| <!DOCTYPE html> |
| |
| |
| <!-- |
| | Generated by Apache Maven Doxia Site Renderer 1.11.1 from target/generated-sources/site/xdoc/manual/index.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" /> |
| <title>Log4j – Overview</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 class="active"><a><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><a href="../manual/plugins.html" title="Plugins"><span class="icon-chevron-right"></span>Plugins</a></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="Welcome_to_Log4j_2.21"></a>Welcome to Log4j 2!</h2> |
| <section> |
| <h3><a name="Introduction"></a>Introduction</h3> |
| |
| <p>Almost every large application includes its own logging or tracing |
| API. In conformance with this rule, the E.U. <a class="externalLink" href="https://www.semper.org">SEMPER</a> project decided to write its |
| own tracing API. This was in early 1996. After countless enhancements, |
| several incarnations and much work that API has evolved to become |
| log4j, a popular logging package for Java. The package is distributed |
| under the <a href="../LICENSE">Apache Software License</a>, a |
| fully-fledged open source license certified by the <a class="externalLink" href="https://www.opensource.org">open source</a> initiative. The |
| latest log4j version, including full-source code, class files and |
| documentation can be found at <a class="externalLink" href="https://logging.apache.org/log4j/2.x/index.html"><b>https://logging.apache.org/log4j/2.x/index.html</b></a>. |
| </p> |
| |
| |
| <p>Inserting log statements into code is a low-tech method for |
| debugging it. It may also be the only way because debuggers are not |
| always available or applicable. This is usually the case for |
| multithreaded applications and distributed applications at large.</p> |
| |
| |
| <p>Experience indicates that logging was an important component of the |
| development cycle. It offers several advantages. It provides precise |
| <i>context</i> about a run of the application. Once inserted into |
| the code, the generation of logging output requires no human |
| intervention. Moreover, log output can be saved in persistent medium |
| to be studied at a later time. In addition to its use in the |
| development cycle, a sufficiently rich logging package can also be |
| viewed as an auditing tool.</p> |
| |
| |
| <p>As Brian W. Kernighan and Rob Pike put it in their truly excellent |
| book <i>"The Practice of Programming":</i></p> |
| |
| |
| <div class="well"> |
| As personal choice, we tend not to use debuggers beyond getting a |
| stack trace or the value of a variable or two. One reason is that it |
| is easy to get lost in details of complicated data structures and |
| control flow; we find stepping through a program less productive |
| than thinking harder and adding output statements and self-checking |
| code at critical places. Clicking over statements takes longer than |
| scanning the output of judiciously-placed displays. It takes less |
| time to decide where to put print statements than to single-step to |
| the critical section of code, even assuming we know where that |
| is. More important, debugging statements stay with the program; |
| debugging sessions are transient. |
| </div> |
| |
| |
| <p>Logging does have its drawbacks. It can slow down an |
| application. If too verbose, it can cause scrolling blindness. To |
| alleviate these concerns, log4j is designed to be reliable, fast and |
| extensible. Since logging is rarely the main focus of an application, |
| the log4j API strives to be simple to understand and to use.</p> |
| </section> |
| <section> |
| <h3><a name="Log4j_2"></a>Log4j 2</h3> |
| |
| <p> |
| Log4j 1.x has been extensively adopted and utilized across various applications. |
| Its final release occurred in 2012, and in August 2015, the announcement was made |
| that Log4j 1.x had reached its <a class="externalLink" href="https://news.apache.org/foundation/entry/apache_logging_services_project_announces">End of Life</a>. |
| </p> |
| |
| <p> |
| So, what makes upgrading to Log4j 2 a wise decision? Here are a few compelling reasons. |
| </p> |
| |
| <ol style="list-style-type: decimal"> |
| |
| <li><b>Audit Logging:</b> Log4j 2 is designed to be usable as an audit logging framework. Both Log4j |
| 1.x and Logback will lose events while reconfiguring. Log4j 2 will not. In |
| Logback, exceptions in Appenders are never visible to the application. In |
