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<article class="doc">
<h1 class="page">Migrating from Log4j 1</h1>
<div id="preamble">
<div class="sectionbody">
<div class="admonitionblock warning">
<table>
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<td class="icon">
<i class="fa icon-warning" title="Warning"></i>
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<td class="content">
<div class="paragraph">
<p><a href="http://logging.apache.org/log4j/1.x">Log4j 1</a> has <a href="https://news.apache.org/foundation/entry/apache_logging_services_project_announces">reached End of Life</a> in 2015, and is no longer supported.
Vulnerabilities reported after August 2015 against Log4j 1 are not checked and will not be fixed.
Users should <a href="#">upgrade to Log4j 2</a> to obtain security fixes.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Since Log4j 2 has been rewritten from scratch, it introduces many breaking changes to its predecessor.
Most notably:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>It uses a new package namespace (<code>org.apache.logging.log4j</code>), whereas Log4j 1 used the <code>org.apache.log4j</code> namespace,</p>
</li>
<li>
<p>It features a
<a href="manual/api.html" class="xref page">logging API</a>
which is independent of its reference implementation,</p>
</li>
<li>
<p>It uses a new more flexible
<a href="manual/configuration.html" class="xref page">configuration file format</a>,
which is <strong>incompatible</strong> with the format used by Log4j 1.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="prepare-to-migrate"><a class="anchor" href="#prepare-to-migrate"></a>Prepare to migrate</h2>
<div class="sectionbody">
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
<div class="title">Are you a library developer?</div>
<div class="paragraph">
<p>If you are developing a library, which functionality is not related to logging, you only need to rewrite the library to use Log4j 2 API.
Skip directly to <a href="#api-migration">Log4j 1 API migration</a>.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>In order to migrate your application to Log4j 2 you need to assess first how your application <strong>and</strong> its dependencies use Log4j 1.
While Log4j 1 didn&#8217;t have a formal split between a logging API and a logging backend, for the purpose of this guide, we&#8217;ll introduce the following split:</p>
</div>
<div id="log4j-1-api-methods" class="dlist">
<dl>
<dt class="hdlist1">Log4j 1 API</dt>
<dd>
<div class="paragraph">
<p>It is the part of the Log4j 1 library that produces log events, and it is the most commonly used.
The methods that are considered part of the Log4j 1 API are listed below:</p>
</div>
<table class="tableblock frame-all grid-all stretch">
<caption class="title">Table 1. Log4j 1 API methods</caption>
<colgroup>
<col style="width: 33.3333%;">
<col style="width: 66.6667%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Class name</th>
<th class="tableblock halign-left valign-top">Methods</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/MDC.html">org.apache.log4j.MDC</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">All methods</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/NDC.html">org.apache.log4j.NDC</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">All methods</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Priority.html">org.apache.log4j.Priority</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">All methods</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Level.html">org.apache.log4j.Level</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">All methods</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Category.html">org.apache.log4j.Category</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">All methods, except: methods for the
<a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/spi/AppenderAttachable.html">AppenderAttachable</a> interface, <code>callsAppenders</code> and <code>setLevel</code>.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Logger.html">org.apache.log4j.Logger</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Same as <code>Category</code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/LogManager.html">org.apache.log4j.LogManager</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">All methods</p></td>
</tr>
</tbody>
</table>
</dd>
<dt class="hdlist1">Log4j 1 Backend</dt>
<dd>
<div class="paragraph">
<p>This is the part of the logging library that consumes log events, formats them and writes to their destination.
It also allows to configure Log4j 1 programmatically.
It is usually <strong>not used</strong> in code, since the recommended way to configure Log4j 1 is through a configuration file.</p>
</div>
</dd>
</dl>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
<div class="paragraph">
<p>While it is fairly simple to check which classes and methods in the <code>org.apache.log4j</code> package are used by your own application, the task is much more complex, when it comes to your application dependencies.</p>
</div>
<div class="paragraph">
<p>All the libraries that use <strong>Log4j 1 API</strong> in their code must have a compile dependency on either
<a href="https://central.sonatype.com/artifact/log4j/log4j">log4j:log4j</a>
or its clone
<a href="https://central.sonatype.com/artifact/ch.qos.reload4j/reload4j">ch.qos.reload4j:reload4j</a>.
There are however misconfigured libraries that declare those dependencies, even if they don&#8217;t directly use Log4j 1 <strong>at all</strong>.</p>
</div>
<div class="paragraph">
<p>To distinguish between libraries that use Log4j 1 and those that don&#8217;t, you can look for the presence of other logging APIs. If a library <strong>directly</strong> depends on:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><a href="https://central.sonatype.com/artifact/commons-logging/commons-logging"><code>commons-logging:commons-logging</code></a>,</p>
</li>
<li>
<p><a href="https://central.sonatype.com/artifact/org.apache.logging.log4j/log4j-api"><code>org.apache.logging.log4j:log4j-api</code></a>,</p>
</li>
<li>
<p><a href="https://central.sonatype.com/artifact/org.slf4j/slf4j-api"><code>org.slf4j:slf4j-api</code></a>,</p>
</li>
<li>
<p><a href="https://central.sonatype.com/artifact/org.jboss.logging/jboss-logging"><code>jboss-logging</code></a>,</p>
</li>
<li>
<p>other logging APIs,</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>it is fair to assume that it uses those libraries <strong>instead</strong> of <strong>Log4j 1 API</strong>, even if it has a direct dependency on <code>log4j:log4j</code> or <code>ch.qos.reload4j:reload4j</code>.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>The following sections explain how to migrate from Log4j 1 to Log4j 2, depending on the way Log4j 1 is used in your application:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>if your application or one of its dependencies is coded against Log4j 1 API, see <a href="#api-migration">Log4j 1 API migration</a>,</p>
</li>
<li>
<p>if your application uses Log4j 1 only as logging backend, see <a href="#backend-migration">Log4j 1 Backend migration</a>.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="api-migration"><a class="anchor" href="#api-migration"></a>Log4j 1 API migration</h2>
<div class="sectionbody">
<div class="paragraph">
<p>To migrate an application that uses Log4j 1 API as logging API, the recommended approach is to modify your code.
