| <!DOCTYPE html> |
| |
| |
| <!-- |
| | Generated by Apache Maven Doxia Site Renderer 1.11.1 from target/generated-sources/site/xdoc/manual/plugins.xml at 2024-03-06 |
| | Rendered using Apache Maven Fluido Skin 1.11.2 |
| --> |
| <html xmlns="http://www.w3.org/1999/xhtml" lang="en"> |
| <head> |
| <meta charset="UTF-8" /> |
| <meta name="viewport" content="width=device-width, initial-scale=1" /> |
| <meta name="generator" content="Apache Maven Doxia Site Renderer 1.11.1" /> |
| <meta name="author" content="Ralph Goers" /> |
| <meta name="author" content="Matt Sicker" /> |
| <title>Log4j – Log4j 2 Plugins</title> |
| <link rel="stylesheet" href="../css/apache-maven-fluido-1.11.2.min.css" /> |
| <link rel="stylesheet" href="../css/site.css" /> |
| <link rel="stylesheet" href="../css/print.css" media="print" /> |
| <script src="../js/apache-maven-fluido-1.11.2.min.js"></script> |
| </head> |
| <body class="topBarDisabled"> |
| <div class="container-fluid"> |
| <header> |
| <div id="banner"> |
| <div class="pull-left"><a href="../../.." id="bannerLeft"><img src="../images/ls-logo.jpg" alt="" style="" /></a></div> |
| <div class="pull-right"><a href=".././" id="bannerRight"><img src="../images/logo.png" alt="" style="" /></a></div> |
| <div class="clear"><hr/></div> |
| </div> |
| |
| <div id="breadcrumbs"> |
| <ul class="breadcrumb"> |
| <li id="publishDate">Last Published: 2024-03-06<span class="divider">|</span> |
| </li> |
| <li id="projectVersion">Version: 2.23.1</li> |
| <li class="pull-right"><span class="divider">|</span> |
| <a href="https://github.com/apache/logging-log4j2" class="externalLink" title="GitHub">GitHub</a></li> |
| <li class="pull-right"><span class="divider">|</span> |
| <a href="../../../" title="Logging Services">Logging Services</a></li> |
| <li class="pull-right"><span class="divider">|</span> |
| <a href="https://www.apache.org/" class="externalLink" title="Apache">Apache</a></li> |
| <li class="pull-right"><a href="https://cwiki.apache.org/confluence/display/LOGGING/Log4j" class="externalLink" title="Logging Wiki">Logging Wiki</a></li> |
| </ul> |
| </div> |
| </header> |
| <div class="row-fluid"> |
| <header id="leftColumn" class="span2"> |
| <nav class="well sidebar-nav"> |
| <ul class="nav nav-list"> |
| <li class="nav-header"><img class="imageLink" src="../img/glyphicons/home.png" alt="Apache Log4j™ 2" style="border: 0;" /> Apache Log4j™ 2</li> |
| <li><a href="../index.html" title="About"><span class="none"></span>About</a></li> |
| <li><a href="../download.html" title="Download"><span class="none"></span>Download</a></li> |
| <li><a href="../support.html" title="Support"><span class="none"></span>Support</a></li> |
| <li><a href="../maven-artifacts.html" title="Maven, Ivy, Gradle Artifacts"><span class="icon-chevron-right"></span>Maven, Ivy, Gradle Artifacts</a></li> |
| <li><a href="../release-notes.html" title="Release Notes"><span class="none"></span>Release Notes</a></li> |
| <li><a href="../faq.html" title="FAQ"><span class="none"></span>FAQ</a></li> |
| <li><a href="../performance.html" title="Performance"><span class="icon-chevron-right"></span>Performance</a></li> |
| <li><a href="../articles.html" title="Articles and Tutorials"><span class="none"></span>Articles and Tutorials</a></li> |
| <li><a href="../security.html" title="Security"><span class="icon-chevron-right"></span>Security</a></li> |
| <li class="nav-header"><img class="imageLink" src="../img/glyphicons/book.png" alt="Manual" style="border: 0;" /> Manual</li> |
| <li><a href="../manual/index.html" title="Introduction"><span class="none"></span>Introduction</a></li> |
| <li><a href="../manual/architecture.html" title="Architecture"><span class="none"></span>Architecture</a></li> |
| <li><a href="../manual/api-separation.html" title="API Separation"><span class="none"></span>API Separation</a></li> |
| <li><a href="../manual/migration.html" title="Log4j 1.x Migration"><span class="icon-chevron-right"></span>Log4j 1.x Migration</a></li> |
| <li><a href="../manual/api.html" title="Java API"><span class="icon-chevron-right"></span>Java API</a></li> |