| Log4j 2 Appenders can be configured to allow the exception to percolate |
| to the application.</li> |
| |
| <li><b>Asynchronous Loggers:</b> Log4j 2 contains next-generation <a href="async.html">Asynchronous Loggers</a> based |
| on the <a class="externalLink" href="https://lmax-exchange.github.io/disruptor/">LMAX Disruptor library</a>. |
| In multithreaded scenarios Asynchronous Loggers have 10 times higher throughput and |
| orders of magnitude lower latency than Log4j 1.x and Logback.</li> |
| |
| <li><b>Garbage Free:</b> Log4j 2 is <a href="garbagefree.html">garbage free</a> for |
| stand-alone applications, and low garbage for web applications during steady state logging. |
| This reduces pressure on the garbage collector and can give better response time performance.</li> |
| |
| <li><b>Plugins:</b> Log4j 2 uses a <a href="plugins.html">Plugin system</a> that makes it extremely easy to |
| <a href="extending.html">extend the framework</a> by adding new <a href="appenders.html">Appenders</a>, |
| <a href="filters.html">Filters</a>, <a href="layouts.html">Layouts</a>, <a href="lookups.html">Lookups</a>, |
| and Pattern Converters without requiring any changes to Log4j.</li> |
| |
| <li><b>Simple Configuration:</b> Due to the Plugin system configuration is simpler. Entries in the configuration |
| do not require a class name to be specified.</li> |
| |
| <li><b>Custom Log Levels:</b> Support for <a href="customloglevels.html">custom log levels</a>. |
| Custom log levels can be defined in code or in configuration.</li> |
| |
| <li><b>Lambdas:</b> Support for <a href="api.html#LambdaSupport">lambda expressions</a>. |
| Client code running on Java 8 can use lambda expressions to lazily construct a log message only if |
| the requested log level is enabled. Explicit level checks are not needed, resulting in cleaner code.</li> |
| |
| <li><b>Messages:</b> Support for <a href="messages.html">Message objects</a>. Messages allow support for interesting and |
| complex constructs to be passed through the logging system and be efficiently |
| manipulated. Users are free to create their own |
| <code><a href="../log4j-api/apidocs/org/apache/logging/log4j/message/Message.html">Message</a></code> |
| types and write custom <a href="layouts.html">Layouts</a>, <a href="filters.html">Filters</a> and |
| <a href="lookups.html">Lookups</a> to manipulate them.</li> |
| |
| <li><b>Filters:</b> Log4j 1.x supports Filters on Appenders. Logback added TurboFilters to allow |
| filtering of events before they are processed by a Logger. Log4j 2 supports |
| Filters that can be configured to process events before they are handled by |
| a Logger, as they are processed by a Logger or on an Appender.</li> |
| |
| <li><b>Appender Layout:</b> Many Logback Appenders do not accept a Layout and will only send data in a |
| fixed format. Most Log4j 2 Appenders accept a Layout, allowing the data to |
| be transported in any format desired.</li> |
| |
| <li><b>Advanced Layouts:</b> Layouts in Log4j 1.x and Logback return a String. This resulted in the problems |
| discussed at <a class="externalLink" href="https://logback.qos.ch/manual/encoders.html">Logback Encoders</a>. |
| Log4j 2 takes the simpler approach that <a href="layouts.html">Layouts</a> always return a byte array. This has |
| the advantage that it means they can be used in virtually any Appender, not just |
| the ones that write to an OutputStream.</li> |
| |
| |
| <li><b>Syslog Support:</b> The <a href="appenders.html#SyslogAppender">Syslog Appender</a> supports both TCP and UDP as well as |
| support for the BSD syslog |
| and the <a class="externalLink" href="https://tools.ietf.org/html/rfc5424">RFC 5424</a> formats.</li> |
| |
| <li><b>Java Concurrency:</b> Log4j 2 takes advantage of Java 5 concurrency support and performs locking |
| at the lowest level possible. Log4j 1.x has known deadlock issues. Many of these |
| are fixed in Logback but many Logback classes still require synchronization at |
| a fairly high level.</li> |
| |
| <li><b>Community:</b> It is an Apache Software Foundation project following the community and support |
| model used by all ASF projects. If you want to contribute or gain the right to |
| commit changes just follow the path outlined at |
| <a class="externalLink" href="https://community.apache.org/contributors/">Contributing</a>.</li> |
| </ol> |
| </section> |
| </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> |