See <a href="#api-code-migration">Migrate code from Log4j 1 API to Log4j 2 API</a> for details.</p>
</div>
<div class="paragraph">
<p>In the case one of your libraries uses Log4j 1 API or you can not modify your logging code at the moment, a Log4j 1 to Log4j 2 bridge is available.
See <a href="#api-use-bridge">Use Log4j 1 to Log4j 2 API bridge</a> for details.</p>
</div>
<div class="sect2">
<h3 id="api-code-migration"><a class="anchor" href="#api-code-migration"></a>Migrate code from Log4j 1 API to Log4j 2 API</h3>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
<div class="paragraph">
<p>You can migrate your code from Log4j 1 to Log4j 2 automatically, by using the
<a href="https://docs.openrewrite.org/recipes/java/logging/log4j/log4j1tolog4j2">Log4j1ToLog4j2</a> OpenRewrite recipe.
See
<a href="https://docs.openrewrite.org/recipes/java/logging/log4j/log4j1tolog4j2">OpenRewrite site</a> for more details.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Except the change in the package name from <code>org.apache.log4j</code> to <code>org.apache.logging.log4j</code>, most of the class and method names in Log4j 2 API are inherited from Log4j 1 API.</p>
</div>
<div class="paragraph">
<p>In order to migrate you code, you need to:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>modify the imports and types used by your application, according to the following table:</p>
<table class="tableblock frame-all grid-all stretch">
<caption class="title">Table 2. Migration of types from Log4j 1 to Log4j 2</caption>
<colgroup>
<col style="width: 50%;">
<col style="width: 50%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Migrate Log4j 1 type</th>
<th class="tableblock halign-left valign-top">to Log4j type</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/MDC.html">org.apache.log4j.MDC</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/ThreadContext.html">org.apache.logging.log4j.ThreadContext</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/NDC.html">org.apache.log4j.NDC</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/ThreadContext.html">org.apache.logging.log4j.ThreadContext</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Priority.html">org.apache.log4j.Priority</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/Level.html">org.apache.logging.log4j.Level</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Level.html">org.apache.log4j.Level</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/Level.html">org.apache.logging.log4j.Level</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Category.html">org.apache.log4j.Category</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/Logger.html">org.apache.logging.log4j.Logger</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Logger.html">org.apache.log4j.Logger</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/Logger.html">org.apache.logging.log4j.Logger</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/LogManager.html">org.apache.log4j.LogManager</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/LogManager.html">org.apache.logging.log4j.LogManager</a></code></p></td>
</tr>
</tbody>
</table>
</li>
<li>
<p>Some Log4j 1 methods were renamed or moved to a different class.
Therefore, you need to replace the following methods with their Log4j 2 API equivalents:</p>
<table class="tableblock frame-all grid-all stretch">
<caption class="title">Table 3. Migration of methods from Log4j 1 to Log4j 2</caption>
<colgroup>
<col style="width: 50%;">
<col style="width: 50%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Migrate Log4j 1 method</th>
<th class="tableblock halign-left valign-top">to Log4j method</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Logger.html#getLogger(java.lang.String)">Logger.getLogger()</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/LogManager.html#getLogger()">LogManager.getLogger()</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Logger.html#getRootLogger()">Logger.getRootLogger()</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/LogManager.html#getRootLogger()">LogManager.getRootLogger()</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Category.html#getEffectiveLevel()">Category.getEffectiveLevel()</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="javadoc/log4j-api/org/apache/logging/log4j/Logger.html#getLevel()">Logger.getLevel()</a></code></p></td>
</tr>
</tbody>
</table>
</li>
<li>
<p>Finally, some methods need specific conversion rules to be applied:</p>
<table class="tableblock frame-all grid-all stretch">
<caption class="title">Table 4. Special Log4j 1 method migration rules</caption>
<colgroup>
<col style="width: 25%;">
<col style="width: 75%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Method</th>
<th class="tableblock halign-left valign-top">Description</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/Logger.html#getLogger(java.lang.String,%20org.apache.log4j.spi.LoggerFactory)"><code>Logger.getLogger(String, LoggerFactory)</code></a></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Remove the <code>LoggerFactory</code> parameter and use one of Log4j 2&#8217;s other extension mechanisms.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/LogManager.html#shutdown()"><code>LogManager.shutdown()</code></a></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Since Log4j 2.6, an equivalent
<a href="javadoc/log4j-api/org/apache/logging/log4j/LogManager.html#shutdown()"><code>o.a.l.l.LogManager.shutdown()</code></a>
method can be used.</p>
<p class="tableblock">The utility of this method call depends upon the logging backend used with Log4j API.</p>
<p class="tableblock">The Log4j Core backend automatically adds a JVM shutdown hook on start up to perform any cleanups, so the <code>LogManager.shutdown()</code> call can be safely removed.