| <li><a href="../../kotlin" title="Kotlin API"><span class="none"></span>Kotlin API</a></li> |
| <li><a href="../../scala" title="Scala API"><span class="none"></span>Scala API</a></li> |
| <li><a href="../manual/configuration.html" title="Configuration"><span class="icon-chevron-right"></span>Configuration</a></li> |
| <li><a href="../manual/usage.html" title="Usage"><span class="icon-chevron-right"></span>Usage</a></li> |
| <li><a href="../manual/webapp.html" title="Web Applications and JSPs"><span class="icon-chevron-right"></span>Web Applications and JSPs</a></li> |
| <li><a href="../manual/lookups.html" title="Lookups"><span class="icon-chevron-right"></span>Lookups</a></li> |
| <li><a href="../manual/appenders.html" title="Appenders"><span class="icon-chevron-right"></span>Appenders</a></li> |
| <li><a href="../manual/layouts.html" title="Layouts"><span class="icon-chevron-right"></span>Layouts</a></li> |
| <li><a href="../manual/filters.html" title="Filters"><span class="icon-chevron-right"></span>Filters</a></li> |
| <li><a href="../manual/async.html" title="Async Loggers"><span class="icon-chevron-right"></span>Async Loggers</a></li> |
| <li><a href="../manual/garbagefree.html" title="Garbage-free Logging"><span class="icon-chevron-right"></span>Garbage-free Logging</a></li> |
| <li><a href="../manual/jmx.html" title="JMX"><span class="none"></span>JMX</a></li> |
| <li><a href="../manual/logsep.html" title="Logging Separation"><span class="none"></span>Logging Separation</a></li> |
| <li><a href="../manual/extending.html" title="Extending Log4j"><span class="icon-chevron-right"></span>Extending Log4j</a></li> |
| <li class="active"><a><span class="icon-chevron-down"></span>Plugins</a> |
| <ul class="nav nav-list"> |
| <li><a href="../manual/plugins.html#Core" title="Core"><span class="none"></span>Core</a></li> |
| <li><a href="../manual/plugins.html#Converters" title="Converters"><span class="none"></span>Converters</a></li> |
| <li><a href="../manual/plugins.html#KeyProviders" title="Key Providers"><span class="none"></span>Key Providers</a></li> |
| <li><a href="../manual/plugins.html#Lookups" title="Lookups"><span class="none"></span>Lookups</a></li> |
| <li><a href="../manual/plugins.html#TypeConverters" title="Type Converters"><span class="none"></span>Type Converters</a></li> |
| <li><a href="../manual/plugins.html#DeveloperNotes" title="Developer Notes"><span class="none"></span>Developer Notes</a></li> |
| </ul></li> |
| <li><a href="../manual/customconfig.html" title="Programmatic Log4j Configuration"><span class="icon-chevron-right"></span>Programmatic Log4j Configuration</a></li> |
| <li><a href="../manual/customloglevels.html" title="Custom Log Levels"><span class="icon-chevron-right"></span>Custom Log Levels</a></li> |
| <li class="nav-header"><img class="imageLink" src="../img/glyphicons/pencil.png" alt="For Contributors" style="border: 0;" /> For Contributors</li> |
| <li><a href="../guidelines.html" title="Guidelines"><span class="none"></span>Guidelines</a></li> |
| <li><a href="../javastyle.html" title="Style Guide"><span class="none"></span>Style Guide</a></li> |
| <li class="nav-header"><img class="imageLink" src="../img/glyphicons/cog.png" alt="Components" style="border: 0;" /> Components</li> |
| <li><a href="../log4j-api.html" title="API"><span class="none"></span>API</a></li> |
| <li><a href="../log4j-jcl.html" title="Commons Logging Bridge"><span class="none"></span>Commons Logging Bridge</a></li> |
| <li><a href="../log4j-1.2-api.html" title="Log4j 1.2 API"><span class="none"></span>Log4j 1.2 API</a></li> |
| <li><a href="../log4j-slf4j-impl.html" title="SLF4J Binding"><span class="none"></span>SLF4J Binding</a></li> |
| <li><a href="../log4j-jul.html" title="JUL Adapter"><span class="none"></span>JUL Adapter</a></li> |
| <li><a href="../log4j-jpl.html" title="JDK Platform Logger"><span class="none"></span>JDK Platform Logger</a></li> |
| <li><a href="../log4j-to-slf4j.html" title="Log4j 2 to SLF4J Adapter"><span class="none"></span>Log4j 2 to SLF4J Adapter</a></li> |
| <li><a href="../log4j-flume-ng.html" title="Apache Flume Appender"><span class="none"></span>Apache Flume Appender</a></li> |
