">API</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/configuration.html" title="Configuration">Configuration</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/webapp.html" title="Web Applications and JSPs">Web Applications and JSPs</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/lookups.html" title="Lookups">Lookups</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/appenders.html" title="Appenders">Appenders</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/layouts.html" title="Layouts">Layouts</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/filters.html" title="Filters">Filters</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/async.html" title="Async Loggers">Async Loggers</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/garbagefree.html" title="Garbage-free Logging">Garbage-free Logging</a> |
| </li> |
| <li class="none"> |
| <a href="../manual/jmx.html" title="JMX">JMX</a> |
| </li> |
| <li class="none"> |
| <a href="../manual/logsep.html" title="Logging Separation">Logging Separation</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/extending.html" title="Extending Log4j">Extending Log4j</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/plugins.html" title="Plugins">Plugins</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/customconfig.html" title="Programmatic Log4j Configuration">Programmatic Log4j Configuration</a> |
| </li> |
| <li class="collapsed"> |
| <a href="../manual/customloglevels.html" title="Custom Log Levels">Custom Log Levels</a> |
| </li> |
| </ul> |
| <ul class="nav nav-list"> |
| <li class="nav-header"><i class="icon-tags"></i>Legacy</li> |
| <li class="none"> |
| |
| |
| <a href="http://logging.apache.org/log4j/1.2/" class="external" target="_blank" title="Log4j 1.2">Log4j 1.2</a> |
| </li> |
| <li class="none"> |
| |
| |
| <a href="http://logging.apache.org/log4j/log4j-2.3/" class="external" target="_blank" title="Log4j 2.3">Log4j 2.3</a> |
| </li> |
| </ul> |
| <ul class="nav nav-list"> |
| <li class="nav-header"><i class="icon-cog"></i>Components</li> |
| <li class="none"> |
| <a href="../log4j-api/index.html" title="API">API</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-core/index.html" title="Implementation">Implementation</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-jcl/index.html" title="Commons Logging Bridge">Commons Logging Bridge</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-1.2-api/index.html" title="Log4j 1.2 API">Log4j 1.2 API</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-slf4j-impl/index.html" title="SLF4J Binding">SLF4J Binding</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-jul/index.html" title="JUL Adapter">JUL Adapter</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-api-scala_2.10/index.html" title="Scala 2.10 API">Scala 2.10 API</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-api-scala_2.11/index.html" title="Scala 2.11 API">Scala 2.11 API</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-to-slf4j/index.html" title="Log4j 2 to SLF4J Adapter">Log4j 2 to SLF4J Adapter</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-flume-ng/index.html" title="Apache Flume Appender">Apache Flume Appender</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-taglib/index.html" title="Log4j Tag Library">Log4j Tag Library</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-jmx-gui/index.html" title="Log4j JMX GUI">Log4j JMX GUI</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-web/index.html" title="Log4j Web Application Support">Log4j Web Application Support</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-nosql/index.html" title="Log4j NoSQL support">Log4j NoSQL support</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-iostreams/index.html" title="Log4j IO Streams">Log4j IO Streams</a> |
| </li> |
| <li class="none"> |
| <a href="../log4j-liquibase/index.html" title="Log4j Liquibase Binding">Log4j Liquibase Binding</a> |
| </li> |
| </ul> |
| <ul class="nav nav-list"> |
| <li class="nav-header"><i class="icon-info-sign"></i>Project Information</li> |
| <li class="none"> |
| <a href="../dependencies.html" title="Dependencies">Dependencies</a> |
| </li> |
| <li class="none"> |
| <a href="../dependency-convergence.html" title="Dependency Convergence">Dependency Convergence</a> |
| </li> |
| <li class="none"> |
| <a href="../dependency-management.html" title="Dependency Management">Dependency Management</a> |
| </li> |
| <li class="none"> |
| <a href="../team-list.html" title="Project Team">Project Team</a> |
| </li> |
| <li class="none"> |
| <a href="../mail-lists.html" title="Mailing Lists">Mailing Lists</a> |
| </li> |
| <li class="none"> |
| <a href="../issue-tracking.html" title="Issue Tracking">Issue Tracking</a> |
| </li> |
| <li class="none"> |
| <a href="../license.html" title="Project License">Project License</a> |
| </li> |
| <li class="none"> |
| <a href="../source-repository.html" title="Source Repository">Source Repository</a> |
| </li> |