Starting in Log4j 2.1, you can also specify a custom
<a href="javadoc/log4j-core/org/apache/logging/log4j/core/util/ShutdownCallbackRegistry.html">ShutdownCallbackRegistry</a>.</p>
<p class="tableblock">See
<a href="manual/systemproperties.html#log4j2.shutdownCallbackRegistry" class="xref page">log4j2.shutdownCallbackRegistry</a>
for more details.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock">Non Log4j 1 API methods</p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Methods outside of those listed in <a href="#log4j-1-api-methods">[log4j-1-api-methods]</a>, such as <code>Logger.setLevel()</code> need to be replaced with a method
call specific to the logging backend used by the application.</p>
<p class="tableblock">Some third-party integrators, such as Spring Boot, provide utility methods that let you abstract the logging backend, e.g. the
<a href="https://docs.spring.io/spring-boot/api/java/org/springframework/boot/logging/LoggingSystem.html#setLogLevel(java.lang.String,org.springframework.boot.logging.LogLevel)"><code>LoggingSystem.setLogLevel()</code></a>
Spring Boot method.</p></td>
</tr>
</tbody>
</table>
</li>
</ul>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
<div class="paragraph">
<p>To prevent a performance penalty from string concatenation in disabled log statements, Log4j 1 required the use of <code>is*Enabled()</code> guards:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-java hljs" data-lang="java">if (LOGGER.isInfoEnabled()) {
LOGGER.info("Hello " + username + "!");
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>Since Log4j 2 API introduces
<a href="manual/api.html#best-practice-concat" class="xref page">parameterized logging</a>
these guards are no longer necessary and the same statement can be rewritten as:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-java hljs" data-lang="java">LOGGER.info("Hello {}!", username);</code></pre>
</div>
</div>
</td>
</tr>
</table>
</div>
</div>
<div class="sect2">
<h3 id="api-use-bridge"><a class="anchor" href="#api-use-bridge"></a><a id="APICompatibility"></a>Use Log4j 1 to Log4j 2 API bridge</h3>
<div class="paragraph">
<p>If you can not modify your application&#8217;s code or one of your dependencies is using
<a href="#log4j-1-api-methods">Log4j 1 API</a>
as logging API, you can delay the migration process by
<a href="#log4j-1-2-api-installation">installing the Log4j 1 to Log4j 2 bridge</a>.</p>
</div>
<div class="paragraph">
<p>Since forwarding Log4j 1 API calls to Log4j 2 API calls is the basic functionality of the bridge, no further configuration is required from your part.</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="backend-migration"><a class="anchor" href="#backend-migration"></a>Log4j 1 Backend migration</h2>
<div class="sectionbody">
<div class="paragraph">
<p>If your application uses Log4j 1 <strong>only</strong> as logging backend bound to another logging API, such as Apache Commons Logging (JCL) or SLF4J, you only need to:</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>Configure all logging bridges to log to Log4j 2 API instead.
This can be done by replacing the following dependencies on your application&#8217;s runtime classpath:</p>
<table class="tableblock frame-all grid-all stretch">
<caption class="title">Table 5. Dependency migration from Log4j 1 to Log4j 2</caption>
<colgroup>
<col style="width: 50%;">
<col style="width: 50%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Replace Log4j 1 dependency</th>
<th class="tableblock halign-left valign-top">with Log4j 2 dependency</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/log4j/log4j"><code>log4j:log4j</code></a></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/org.apache.logging.log4j/log4j-core"><code>org.apache.logging.log4j:log4j-core</code></a></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/ch.qos.reload4j/reload4j"><code>ch.qos.reload4j:reload4j</code></a></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/org.apache.logging.log4j/log4j-core"><code>org.apache.logging.log4j:log4j-core</code></a></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/commons-logging/commons-logging"><code>commons-logging:commons-logging</code></a></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">either upgrade to version 1.3.0 (or later)</p>
<p class="tableblock">or replace with
<a href="https://central.sonatype.com/artifact/org.apache.logging.log4j/log4j-slf4j2-impl"><code>org.apache.logging.log4j:log4j-jcl</code></a></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/org.slf4j/slf4j-log4j12"><code>org.slf4j:slf4j-log4j12</code></a></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/org.apache.logging.log4j/log4j-slf4j2-impl"><code>org.apache.logging.log4j:log4j-slf4j2-impl</code></a></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/org.slf4j/slf4j-reload4j"><code>org.slf4j:slf4j-reload4j</code></a></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://central.sonatype.com/artifact/org.apache.logging.log4j/log4j-slf4j2-impl"><code>org.apache.logging.log4j:log4j-slf4j2-impl</code></a></p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>See <a href="manual/installation.html" class="xref page">Installation</a> for more details.</p>
</div>
</li>
<li>
<p>Convert your configuration files from the Log4j 1 to the Log4j 2 configuration format.