| <li><a href="../log4j-taglib.html" title="Log4j Tag Library"><span class="none"></span>Log4j Tag Library</a></li> |
| <li><a href="../log4j-jmx-gui.html" title="Log4j JMX GUI"><span class="none"></span>Log4j JMX GUI</a></li> |
| <li><a href="../log4j-web.html" title="Log4j Web Application Support"><span class="none"></span>Log4j Web Application Support</a></li> |
| <li><a href="../log4j-jakarta-web.html" title="Log4j Jakarta Web Application Support"><span class="none"></span>Log4j Jakarta Web Application Support</a></li> |
| <li><a href="../log4j-appserver.html" title="Log4j Application Server Integration"><span class="none"></span>Log4j Application Server Integration</a></li> |
| <li><a href="../log4j-couchdb.html" title="Log4j CouchDB appender"><span class="none"></span>Log4j CouchDB appender</a></li> |
| <li><a href="../log4j-mongodb3.html" title="Log4j MongoDB3 appender"><span class="none"></span>Log4j MongoDB3 appender</a></li> |
| <li><a href="../log4j-mongodb4.html" title="Log4j MongoDB4 appender"><span class="none"></span>Log4j MongoDB4 appender</a></li> |
| <li><a href="../log4j-cassandra.html" title="Log4j Cassandra appender"><span class="none"></span>Log4j Cassandra appender</a></li> |
| <li><a href="../log4j-iostreams.html" title="Log4j IO Streams"><span class="none"></span>Log4j IO Streams</a></li> |
| <li><a href="../log4j-docker.html" title="Log4j Docker Support"><span class="none"></span>Log4j Docker Support</a></li> |
| <li><a href="../log4j-kubernetes.html" title="Log4j Kubernetes Support"><span class="none"></span>Log4j Kubernetes Support</a></li> |
| <li><a href="../log4j-spring-boot.html" title="Log4j Spring Boot"><span class="none"></span>Log4j Spring Boot</a></li> |
| <li><a href="../log4j-spring-cloud-config-client.html" title="Log4j Spring Cloud Config Client"><span class="none"></span>Log4j Spring Cloud Config Client</a></li> |
| <li class="nav-header"><img class="imageLink" src="../img/glyphicons/tag.png" alt="Related Projects" style="border: 0;" /> Related Projects</li> |
| <li><a href="../../../chainsaw/2.x/index.html" title="Chainsaw"><span class="none"></span>Chainsaw</a></li> |
| <li><a href="../../../log4cxx/latest_stable/index.html" title="Log4Cxx"><span class="none"></span>Log4Cxx</a></li> |
| <li><a href="../../../log4j-audit/latest/index.html" title="Log4j Audit"><span class="none"></span>Log4j Audit</a></li> |
| <li><a href="../../kotlin" title="Log4j Kotlin"><span class="none"></span>Log4j Kotlin</a></li> |
| <li><a href="../../scala" title="Log4j Scala"><span class="none"></span>Log4j Scala</a></li> |
| <li><a href="../../transform" title="Log4j Transform"><span class="none"></span>Log4j Transform</a></li> |
| <li><a href="../../../log4net/index.html" title="Log4Net"><span class="none"></span>Log4Net</a></li> |
| <li class="nav-header"><img class="imageLink" src="../img/glyphicons/link.png" alt="Legacy Sites" style="border: 0;" /> Legacy Sites</li> |
| <li><a href="../../log4j-2.12.4/" title="Log4j 2.12.4 - Java 7"><span class="none"></span>Log4j 2.12.4 - Java 7</a></li> |
| <li><a href="../../log4j-2.3.2/" title="Log4j 2.3.2 - Java 6"><span class="none"></span>Log4j 2.3.2 - Java 6</a></li> |
| <li><a href="../../1.2/" title="Log4j 1.2 - End of Life"><span class="none"></span>Log4j 1.2 - End of Life</a></li> |
| <li class="nav-header"><img class="imageLink" src="../img/glyphicons/info.png" alt="Project Information" style="border: 0;" /> Project Information</li> |
| <li><a href="../team.html" title="Project Team"><span class="none"></span>Project Team</a></li> |
| <li><a href="https://www.apache.org/licenses/LICENSE-2.0" class="externalLink" title="Project License"><span class="none"></span>Project License</a></li> |
| <li><a href="https://github.com/apache/logging-log4j2" class="externalLink" title="Source Repository"><span class="none"></span>Source Repository</a></li> |
| <li><a href="../runtime-dependencies.html" title="Runtime Dependencies"><span class="none"></span>Runtime Dependencies</a></li> |
| <li><a href="../javadoc.html" title="Javadoc"><span class="none"></span>Javadoc</a></li> |