| <li class="none"> |
| <a href="../project-summary.html" title="Project Summary">Project Summary</a> |
| </li> |
| </ul> |
| <ul class="nav nav-list"> |
| <li class="nav-header"><i class="icon-cog"></i>Project Reports</li> |
| <li class="none"> |
| <a href="../changes-report.html" title="Changes Report">Changes Report</a> |
| </li> |
| <li class="none"> |
| <a href="../jira-report.html" title="JIRA Report">JIRA Report</a> |
| </li> |
| <li class="none"> |
| <a href="../surefire-report.html" title="Surefire Report">Surefire Report</a> |
| </li> |
| <li class="none"> |
| <a href="../rat-report.html" title="RAT Report">RAT Report</a> |
| </li> |
| </ul> |
| </div> |
| <div id="poweredBy"> |
| <a href="http://maven.apache.org/" title="Built by Maven" class="poweredBy"> |
| <img class="poweredBy" alt="Built by Maven" src="../images/maven-feather.png" /> |
| </a> |
| </div> |
| </td> |
| <td class="content"> |
| <!-- Licensed to the Apache Software Foundation (ASF) under one or more |
| 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 |
| |
| http://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. --> |
| |
| <div class="section"> |
| <h2><a name="Welcome_to_Log4j_2"></a>Welcome to Log4j 2!</h2> |
| |
| <div class="section"> |
| <h3><a name="Introduction"></a>Introduction</h3> |
| |
| <p>Almost every large application includes its own logging or tracing |
| API. In conformance with this rule, the E.U. <a class="externalLink" href="http://www.semper.org">SEMPER</a> project decided to write its |
| own tracing API. This was in early 1996. After countless enhancements, |
| several incarnations and much work that API has evolved to become |
| log4j, a popular logging package for Java. The package is distributed |
| under the <a href="../LICENSE">Apache Software License</a>, a |
| fully-fledged open source license certified by the <a class="externalLink" href="http://www.opensource.org">open source</a> initiative. The |
| latest log4j version, including full-source code, class files and |
| documentation can be found at <a class="externalLink" href="http://logging.apache.org/log4j/2.x/index.html"><b>http://logging.apache.org/log4j/2.x/index.html</b></a>. |
| </p> |
| |
| |
| <p>Inserting log statements into code is a low-tech method for |
| debugging it. It may also be the only way because debuggers are not |
| always available or applicable. This is usually the case for |
| multithreaded applications and distributed applications at large.</p> |
| |
| |
| <p>Experience indicates that logging was an important component of the |
| development cycle. It offers several advantages. It provides precise |
| <i>context</i> about a run of the application. Once inserted into |
| the code, the generation of logging output requires no human |
| intervention. Moreover, log output can be saved in persistent medium |
| to be studied at a later time. In addition to its use in the |
| development cycle, a sufficiently rich logging package can also be |
| viewed as an auditing tool.</p> |
| |
| |
| <p>As Brian W. Kernighan and Rob Pike put it in their truly excellent |
| book <i>"The Practice of Programming":</i></p> |
| |
| |
| <div class="well"> |
| As personal choice, we tend not to use debuggers beyond getting a |
| stack trace or the value of a variable or two. One reason is that it |
| is easy to get lost in details of complicated data structures and |
| control flow; we find stepping through a program less productive |
| than thinking harder and adding output statements and self-checking |
| code at critical places. Clicking over statements takes longer than |
| scanning the output of judiciously-placed displays. It takes less |
| time to decide where to put print statements than to single-step to |
| the critical section of code, even assuming we know where that |
| is. More important, debugging statements stay with the program; |
| debugging sessions are transient. |
| </div> |
| |
| |
| <p>Logging does have its drawbacks. It can slow down an |
| application. If too verbose, it can cause scrolling blindness. To |
| alleviate these concerns, log4j is designed to be reliable, fast and |
| extensible. Since logging is rarely the main focus of an application, |
| the log4j API strives to be simple to understand and to use.</p> |
| </div> |
| |
| <div class="section"> |
| <h3><a name="Log4j_2"></a>Log4j 2</h3> |
| |
| <p> |
| Log4j 1.x has been widely adopted and used in many applications. However, |
| through the years development on it has slowed down. It has become more |
| difficult to maintain due to its need to be compliant with very old versions |
| of Java and became |
| <a class="externalLink" href="https://blogs.apache.org/foundation/entry/apache_logging_services_project_announces">End |
| of Life</a> in August 2015. |
| Its alternative, SLF4J/Logback made many needed improvements to the |
| framework. So why bother with Log4j 2? Here are a few of the reasons. |
| </p> |
| |
| <ol style="list-style-type: decimal"> |
| |