See <a href="#configuration-file-migration">Log4j 1 Configuration file migration</a> below for more details.</p>
</li>
</ol>
</div>
<div class="sect2">
<h3 id="migrate-custom-components"><a class="anchor" href="#migrate-custom-components"></a>Migrate Log4j 1 custom components</h3>
<div class="paragraph">
<p>Since Log4j 1 offered a limited amount of appenders and layouts, over the years users implemented many <strong>custom</strong> components that offered additional features.
If you are currently using a custom Log4j 1 component you should proceed as follows:</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>Log4j 2 provides many improvements to Log4j 1 components and many new components.
Check if the feature offered by your custom component is not already available in Log4j 2.
If you can not find the feature, ask on our <a href="/support.html">support channels</a>.</p>
</li>
<li>
<p>Since Log4j 2.17.2, the Log4j 1 to Log4j 2 bridge has a limited support for using native Log4j 1 appenders and layouts.
Native Log4j 1 components can only be configured using Log4j 1 configuration files (see <a href="#ConfigurationCompatibility">Use Log4j 1 to Log4j 2 bridge</a>)
and require the <a href="#log4j-1-2-api-installation">installation of the Log4j 1 to Log4j 2 bridge</a>.</p>
<div class="admonitionblock warning">
<table>
<tr>
<td class="icon">
<i class="fa icon-warning" title="Warning"></i>
</td>
<td class="content">
<div class="paragraph">
<p>Mixing Log4j 1 and Log4j 2 components will most certainly reduce the performance of the logging system.</p>
</div>
</td>
</tr>
</table>
</div>
</li>
<li>
<p>If your Log4j 1 native component is not supported by the Log4j 1 to Log4j 2 bridge, we suggest to rewrite it directly as Log4j 2 component.
See <a href="manual/extending.html" class="xref page">Extending</a> for more details.</p>
</li>
</ol>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="configuration-file-migration"><a class="anchor" href="#configuration-file-migration"></a>Log4j 1 Configuration file migration</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="Log4j2ConfigurationFormat"><a class="anchor" href="#Log4j2ConfigurationFormat"></a>Convert configuration file from Log4j 1 to Log4j 2</h3>
<div class="paragraph">
<p>Although the Log4j 2 configuration syntax is different from that of Log4j 1, most, if not all, of the same functionality is available.</p>
</div>
<div class="admonitionblock tip">
<table>
<tr>
<td class="icon">
<i class="fa icon-tip" title="Tip"></i>
</td>
<td class="content">
<div class="paragraph">
<p>The <code>log4j-1.2-api</code> bridge contains a small utility that converts <code>log4j.properties</code> files into <code>log4j2.xml</code> file.
In order to use it you need to:</p>
</div>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>Download the <code>log4j-api</code>, <code>log4j-core</code> and <code>log4j-1.2-api</code> artifacts.
To retrieve them all at once, see the <a href="download.html" class="xref page">Download</a> page.</p>
</li>
<li>
<p>Set the <code>CLASSPATH</code> environment variable to contain the artifacts mentioned above.</p>
</li>
<li>
<p>Run</p>
</li>
</ol>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-shell hljs" data-lang="shell">java org.apache.log4j.config.Log4j1ConfigurationConverter \
--in log4j.properties --out log4j2.xml</code></pre>
</div>
</div>
</td>
</tr>
</table>
</div>
<div class="sect3">
<h4 id="configuration-interpolation"><a class="anchor" href="#configuration-interpolation"></a>Interpolation</h4>
<div class="paragraph">
<p>Log4j 1 only supports interpolation using system properties and properties from the <code>log4j.properties</code> file using the <code>${foo}</code> syntax.
Log4j 2 extended this mechanism, by introducing pluggable <a href="manual/lookups.html" class="xref page">Lookups</a>.</p>
</div>
<div class="paragraph">
<p>In order to convert a Log4j 1 configuration file that uses interpolation to a Log4j 2 configuration file, replace all occurrences of <code>${foo}</code> with <code>${sys:foo}</code>.</p>
</div>
</div>
<div class="sect3">
<h4 id="configuration-appenders"><a class="anchor" href="#configuration-appenders"></a>Appenders</h4>
<div class="paragraph">
<p>Log4j 2 contains an equivalent for most Log4j 1 appenders:</p>
</div>
<table class="tableblock frame-all grid-all stretch">
<caption class="title">Table 6. Log4j 2 equivalents of Log4j 1 appenders</caption>
<colgroup>
<col style="width: 25%;">
<col style="width: 25%;">
<col style="width: 50%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Log4j 1 appender</th>
<th class="tableblock halign-left valign-top">Log4j 2 equivalent</th>
<th class="tableblock halign-left valign-top">Notes</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/AsyncAppender.html">org.apache.log4j.AsyncAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/delegating.html#AsyncAppender" class="xref page">Async</a></code></p></td>
<td class="tableblock halign-left valign-top"></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/ConsoleAppender.html">org.apache.log4j.ConsoleAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders.html#ConsoleAppender" class="xref page">Console</a></code></p></td>
<td class="tableblock halign-left valign-top"></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/DailyRollingFileAppender.html">org.apache.log4j.DailyRollingFileAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/rolling-file.html#RollingFileAppender" class="xref page">RollingFile</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">See <a href="#rolling-file-conversion">additional steps below</a>.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/FileAppender.html">org.apache.log4j.FileAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/file.html#FileAppender" class="xref page">File</a></code></p></td>
<td class="tableblock halign-left valign-top"></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/RollingFileAppender.html">org.apache.log4j.RollingFileAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/rolling-file.html#RollingFileAppender" class="xref page">RollingFile</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">See <a href="#rolling-file-conversion">additional steps below</a>.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/jdbc/JDBCAppender.html">org.apache.log4j.jdbc.JDBCAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/database.html#JdbcAppender" class="xref page">JDBC</a></code></p></td>