| <li><a href="../thanks.html" title="Thanks"><span class="none"></span>Thanks</a></li> |
| </ul> |
| </nav> |
| <div class="well sidebar-nav"> |
| <div id="poweredBy"> |
| <div class="clear"></div> |
| <div class="clear"></div> |
| <div class="clear"></div> |
| <a href="http://maven.apache.org/" title="Built by Maven" class="poweredBy"><img class="builtBy" alt="Built by Maven" src="../images/logos/maven-feather.png" /></a> |
| </div> |
| </div> |
| </header> |
| <main id="bodyColumn" class="span10" > |
| |
| |
| <section> |
| <h2><a name="Plugins"></a>Plugins</h2> |
| <section> |
| <h3><a name="Introduction"></a>Introduction</h3> |
| <a name="Introduction"></a> |
| |
| <p> |
| Log4j 1.x allowed for extension by requiring class attributes on most of the configuration |
| declarations. In the case of some elements, notably the PatternLayout, the only way to add |
| new pattern converters was to extend the PatternLayout class and add them via code. One |
| goal of Log4j 2 is to make extending it extremely easy through the use of plugins. |
| </p> |
| |
| <p> |
| In Log4j 2 a plugin is declared by adding a |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/Plugin.html" class="javadoc">@Plugin</a> |
| annotation to the class declaration. During initialization the |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/Configuration.html" class="javadoc">Configuration</a> |
| will invoke the |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/util/PluginManager.html" class="javadoc">PluginManager</a> |
| to load the built-in Log4j plugins as well as any custom plugins. The <code>PluginManager</code> locates |
| plugins by looking in five places: |
| </p> |
| |
| <ol style="list-style-type: decimal"> |
| |
| <li>Serialized plugin listing files on the classpath. These files are generated automatically during |
| the build (more details below).</li> |
| |
| <li>(OSGi only) Serialized plugin listing files in each active OSGi bundle. A <code>BundleListener</code> |
| is added on activation to continue checking new bundles after <code>log4j-core</code> has started.</li> |
| |
| <li><b>(Deprecated)</b> A comma-separated list of packages specified by the <code>log4j.plugin.packages</code> |
| system property.</li> |
| |
| <li><b>(Deprecated)</b> Packages passed to the static <code>PluginManager.addPackages</code> method (before Log4j configuration |
| occurs).</li> |
| |
| <li><b>(Deprecated)</b> The <a href="./configuration.html#ConfigurationSyntax">packages</a> declared in your log4j2 |
| configuration file.</li> |
| </ol> |
| |
| <p> |
| If multiple Plugins specify the same (case-insensitive) <code>name</code>, then the load order above |
| determines which one will be used. For example, to override the <code>File</code> plugin which is provided |
| by the built-in <code>FileAppender</code> class, you would need to place your plugin in a JAR file in the |
| CLASSPATH ahead of<code>log4j-core.jar</code>. This is not recommended; plugin name collisions will cause a |
| warning to be emitted. Note that in an OSGi environment, the order that bundles are scanned for plugins |
| generally follows the same order that bundles were installed into the framework. See |
| <a class="javadoc" href="https://www.osgi.org/javadoc/r5/core/org/osgi/framework/BundleContext.html#getBundles()">getBundles()</a> |
| and |
| <a class="javadoc" href="https://www.osgi.org/javadoc/r5/core/org/osgi/framework/SynchronousBundleListener.html">SynchronousBundleListener</a>. |
| In short, name collisions are even more unpredictable in an OSGi environment. |
| |
| </p> |
| |
| <p> |
| Serialized plugin listing files are generated by an annotation processor contained in the |
| log4j-core artifact which will automatically scan your code for Log4j 2 plugins and output a metadata |
| file in your processed classes. There is nothing extra that needs to be done to enable this; the Java |
| compiler will automatically pick up the annotation processor on the class path unless you explicitly |
| disable it. In that case, it would be important to add another compiler pass to your build process that |
| only handles annotation processing using the Log4j 2 annotation processor class, |