| <li>Log4j 2 is designed to be usable as an audit logging framework. Both Log4j |
| 1.x and Logback will lose events while reconfiguring. Log4j 2 will not. In |
| Logback, exceptions in Appenders are never visible to the application. In |
| Log4j 2 Appenders can be configured to allow the exception to percolate |
| to the application.</li> |
| |
| <li>Log4j 2 contains next-generation <a href="async.html">Asynchronous Loggers</a> based |
| on the <a class="externalLink" href="https://lmax-exchange.github.io/disruptor/">LMAX Disruptor library</a>. |
| In multi-threaded scenarios Asynchronous Loggers have 10 times higher throughput and |
| orders of magnitude lower latency than Log4j 1.x and Logback.</li> |
| |
| <li>Log4j 2 is <a href="garbagefree.html">garbage free</a> for |
| stand-alone applications, and low garbage for web applications during steady state logging. |
| This reduces pressure on the garbage collector and can give better response time performance.</li> |
| |
| <li>Log4j 2 uses a <a href="plugins.html">Plugin system</a> that makes it extremely easy to |
| <a href="extending.html">extend the framework</a> by adding new <a href="appenders.html">Appenders</a>, |
| <a href="filters.html">Filters</a>, <a href="layouts.html">Layouts</a>, <a href="lookups.html">Lookups</a>, |
| and Pattern Converters without requiring any changes to Log4j.</li> |
| |
| <li>Due to the Plugin system configuration is simpler. Entries in the configuration |
| do not require a class name to be specified.</li> |
| |
| <li>Support for <a href="customloglevels.html">custom log levels</a>. |
| Custom log levels can be defined in code or in configuration.</li> |
| |
| <li>Support for <a href="api.html#LambdaSupport">lambda expressions</a>. |
| Client code running on Java 8 can use lambda expressions to lazily construct a log message only if |
| the requested log level is enabled. Explicit level checks are not needed, resulting in cleaner code.</li> |
| |
| <li>Support for <a href="messages.html">Message objects</a>. Messages allow support for interesting and |
| complex constructs to be passed through the logging system and be efficiently |
| manipulated. Users are free to create their own |
| <tt><a href="../log4j-api/apidocs/org/apache/logging/log4j/message/Message.html">Message</a></tt> |
| types and write custom <a href="layouts.html">Layouts</a>, <a href="filters.html">Filters</a> and |
| <a href="lookups.html">Lookups</a> to manipulate them.</li> |
| |
| <li>Log4j 1.x supports Filters on Appenders. Logback added TurboFilters to allow |
| filtering of events before they are processed by a Logger. Log4j 2 supports |
| Filters that can be configured to process events before they are handled by |
| a Logger, as they are processed by a Logger or on an Appender.</li> |
| |
| <li>Many Logback Appenders do not accept a Layout and will only send data in a |
| fixed format. Most Log4j 2 Appenders accept a Layout, allowing the data to |
| be transported in any format desired.</li> |
| |
| <li>Layouts in Log4j 1.x and Logback return a String. This resulted in the problems |
| discussed at <a class="externalLink" href="http://logback.qos.ch/manual/encoders.html">Logback Encoders</a>. |
| Log4j 2 takes the simpler approach that <a href="layouts.html">Layouts</a> always return a byte array. This has |
| the advantage that it means they can be used in virtually any Appender, not just |
| the ones that write to an OutputStream.</li> |
| <!-- and coming up: ByteBuffers, too! --> |
| |
| <li>The <a href="appenders.html#SyslogAppender">Syslog Appender</a> supports both TCP and UDP as well as |
| support for the BSD syslog |
| and the <a class="externalLink" href="http://tools.ietf.org/html/rfc5424">RFC 5424</a> formats.</li> |
| |
| <li>Log4j 2 takes advantage of Java 5 concurrency support and performs locking |
| at the lowest level possible. Log4j 1.x has known deadlock issues. Many of these |
| are fixed in Logback but many Logback classes still require synchronization at |
| a fairly high level.</li> |
| |
| <li>It is an Apache Software Foundation project following the community and support |
| model used by all ASF projects. If you want to contribute or gain the right to |
| commit changes just follow the path outlined at |
| <a class="externalLink" href="http://jakarta.apache.org/site/contributing.html">Contributing</a>.</li> |
| </ol> |
| </div> |
| </div> |
| |
| |
| </td> |
| </tr> |
| </table> |
| </div> |
| |
| <div class="footer"> |
| <p>Copyright © 1999-2017 <a class="external" href="https://www.apache.org/">The Apache Software Foundation</a>. All Rights Reserved.</p> |
| <p>Apache Logging, Apache Log4j, Log4j, Apache, the Apache feather logo, and the Apache Logging project logo are trademarks of The Apache Software Foundation.</p> |
| <p>Site powered by <a class="external" href="http://getbootstrap.com/">Twitter Bootstrap</a>. Icons from <a class="external" href="http://glyphicons.com/">Glyphicons Free</a>.</p> |
| </div> |
| </div> |
| </body> |
| </html> |