<td class="tableblock halign-left valign-top"></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/net/JMSAppender.html">org.apache.log4j.net.JMSAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/message-queue.html#JmsAppender" class="xref page">JMS</a></code></p></td>
<td class="tableblock halign-left valign-top"></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/net/SocketAppender.html">org.apache.log4j.net.SocketAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/network.html#SocketAppender" class="xref page">Socket</a></code></p></td>
<td class="tableblock halign-left valign-top"></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/net/SMTPAppender.html">org.apache.log4j.net.SMTPAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/network.html#SmtpAppender" class="xref page">SMTP</a></code></p></td>
<td class="tableblock halign-left valign-top"></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/net/SyslogAppender.html">org.apache.log4j.net.SyslogAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/network.html#SyslogAppender" class="xref page">Syslog</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock">Does not support custom layouts.</p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/rewrite/RewriteAppender.html">org.apache.log4j.rewrite.RewriteAppender</a></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders/delegating.html#RewriteAppender" class="xref page">Rewrite</a></code></p></td>
<td class="tableblock halign-left valign-top"></td>
</tr>
</tbody>
</table>
<div id="rolling-file-conversion" class="paragraph">
<p>The rolling file appender in Log4j 2 is based on the
<a href="/log4j/extras/apidocs/org/apache/log4j/rolling/RollingFileAppender.html">org.apache.log4j.rolling.RollingFileAppender</a>
from
<a href="/log4j/extras/index.html">Apache&#8482; Extras for Apache Log4j&#174;</a>
and additional care must be taken to convert the Log4j 1 rolling appenders to their Log4j 2 equivalent:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Log4j 2 by default uses a different strategy to determine the index of the archived log files.
Log4j 1 always rolls the current log file (e.g. <code>app.log</code>) to a log file with index <code>1</code> (e.g. <code>app.log.1</code>).
Log4j 2 on the other hand uses the first available index (e.g. <code>app.log.42</code> if files <code>app.log.1</code> thru <code>app.log.41</code> already exist).</p>
<div class="paragraph">
<p>To use the same algorithm to determine the index of the logged file in Log4j 1 and Log4j 2, you need to configure the <code>fileIndex</code> attribute of the
<a href="manual/appenders/rolling-file.html#DefaultRolloverStrategy" class="xref page">default rollover strategy</a> to <code>min</code>.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-xml hljs" data-lang="xml">&lt;DefaultRolloverStrategy fileIndex="min"/&gt;</code></pre>
</div>
</div>
</li>
<li>
<p>The two rolling file appenders available in Log4j 1, use an implicit file pattern and triggering policy for the archived log files.
If the current log file is called <code>app.log</code>, you need to configure the Log4j 2 rolling file appender with the following <code>filePattern</code> and triggering policy configuration options:</p>
</li>
</ul>
</div>
<table class="tableblock frame-all grid-all stretch">
<caption class="title">Table 7. Rolling file appender conversion</caption>
<colgroup>
<col style="width: 50%;">
<col style="width: 25%;">
<col style="width: 25%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Log4j 1 appender</th>
<th class="tableblock halign-left valign-top">Log4j 2 <code>filePattern</code></th>
<th class="tableblock halign-left valign-top">Log4j 2 triggering policy</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>org.apache.log4j.DailyRollingFileAppender</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>app.%d{YYYY-MM-dd}</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders.html" class="xref page">TimeBasedTriggeringPolicy</a></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>org.apache.log4j.RollingFileAppender</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>app.%i</code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><a href="manual/appenders.html" class="xref page">SizeBasedTriggeringPolicy</a></code></p></td>
</tr>
</tbody>
</table>
</div>
<div class="sect3">
<h4 id="configuration-layouts"><a class="anchor" href="#configuration-layouts"></a>Layouts</h4>
<div class="paragraph">
<p>Log4j 1 layouts can be converted to Log4j 2 layouts using the following conversion rules:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1"><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/EnhancedPatternLayout.html">org.apache.log4j.EnhancedPatternLayout</a></dt>
<dd>
<p>can be converted to a
<a href="manual/layouts.html#PatternLayout" class="xref page"><code>PatternLayout</code></a>
that uses the same pattern,</p>
</dd>
<dt class="hdlist1"><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/HTMLLayout.html">org.apache.log4j.HTMLLayout</a></dt>
<dd>
<p>can be converted to an
<a href="manual/layouts.html#HTMLLayout" class="xref page"><code>HtmlLayout</code></a>.</p>
</dd>
<dt class="hdlist1"><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/PatternLayout.html">org.apache.log4j.PatternLayout</a></dt>
<dd>
<p>can be converted to a
<a href="manual/layouts.html#PatternLayout" class="xref page"><code>PatternLayout</code></a>
that uses the same pattern,</p>
</dd>
<dt class="hdlist1"><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/SimpleLayout.html">org.apache.log4j.SimpleLayout</a></dt>
<dd>
<p>can be converted to a
<a href="manual/layouts.html#PatternLayout" class="xref page"><code>PatternLayout</code></a>
that uses the <code>%p - %m%n</code> pattern,</p>
</dd>
<dt class="hdlist1"><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/TTCCLayout.html">org.apache.log4j.TTCCLayout</a></dt>
<dd>
<p>can be converted to a
<a href="manual/layouts.html#PatternLayout" class="xref page"><code>PatternLayout</code></a>
that uses the <code>%r [%t] %p %c %notEmpty{%x }- %m%n</code> pattern,</p>
</dd>
<dt class="hdlist1"><a href="https://logging.apache.org/log4j/1.x/apidocs/org/apache/log4j/xml/XMLLayout.html">org.apache.log4j.xml.XMLLayout</a></dt>
<dd>
<p>does not have an exact equivalent in Log4j 2 Core.
