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| <li id="publishDate">Last Published: 2024-03-06<span class="divider">|</span> |
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| <li id="projectVersion">Version: 2.23.1</li> |
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| <h1>Apache Log4j</h1> |
| <div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Apache Log4j is a versatile, industrial-grade Java logging framework composed of an API, its implementation, and components to assist the deployment for various use cases. |
| Log4j is <a href="https://security.googleblog.com/2021/12/apache-log4j-vulnerability.html">used by 8% of the Maven ecosystem</a> and listed as one of <a href="https://docs.google.com/spreadsheets/d/1ONZ4qeMq8xmeCHX03lIgIYE4MEXVfVL6oj05lbuXTDM/edit#gid=1024997528">the top 100 critical open source software projects</a>. |
| The project is actively maintained by a <a href="team.html">team</a> of several volunteers and <a href="support.html">support</a>ed by a big community.</p> |
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| <div class="sect1"> |
| <h2 id="links">Quick links</h2> |
| <div class="sectionbody"> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><a href="maven-artifacts.html">How can I add Log4j artifacts to my Maven/Ivy/Gradle project?</a></p> |
| </li> |
| <li> |
| <p><a href="manual/usage.html?">How can I use the Log4j API?</a></p> |
| </li> |
| <li> |
| <p><a href="manual/configuration.html">How can I configure my <code>log4j2.xml</code>?</a></p> |
| </li> |
| <li> |
| <p><a href="release-notes.html">Where are the release notes?</a></p> |
| </li> |
| <li> |
| <p><a href="support.html"><strong>I need help!</strong></a></p> |
| </li> |
| </ul> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="features">Features</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>We share below some highlights from Log4j features.</p> |
| </div> |
| <div class="dlist"> |
| <dl> |
| <dt class="hdlist1">Batteries included</dt> |
| <dd> |
| <p>Log4j bundles a rich set of components to assist various use cases.</p> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><a href="manual/appenders.html">Appenders</a> targeting files, network sockets, databases, SMTP servers, etc.</p> |
| </li> |
| <li> |
| <p><a href="manual/layouts.html">Layouts</a> that can render CSV, HTML, JSON, Syslog, etc. formatted outputs</p> |
| </li> |
| <li> |
| <p><a href="manual/filters.html">Filters</a> that can be configured using log event rates, regular expressions, scripts, time, etc.</p> |
| </li> |
| <li> |
| <p><a href="manual/lookups.html">Lookups</a> for accessing system properties, environment variables, log event fields, etc.</p> |
| </li> |
| </ul> |
| </div> |
| </dd> |
| <dt class="hdlist1">API separation</dt> |
| <dd> |
| <p>The API for Log4j (i.e., <code>log4j-api</code>) is separate from the implementation (i.e., <code>log4j-core</code>) making it clear for application developers which classes and methods they can use while ensuring forward compatibility. |
| (See <a href="manual/api-separation.html">API Separation</a> for details.) |
| The Log4j API also provides the most feature rich logging facade in the market; support for various <code>Message</code> types (<code>Object</code>, <code>Map</code>, etc.) besides plain <code>String</code>, lambda expressions, parametrized logging, markers, levels, diagnostic contexts (aka. MDC/NDC), etc. |
| Check out the <a href="manual/api.html">Java API</a>, <a href="/log4j/kotlin">Kotlin API</a>, and <a href="/log4j/scala">Scala API</a> pages for further information.</p> |
| </dd> |
| <dt class="hdlist1">No vendor lock-in</dt> |
| <dd> |
| <p>Even though the Log4j API is implemented by the Log4j at its fullest, users can choose to use another logging backend. |
| This can be achieved by either using another backend implementing the Log4j API, or forwarding Log4j API calls to another logging facade (e.g., SLF4J) and using a backend for that particular facade.</p> |
| </dd> |
| <dt class="hdlist1">Performance</dt> |
| <dd> |
| <p>When configured correctly, Log4j can deliver excelling performance without almost any burden on the Java garbage collector. |
| This is made possible via an asynchronous logger founded on the <a href="https://lmax-exchange.github.io/disruptor/">LMAX Disruptor</a> technology (having its roots in the demanding industry of financial trading) and the garbage-free features baked at hot paths. |
| Check out the <a href="performance.html">Performance</a> page for details.</p> |
| </dd> |
| <dt class="hdlist1">Extensibility</dt> |
| <dd> |
| <p>Log4j contains a fully-fledged <a href="manual/plugins.html">plugin support</a> that users can leverage to extend its functionality. |
| You can easily add your own components (layouts, appenders, filters, etc.) or customizing existing ones (e.g., adding new directives to the <a href="manual/layouts.html#PatternLayout">Pattern</a> or <a href="manual/json-template-layout.html#extending">JSON Template Layout</a>). |
| Check out the <a href="manual/extending.html">Extending Log4j</a> page.</p> |
| </dd> |
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| Apache Logging, Apache Log4j, Log4j, Apache, the Apache feather logo, and the Apache Logging project logo are trademarks of The Apache Software Foundation.</p> |
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