| <code>org.apache.logging.log4j.core.config.plugins.processor.PluginProcessor</code>. To do this using |
| Apache Maven, add the following execution to your <i>maven-compiler-plugin</i> (version 2.2 or higher) |
| build plugin: |
| </p> |
| |
| <div> |
| <pre class="prettyprint linenums"> |
| <plugin> |
| <groupId>org.apache.maven.plugins</groupId> |
| <artifactId>maven-compiler-plugin</artifactId> |
| <version>3.1</version> |
| <executions> |
| <execution> |
| <id>log4j-plugin-processor</id> |
| <goals> |
| <goal>compile</goal> |
| </goals> |
| <phase>process-classes</phase> |
| <configuration> |
| <proc>only</proc> |
| <annotationProcessors> |
| <annotationProcessor>org.apache.logging.log4j.core.config.plugins.processor.PluginProcessor</annotationProcessor> |
| </annotationProcessors> |
| </configuration> |
| </execution> |
| </executions> |
| </plugin> |
| </pre></div> |
| |
| <p> |
| As the configuration is processed the appropriate plugins will be automatically configured and |
| initialized. Log4j 2 utilizes a few different categories of plugins which are described in the following |
| sections. |
| </p> |
| </section> |
| <section> |
| <h3><a name="Core"></a>Core</h3> |
| <a name="Core"></a> |
| |
| <p> |
| Core plugins are those that are directly represented by an element in a configuration file, such as an |
| Appender, Layout, Logger or Filter. Custom plugins that conform to the rules laid out in the next paragraph |
| may simply be referenced in the configuration, provided they are appropriate configured to be |
| loaded by the PluginManager. |
| </p> |
| |
| <p> |
| Every Core plugin must declare a static method annotated with <code>@PluginFactory</code> or |
| <code>@PluginBuilderFactory</code>. The former is used for static factory methods that provide all options |
| as method parameters, and the latter is used to construct a new <code>Builder<T></code> class whose |
| fields are used for injecting attributes and child nodes. To allow the <code>Configuration</code> to pass |
| the correct parameters to the method, every parameter to the method must be annotated as one of the following |
| attribute types. Each attribute or element annotation must include the name that must be present in the |
| configuration in order to match the configuration item to its respective parameter. For plugin builders, |
| the names of the fields will be used by default if no name is specified in the annotation. There are dozens |
| of plugins in Log4j Core that can be used as examples for more complex scenarios including hierarchical |
| builder classes (e.g., see <code>FileAppender</code>). See <a href="extending.html#Plugin_Builders">Extending |
| Log4j with Plugin Builders</a> for more details. |
| </p> |
| <section> |
| <h4><a name="Attribute_Types"></a>Attribute Types</h4> |
| |
| <dl> |
| |
| <dt><a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/PluginAttribute.html" class="javadoc">PluginAttribute</a></dt> |
| |
| <dd>The parameter must be convertible from a String using a <a href="#TypeConverters">TypeConverter</a>. |
| Most built-in types are already supported, but custom <code>TypeConverter</code> plugins may also be |
| provided for more type support. Note that <code>PluginBuilderAttribute</code> can be used in builder class |
| fields as an easier way to provide default values.</dd> |
| |
| <dt><a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/PluginElement.html" class="javadoc">PluginElement</a></dt> |
| |
| <dd>The parameter may represent a complex object that itself has parameters that can be configured. |
| This also supports injecting an array of elements.</dd> |
| |
| <dt><a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/PluginConfiguration.html" class="javadoc">PluginConfiguration</a></dt> |
| |
| <dd>The current <code>Configuration</code> object will be passed to the plugin as a parameter.</dd> |
| |
| <dt><a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/PluginNode.html" class="javadoc">PluginNode</a></dt> |
| |
| <dd>The current <code>Node</code> being parsed will be passed to the plugin as a parameter.</dd> |
| |