If backward compatibility is required, you can <a href="#log4j-1-2-api-installation">install the Log4j 1 to Log4j 2 bridge</a> and use the
<a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-layout-Log4j1XmlLayout" class="xref page"><code>Log4j1XmlLayout</code></a>
plugin.</p>
</dd>
</dl>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
<div class="paragraph">
<p>The formatting of the <code>%p</code> (when used with custom levels), <code>%x</code> and <code>%X</code> pattern converters slightly changed between Log4j 1 and Log4j 2.
If an exact backward compatibility is required, you need to <a href="#log4j-1-2-api-installation">install the Log4j 1 to Log4j 2 bridge</a> and use the following extended patterns:</p>
</div>
<table class="tableblock frame-all grid-all stretch">
<colgroup>
<col style="width: 50%;">
<col style="width: 50%;">
</colgroup>
<thead>
<tr>
<th class="tableblock halign-left valign-top">Log4j 1 pattern</th>
<th class="tableblock halign-left valign-top">Log4j 1 to Log4j 2 bridge pattern</th>
</tr>
</thead>
<tbody>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><code>%p</code></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><code>%v1Level</code></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><code>%x</code></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><code>%ndc</code></code></p></td>
</tr>
<tr>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><code>%X</code></code></p></td>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code><code>%properties</code></code></p></td>
</tr>
</tbody>
</table>
</td>
</tr>
</table>
</div>
</div>
</div>
<div class="sect2">
<h3 id="ConfigurationCompatibility"><a class="anchor" href="#ConfigurationCompatibility"></a>Use Log4j 1 to Log4j 2 bridge</h3>
<div class="paragraph">
<p>If you cannot convert your configuration files from Log4j 1 to Log4j 2, the Log4j 1 to Log4j 2 bridge can convert your configuration files at runtime.
To use this feature, you need to <a href="#log4j-1-2-api-installation">Install the Log4j 1 to Log4j 2 bridge</a> and set one of the following configuration properties:</p>
</div>
<div class="sect3">
<h4 id="log4j1.compatibility"><a class="anchor" href="#log4j1.compatibility"></a><code>log4j1.compatibility</code></h4>
<table class="tableblock frame-all grid-all stretch">
<colgroup>
<col style="width: 16.6666%;">
<col style="width: 83.3334%;">
</colgroup>
<tbody>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Env. variable</p></th>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOG4J_COMPATIBILITY</p></td>
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Type</p></th>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>boolean</code></p></td>
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Default value</p></th>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>false</code></p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>If set to <code>true</code>, Log4j 2 will:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Scan the classpath to find Log4j 1 configuration files in the following standard locations:</p>
<div class="ulist">
<ul>
<li>
<p><code>log4j-test.properties</code>,</p>
</li>
<li>
<p><code>log4j-test.xml</code>,</p>
</li>
<li>
<p><code>log4j.properties</code>,</p>
</li>
<li>
<p><code>log4j.xml</code>.</p>
</li>
</ul>
</div>
</li>
<li>
<p>(since <code>2.24.0</code>) Enable the usage of the <code>o.a.log4j.PropertyConfigurator</code> and <code>o.a.log4j.xml.DOMConfigurator</code> classes in your code.</p>
</li>
</ul>
</div>
</div>
<div class="sect3">
<h4 id="log4j.configuration"><a class="anchor" href="#log4j.configuration"></a><code>log4j.configuration</code></h4>
<table class="tableblock frame-all grid-all stretch">
<colgroup>
<col style="width: 16.6666%;">
<col style="width: 83.3334%;">
</colgroup>
<tbody>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Env. variable</p></th>
<td class="tableblock halign-left valign-top"><p class="tableblock">LOG4J_CONFIGURATION_FILE</p></td>
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Type</p></th>
<td class="tableblock halign-left valign-top"><p class="tableblock"><a href="https://docs.oracle.com/javase/8/docs/api/java/nio/file/Path.html">Path</a>
or
<a href="https://docs.oracle.com/javase/8/docs/api/java/net/URI.html">URI</a></p></td>
</tr>
<tr>
<th class="tableblock halign-left valign-top"><p class="tableblock">Default value</p></th>
<td class="tableblock halign-left valign-top"><p class="tableblock"><code>null</code></p></td>
</tr>
</tbody>
</table>
<div class="paragraph">
<p>If not <code>null</code>, Log4j 2 will try to retrieve a <strong>Log4j 1</strong> configuration file from the given location.
