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| <!-- Licensed to the Apache Software Foundation (ASF) under one or more |
| contributor license agreements. See the NOTICE file distributed with |
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| (the "License"); you may not use this file except in compliance with |
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| |
| <div class="section"> |
| <h2><a name="Apache_Log4j_2"></a>Apache Log4j 2</h2> |
| |
| |
| <p> |
| Apache Log4j 2 is an upgrade to Log4j that provides significant improvements over its predecessor, Log4j |
| 1.x, and provides many of the improvements available in Logback while fixing some inherent problems in |
| Logback's architecture. |
| </p> |
| |
| |
| <p>Some of the features and improvements in Log4j 2 are:</p> |
| |
| |
| <dl> |
| |
| <dt>API Separation</dt> |
| |
| <dd> |
| The API for Log4j is separate from the implementation making it clear for application developers |
| which classes and methods they can use while ensuring forward compatibility. This allows the |
| Log4j team to improve the implementation safely and in a compatible manner. |
| </dd> |
| |
| <dt>Improved Performance</dt> |
| |
| <dd> |
| Log4j 2 contains next-generation Asynchronous Loggers based |
| on the LMAX Disruptor library. In multi-threaded scenarios |
| Asynchronous Loggers have 18 times higher throughput and |
| orders of magnitude lower latency than Log4j 1.x and Logback. |
| See <a href="manual/async.html#Performance">Asynchronous Logging Performance</a> |
| for details. |
| Otherwise, Log4j 2 significantly outperforms Log4j 1.x, Logback and java.util.logging, |
| especially in multi-threaded applications. |
| See <a href="performance.html">Performance</a> for more information. |
| </dd> |
| |
| <dt>Support for multiple APIs</dt> |
| |
| <dd> |
| While the Log4j 2 API will provide the best performance, Log4j 2 provides support for the |
| Log4j 1.2, SLF4J, Commons Logging and java.util.logging (JUL) APIs. |
| </dd> |
| |
| <dt>Avoid lock-in</dt> |
| |
| <dd> |
| Applications coded to the Log4j 2 API always have the option to use any SLF4J-compliant |
| library as their logger implementation with the log4j-to-slf4j adapter. |
| </dd> |
| |
| <dt>Automatic Reloading of Configurations</dt> |
| |
| <dd> |
| Like Logback, Log4j 2 can automatically reload its configuration upon modification. Unlike Logback, |
| it will do so without losing log events while reconfiguration is taking place. |
| </dd> |
| |
| <dt>Advanced Filtering</dt> |
| |
| <dd> |
| Like Logback, Log4j 2 supports filtering based on context data, markers, regular expressions, |
| and other components in the Log event. Filtering can be specified to apply to all events |
| before being passed to Loggers or as they pass through Appenders. In addition, filters can also |
| be associated with Loggers. Unlike Logback, you can use a common Filter class in any of these |
| circumstances. |
| </dd> |
| |
| <dt>Plugin Architecture</dt> |
| |
| <dd> |
| Log4j uses the plugin pattern to configure components. As such, you do not need to write code |
| to create and configure an Appender, Layout, Pattern Converter, and so on. Log4j automatically |
| recognizes plugins and uses them when a configuration references them. |
| </dd> |
| |
| <dt>Property Support</dt> |
| |
| <dd> |
| You can reference properties in a configuration, Log4j will directly replace them, or Log4j will |
| pass them to an underlying component that will dynamically resolve them. Properties come from values |
| defined in the configuration file, system properties, environment variables, the ThreadContext |
| Map, and data present in the event. Users can further customize the property providers by |
| adding their own <a href="manual/lookups.html">Lookup</a> Plugin. |
| </dd> |
| |
| <dt>Java 8 Lambda Support</dt> |
| |
| <dd> |
| Previously, if a log message was expensive to construct, you would often explicitly check if the |
| requested log level is enabled before constructing the message. |
| Client code running on Java 8 can benefit from Log4j's <a href="manual/api.html#LambdaSupport">lambda |
| support</a>. Since Log4j will not evaluate a lambda |
| expression if the requested log level is not enabled, the same effect can be achieved with less code. |
| </dd> |
| |
| <dt>Custom Log Levels</dt> |
| |
| <dd> |
| In Log4j 2, <a href="manual/customloglevels.html">custom log levels</a> can easily be defined in code |
| or in configuration. No subclassing is required. |
| </dd> |
| |
| <dt>Garbage-free</dt> |
| |
| <dd> |
| During steady state logging, Log4j 2 is <a href="manual/garbagefree.html">garbage-free</a> |
| in stand-alone applications, and low garbage in web applications. |
| This reduces pressure on the garbage collector and can give better response time performance. |
| </dd> |
| </dl> |
| |
| |
| <div class="section"> |
| <h3><a name="Documentation"></a>Documentation</h3> |
| |
| <p> |
| The Log4j 2 User's Guide is available on this <a href="manual/index.html">site</a> or as a downloadable |
| <a href="log4j-users-guide.pdf">PDF</a>. |
| </p> |
| </div> |
| |
| |
| <div class="section"> |
| <h3><a name="Requirements"></a>Requirements</h3> |
| |
| <p> |
| Log4j 2.4 and greater requires Java 7, versions 2.0-alpha1 to 2.3 required Java 6. |
| Some features require optional dependencies; the documentation for these features specifies the |
| dependencies. |
| </p> |
| </div> |
| |
| |
| <div class="section"> |
| <h3><a name="News"></a>News</h3> |
| |
| <p> |
| Log4j 2.6.1 is now available for production. The API for Log4j 2 is not compatible with Log4j 1.x, however an adapter |
| is available to allow applications to continue to use the Log4j 1.x API. Adapters are also available for |
| Apache Commons Logging and SLF4J. |
| </p> |
| |
| <p> |
| Log4j 2.6.1 is the latest release of Log4j and contains several bug fixes that were |
| found after the release of Log4j 2.6. The list of fixes can be found in the latest |
| <a href="changes-report.html#a2.6.1">changes report</a>. |
| </p> |
| |
| <p> |
| Note that subsequent to the release of Log4j 2.6 a minor source incompatibility with prior releass was |
| found due to the addition of new methods to the Logger interface. If you have code that does:</p> |
| |
| <div> |
| <pre> |
| logger.error(null, "This is the log message", throwable); |
| </pre></div> |
| |
| <p> |
| or similar with any log level you will get a compiler error saying the reference is ambiguous. To correct this either do:</p> |
| |
| <div> |
| <pre> |
| logger.error("This is the log message", throwable); |
| </pre></div> |
| |
| <p>or</p> |
| |
| <div> |
| <pre> |
| logger.error((Marker) null, "This is the log message", throwable); |
| </pre></div> |
| |
| <p>Log4j 2.6.1 maintains binary compatibility with previous releases.</p> |
| |
| </div> |
| </div> |
| |
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