| <dt><a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/PluginValue.html" class="javadoc">PluginValue</a></dt> |
| |
| <dd>The value of the current <code>Node</code> or its attribute named <code>value</code>.</dd> |
| </dl> |
| </section><section> |
| <h4><a name="Constraint_Validators"></a>Constraint Validators</h4> |
| |
| <p> |
| Plugin factory fields and parameters can be automatically validated at runtime using constraint validators |
| inspired by the <a class="externalLink" href="https://beanvalidation.org/">Bean Validation spec</a>. The following annotations |
| are bundled in Log4j, but custom |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/validation/ConstraintValidator.html" class="javadoc">ConstraintValidators</a> |
| can be created as well. |
| </p> |
| |
| <dl> |
| |
| <dt><a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/validation/constraints/Required.html" class="javadoc">Required</a></dt> |
| |
| <dd>This annotation validates that a value is non-empty. This covers a check for <code>null</code> as well |
| as several other scenarios: empty <code>CharSequence</code> objects, empty arrays, empty <code>Collection</code> |
| instances, and empty <code>Map</code> instances.</dd> |
| |
| <dt><a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/validation/constraints/ValidHost.html" class="javadoc">ValidHost</a></dt> |
| |
| <dd>This annotation validates that a value corresponds to a valid hostname. This uses the same validation as |
| <a class="javadoc" href="https://docs.oracle.com/javase/8/docs/api/java/net/InetAddress.html#getByName-java.lang.String-">InetAddress::getByName</a>.</dd> |
| |
| <dt><a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/validation/constraints/ValidPort.html" class="javadoc">ValidPort</a></dt> |
| |
| <dd>This annotation validates that a value corresponds to a valid port number between 0 and 65535.</dd> |
| </dl> |
| </section></section> |
| <section> |
| <h3><a name="Converters"></a>Converters</h3> |
| <a name="Converters"></a> |
| |
| <p> |
| Converters are used by |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/layout/PatternLayout.html" class="javadoc">PatternLayout</a> |
| to render the elements identified by the conversion pattern. Every converter must specify its category as |
| "Converter" on the <code>@Plugin</code> annotation, have a static <code>newInstance</code> method that |
| accepts an array of <code>String</code>s as its only parameter and returns an instance of the Converter, and |
| must have a <code>@ConverterKeys</code> annotation present that contains the array of converter patterns |
| that will cause the Converter to be selected. Converters that are meant to handle <code>LogEvent</code>s |
| must extend the |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/layout/LogEventPatternConverter.html" class="javadoc">LogEventPatternConverter</a> |
| class and must implement a format method that accepts a <code>LogEvent</code> and a <code>StringBuilder</code> |
| as arguments. The Converter should append the result of its operation to the <code>StringBuilder</code>. |
| </p> |
| |
| <p> |
| A second type of Converter is the FileConverter - which must have "FileConverter" specified in the |
| category attribute of the <code>@Plugin</code> annotation. While similar to a <code>LogEventPatternConverter</code>, |
| instead of a single format method these Converters will have two variations; one that takes an |
| <code>Object</code> and one that takes an array of <code>Object</code>s instead of the <code>LogEvent</code>. |
| Both append to the provided <code>StringBuilder</code> in the same fashion as a <code>LogEventPatternConverter</code>. |
| These Converters are typically used by the <code>RollingFileAppender</code> to construct the name of the |
| file to log to. |
| </p> |
| |
| <p> |
| If multiple Converters specify the same <code>ConverterKeys</code>, then the load order above determines |
| which one will be used. For example, to override the <code>%date</code> converter which is provided by the |
| built-in <code>DatePatternConverter</code> class, you would need to place your plugin in a JAR file in the |