The configuration file name must end in <code>.properties</code> (Log4j 1 properties format) or <code>.xml</code> (Log4j 1 XML format).
See also
<a href="##limitations-of-the-log4j-1-x-bridge">limitations of Log4j 1 configuration compatibility layer</a>.</p>
</div>
</div>
<div class="sect3">
<h4 id="limitations-of-the-log4j-1-x-bridge"><a class="anchor" href="#limitations-of-the-log4j-1-x-bridge"></a><a id="Log4j1.2BridgeLimitations"></a>Limitations of runtime configuration conversion</h4>
<div class="paragraph">
<p>The support for Log4j 1 configuration files uses Log4j 2 Core plugin system and can be extended by implementing a plugin of type
<code>org.apache.log4j.builders.Builder</code>.</p>
</div>
<div class="paragraph">
<p>The Log4j 1 to Log4j 2 bridge supports out-of-the-box the following
<a href="https://logging.apache.org/log4j/1.x/index.html">Log4j 1</a>
and
<a href="/log4j/extras/index.html">Apache Extras for Log4j 1</a>
components:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1">Appenders</dt>
<dd>
<div class="ulist">
<ul>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-AsyncAppenderBuilder" class="xref page"><code>org.apache.log4j.AsyncAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-ConsoleAppenderBuilder" class="xref page"><code>org.apache.log4j.ConsoleAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-DailyRollingFileAppenderBuilder" class="xref page"><code>org.apache.log4j.DailyRollingFileAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-FileAppenderBuilder" class="xref page"><code>org.apache.log4j.FileAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-RollingFileAppenderBuilder" class="xref page"><code>org.apache.log4j.RollingFileAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-SocketAppenderBuilder" class="xref page"><code>org.apache.log4j.net.SocketAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-SyslogAppenderBuilder" class="xref page"><code>org.apache.log4j.net.SyslogAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-RewriteAppenderBuilder" class="xref page"><code>org.apache.log4j.rewrite.RewriteAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-EnhancedRollingFileAppenderBuilder" class="xref page"><code>org.apache.log4j.rolling.RollingFileAppender</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-appender-NullAppenderBuilder" class="xref page"><code>org.apache.log4j.varia.NullAppender</code></a>.</p>
</li>
</ul>
</div>
</dd>
<dt class="hdlist1">Filters</dt>
<dd>
<div class="ulist">
<ul>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-filter-DenyAllFilterBuilder" class="xref page"><code>org.apache.log4j.varia.DenyAllFilter</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-filter-LevelMatchFilterBuilder" class="xref page"><code>org.apache.log4j.varia.LevelMatchFilter</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-filter-LevelRangeFilterBuilder" class="xref page"><code>org.apache.log4j.varia.LevelRangeFilter</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-filter-StringMatchFilterBuilder" class="xref page"><code>org.apache.log4j.varia.StringMatchFilter</code></a>.</p>
</li>
</ul>
</div>
</dd>
<dt class="hdlist1">Layouts</dt>
<dd>
<div class="ulist">
<ul>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-layout-HtmlLayoutBuilder" class="xref page"><code>org.apache.log4j.HTMLLayout</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-layout-PatternLayoutBuilder" class="xref page"><code>org.apache.log4j.PatternLayout</code></a> and <code>org.apache.log4j.EnhancedPatternLayout</code>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-layout-SimpleLayoutBuilder" class="xref page"><code>org.apache.log4j.SimpleLayout</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-layout-TTCCLayoutBuilder" class="xref page"><code>org.apache.log4j.TTCCLayout</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-layout-XmlLayoutBuilder" class="xref page"><code>org.apache.log4j.xml.XMLLayout</code></a>.</p>
</li>
</ul>
</div>
</dd>
<dt class="hdlist1">Triggering policies</dt>
<dd>
<div class="ulist">
<ul>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-rolling-CompositeTriggeringPolicyBuilder" class="xref page"><code>org.apache.log4j.rolling.CompositeTriggeringPolicy</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-rolling-SizeBasedTriggeringPolicyBuilder" class="xref page"><code>org.apache.log4j.rolling.SizeBasedTriggeringPolicy</code></a>,</p>
</li>
<li>
<p><a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-rolling-TimeBasedRollingPolicyBuilder" class="xref page"><code>org.apache.log4j.rolling.TimeBasedRollingPolicy</code></a>.</p>
</li>
</ul>
</div>
</dd>
</dl>
</div>
<div class="paragraph">
<p>See
<a href="plugin-reference.html#org-apache-logging-log4j_log4j-1-2-api_org-apache-log4j-builders-Builder" class="xref page">the plugin reference</a> for a complete list.</p>
</div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="option-1-use-the-log4j-1-x-bridge-log4j-1-2-api"><a class="anchor" href="#option-1-use-the-log4j-1-x-bridge-log4j-1-2-api"></a><a id="Log4j12Bridge"></a>Log4j 1 to Log4j 2 bridge</h2>
<div class="sectionbody">
<div class="paragraph">
<p>To help users with the migration process, a Log4j 1 to Log4j 2 bridge is available.
The bridge can fulfill four separate functions:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>It forwards all <a href="#log4j-1-api-methods">Log4j 1 API</a> method calls to the Log4j 2 API.
See <a href="#api-use-bridge">how to use the bridge for Log4j 1 API migration</a> for more details.</p>
</li>
<li>
<p>Since version 2.17.2 the bridge supports the usage of some components written for Log4j 1 inside Log4j 2 Core.
See <a href="#migrate-custom-components">how to use the bridge for Log4j 1 Backend migration</a> for more details.</p>
</li>
<li>
<p>It provides limited support for programmatic configuration of Log4j 2 Core, using Log4j 1 method calls.
This functionality requires the <a href="#log4j1.compatibility"><code>log4j1.compatibility</code> configuration property</a> to be set to <code>true</code>.</p>
</li>
<li>
<p>It provides a limited support for Log4j 1 configuration file formats.
See <a href="#ConfigurationCompatibility">how to use the bridge for Log4j 1 Configuration file migration</a> for more details.</p>
</li>
</ul>
</div>
<div class="sect2">
<h3 id="log4j-1-2-api-installation"><a class="anchor" href="#log4j-1-2-api-installation"></a>Installation</h3>
<div class="paragraph">
<p>Since the Log4j 1 to Log4j 2 Bridge <strong>replaces</strong> Log4j 1 classes, it is incompatible with the following artifacts:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><a href="https://central.sonatype.com/artifact/log4j/log4j"><code>log4j:log4j</code></a></p>
</li>
<li>
<p><a href="https://central.sonatype.com/artifact/ch.qos.reload4j/reload4j"><code>ch.qos.reload4j:reload4j</code></a>,</p>
</li>
<li>
<p><a href="https://central.sonatype.com/artifact/org.slf4j/log4j-over-slf4j"><code>org.slf4j:log4j-over-slf4j</code></a></p>
</li>
</ul>
</div>
<div class="paragraph">
<p>Before installing the bridge, you need to make sure that none of the artifacts above are present in your runtime classpath.</p>
</div>
<div class="paragraph">
<p>To install the bridge, add the following dependency to your application:</p>
</div>
<div id="_tabs_1" class="openblock tabs is-sync is-loading">
<div class="content">
<div class="ulist tablist">
<ul>
<li id="_tabs_1_maven" class="tab">
<p>Maven</p>
</li>
<li id="_tabs_1_gradle" class="tab">
<p>Gradle</p>
</li>
</ul>
</div>
<div id="_tabs_1_maven--panel" class="tabpanel" aria-labelledby="_tabs_1_maven">
<div class="paragraph">
<p>We assume you use <a href="components.html#log4j-bom" class="xref page"><code>log4j-bom</code></a> for dependency management.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-xml hljs" data-lang="xml">&lt;dependency&gt;
&lt;groupId&gt;org.apache.logging.log4j&lt;/groupId&gt;
&lt;artifactId&gt;log4j-1.2-api&lt;/artifactId&gt;
&lt;scope&gt;runtime&lt;/scope&gt;
&lt;/dependency&gt;</code></pre>
</div>
</div>
</div>
<div id="_tabs_1_gradle--panel" class="tabpanel" aria-labelledby="_tabs_1_gradle">
<div class="paragraph">
<p>We assume you use <a href="components.html#log4j-bom" class="xref page"><code>log4j-bom</code></a> for dependency management.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="highlightjs highlight"><code class="language-groovy hljs" data-lang="groovy">runtimeOnly 'org.apache.logging.log4j:log4j-1.2-api'</code></pre>
</div>
</div>
</div>
</div>
</div>
</div>
<div class="sect2">
<h3 id="when-to-stop-using-the-log4j-1-x-bridge"><a class="anchor" href="#when-to-stop-using-the-log4j-1-x-bridge"></a>When to stop using the Log4j 1 to Log4j 2 bridge</h3>
<div class="paragraph">
<p>The Log4j 1 to Log4j 2 bridge is not conceived as a long term solution.
Once:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>you have migrated your logging code to use Log4j 2 API (see <a href="#api-code-migration">Migrate code from Log4j 1 API to Log4j 2 API</a>),</p>
</li>
<li>
<p>you have migrated your configuration files to use the Log4j 2 configuration format (see <a href="#configuration-file-migration">Log4j 1 Configuration file migration</a>),</p>
</li>
<li>
<p>upgraded all the dependencies that use Log4j 1 directly to newer versions that use a proper logging API (JCL, Log4j 2 API, JBoss logging, SLF4J),</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>the bridge is no longer necessary and should be removed.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
<div class="paragraph">
<p>The separation of logging APIs from logging implementations started in 2002, with the release of
<a href="https://commons.apache.org/proper/commons-logging/">Apache Commons Logging</a> (formerly known as Jakarta Commons Logging).</p>
</div>
<div class="paragraph">
<p>We are unaware of any <strong>maintained</strong> library that is currently using Log4j 1.
However, if this is your case, please contact the library maintainer and ask them to migrate to one of the available logging APIs.</p>
</div>
</td>
</tr>
</table>
</div>
</div>
</div>
</div>
</article>
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