| CLASSPATH ahead of<code>log4j-core.jar</code>. This is not recommended; pattern ConverterKeys collisions |
| will cause a warning to be emitted. Try to use unique ConverterKeys for your custom pattern converters. |
| </p> |
| </section> |
| <section> |
| <h3><a name="KeyProviders"></a>KeyProviders</h3> |
| <a name="KeyProviders"></a> |
| |
| <p> |
| Some components within Log4j may provide the ability to perform data encryption. These components require |
| a secret key to perform the encryption. Applications may provide the key by creating a class that |
| implements the |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/util/SecretKeyProvider.html" class="javadoc">SecretKeyProvider</a> |
| interface. |
| </p> |
| </section> |
| <section> |
| <h3><a name="Lookups"></a>Lookups</h3> |
| <a name="Lookups"></a> |
| |
| <p> |
| Lookups are perhaps the simplest plugins of all. They must declare their type as "Lookup" on the |
| plugin annotation and must implement the |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/lookup/StrLookup.html" class="javadoc">StrLookup</a> |
| interface. They will have two methods; a |
| lookup method that accepts a String key and returns a String value and a second lookup method that |
| accepts both a LogEvent and a String key and returns a String. Lookups may be referenced by |
| specifying ${<var>name</var>:key} where <var>name</var> is the name specified in the Plugin annotation and |
| key is the name of the item to locate. |
| </p> |
| </section> |
| <section> |
| <h3><a name="TypeConverters"></a>TypeConverters</h3> |
| <a name="TypeConverters"></a> |
| |
| <p> |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/convert/TypeConverter.html" class="javadoc">TypeConverter</a>s |
| are a sort of meta-plugin used for converting strings into other types in a plugin factory method |
| parameter. Other plugins can already be injected via the <code>@PluginElement</code> annotation; now, any |
| type supported by the type conversion system can be used in a <code>@PluginAttribute</code> parameter. |
| Conversion of enum types are supported on demand and do not require custom <code>TypeConverter</code> |
| classes. A large number of built-in Java classes are already supported; see |
| <a href="../log4j-core/apidocs/org/apache/logging/log4j/core/config/plugins/convert/TypeConverters.html" class="javadoc">TypeConverters</a> |
| for a more exhaustive listing. |
| </p> |
| |
| <p> |
| Unlike other plugins, the plugin name of a <code>TypeConverter</code> is purely cosmetic. Appropriate |
| type converters are looked up via the <code>Type</code> interface rather than via <code>Class<?></code> |
| objects only. Do note that <code>TypeConverter</code> plugins must have a default constructor. |
| When multiple converters match for a type, the first will be returned. |
| If any extends from <code>Comparable<TypeConverter<?>></code>, |
| it will be used for determining the order. |
| </p> |
| </section> |
| </section> |
| <section> |
| <h2><a name="Developer_Notes"></a>Developer Notes</h2> |
| <a name="DeveloperNotes"></a> |
| |
| <p> |
| If a plugin class implements |
| <a class="javadoc" href="https://docs.oracle.com/javase/6/docs/api/java/util/Collection.html">Collection</a> or |
| <a class="javadoc" href="https://docs.oracle.com/javase/6/docs/api/java/util/Map.html">Map</a>, then no |
| factory method is used. Instead, the class is instantiated using the default constructor, and all child |
| configuration nodes are added to the <code>Collection</code> or <code>Map</code>. |
| </p> |
| </section> |
| |
| |
| </main> |
| </div> |
| </div> |
| <hr/> |
| <footer> |
| <div class="container-fluid"> |
| <div class="row-fluid"> |
| <p align="center">Copyright © 1999-2024 <a class="external" href="https://www.apache.org">The Apache Software Foundation</a>. All Rights Reserved.<br> |
| Apache Logging, Apache Log4j, Log4j, Apache, the Apache feather logo, and the Apache Logging project logo are trademarks of The Apache Software Foundation.</p> |
| </div> |
| </div> |
| </footer> |
| <script> |
| if(anchors) { |
| anchors.add(); |
| } |
| </script> |
| </body> |
| </html> |
