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<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="logging.html">

    &project;

  <properties>
    <title>Logging in Tomcat</title>
    <author>Allistair Crossley</author>
    <author email="yoavs@apache.org">Yoav Shapira</author>
  </properties>

<body>

<section name="Table of Contents">
<toc/>
</section>

  <section name="Introduction">
    <p>
      Logging in Apache Tomcat is implemented with the help of
      <a href="http://commons.apache.org/logging">Apache Commons Logging</a>
      library. That library is a thin wrapper above different logging
      frameworks. It provides Tomcat with the ability to log
      hierarchically across various log levels without the need to rely on a
      particular logging implementation.
    </p>

    <p>
      Since Tomcat 6.0, Tomcat uses a private package-renamed implementation of
      Apache Commons Logging, to allow web applications to use their own
      independent copies of the original Apache Commons Logging library.
      In the default distribution this private copy of the library
      is simplified and hardcoded to use the <code>java.util.logging</code> framework.
    </p>

    <p>
      To configure Tomcat to use alternative logging frameworks for its internal
      logging, one has to replace the logging library with the one that is built
      with the full implementation. Such library is provided as an <a href="extras.html">extras</a>
      component. Instructions on how to configure Tomcat to use Log4j framework
      for its internal logging may be found below.
    </p>

    <p>
      A web application running on Apache Tomcat can:
    </p>
    <ul>
      <li>
        Use system logging API, <code>java.util.logging</code>.
      </li>
      <li>
        Use logging API provided by the Java Servlets specification,
        <code>javax.servlet.ServletContext.log(...)</code>
      </li>
      <li>
        Use any logging framework of its choice.
      </li>
    </ul>

    <p>
      The logging frameworks used by different web applications run independently
      of each other. See <a href="class-loader-howto.html">class loading</a>
      for more details.
      The exception to this rule is <code>java.util.logging</code>, if it used
      directly or indirectly by your logging library. That is because it is loaded
      by the system and is shared across web applications.
    </p>

    <subsection name="Java logging API &#8212; java.util.logging">

    <p>
      Apache Tomcat has its own implementation of several key elements of
      <code>java.util.logging</code> API. This implementation is called "JULI".
      The key component there is a custom LogManager implementation,
      that is aware of different web applications running on Tomcat (and
      their different class loaders). It supports private per-application
      logging configurations. It is also notified by Tomcat when a web application
      is unloaded from memory, so that the references to its classes can be
      cleared, preventing memory leaks.
    </p>

    <p>
      This <code>java.util.logging</code> implementation is enabled by providing
      certain system properties when starting Java. The Apache Tomcat startup
      scripts do this for you, but if you are using different tools to run
      Tomcat (such as jsvc, or running Tomcat from within an IDE), you should
      take care of them by yourself.
    </p>

    <p>
      More details about java.util.logging may be found in the documentation
      for your JDK and on its Javadoc pages for the <code>java.util.logging</code>
      package.
    </p>

    <p>
      More details about Tomcat JULI may be found below.
    </p>

    </subsection>

    <subsection name="Servlets logging API">

    <p>
      The calls to <code>javax.servlet.ServletContext.log(...)</code> to write
      log messages are handled by internal Tomcat logging. Such messages are
      logged to the category named
    </p>
      <source>org.apache.catalina.core.ContainerBase.[${engine}].[${host}].[${context}]</source>
    <p>
      This logging is performed according to the Tomcat logging configuration. You
      cannot overwrite it in a web application.
    </p>

    <p>
      The Servlets logging API predates the <code>java.util.logging</code> API
      that is now provided by Java. As such, it does not offer you much options.
      E.g., you cannot control the log levels. It can be noted, though, that
      in Apache Tomcat implementation the calls to <code>ServletContext.log(String)</code>
      or <code>GenericServlet.log(String)</code> are logged at the INFO level.
      The calls to <code>ServletContext.log(String, Throwable)</code> or
      <code>GenericServlet.log(String, Throwable)</code>
      are logged at the ERROR level.
    </p>

    </subsection>

    <subsection name="Console">

    <p>
      When running Tomcat on unixes, the console output is usually redirected
      to the file named <code>catalina.out</code>. The name is configurable
      using an environment variable. (See the startup scripts).
      Whatever is written to <code>System.err/out</code> will be caught into
      that file. That may include:
    </p>

    <ul>
      <li>Uncaught exceptions printed by <code>java.lang.ThreadGroup.uncaughtException(..)</code></li>
      <li>Thread dumps, if you requested them via a system signal</li>
    </ul>

    <p>
      When running as a service on Windows, the console output is also caught
      and redirected, but the file names are different.
    </p>

    <p>
      The default logging configuration in Apache Tomcat writes the same
      messages to the console and to a log file. This is great when using
      Tomcat for development, but usually is not needed in production.
    </p>

    <p>
      Old applications that still use <code>System.out</code> or <code>System.err</code>
      can be tricked by setting <code>swallowOutput</code> attribute on a
      <a href="config/context.html">Context</a>. If the attribute is set to
      <code>true</code>, the calls to <code>System.out/err</code> during request
      processing will be intercepted, and their output will be fed to the
      logging subsystem using the
      <code>javax.servlet.ServletContext.log(...)</code> calls.<br />
      <strong>Note</strong>, that the <code>swallowOutput</code>  feature is
      actually a trick, and it has its limitations.
      It works only with direct calls to <code>System.out/err</code>,
      and only during request processing cycle. It may not work in other
      threads that might be created by the application. It cannot be used to
      intercept logging frameworks that themselves write to the system streams,
      as those start early and may obtain a direct reference to the streams
      before the redirection takes place.
    </p>

    </subsection>

    <subsection name="Access logging">

    <p>
      A related, but different feature is access logging. It can be configured
      as a valve at the Context, or Host, or Engine. See <a href="config/valve.html">Valves</a>
      documentation for more details.
    </p>

    </subsection>

  </section>

  <section name="Using java.util.logging (default)">

  <p>
    The default implementation of java.util.logging provided in the JDK is too
    limited to be useful. A limitation of JDK Logging appears to be the
    inability to have per-web application logging,  as the configuration is
    per-VM. As a result, Tomcat will, in the default configuration, replace the
    default LogManager implementation with a container friendly implementation
    called JULI, which addresses these shortcomings. It supports the same
    configuration mechanisms as the standard JDK java.util.logging, using either
    a programmatic approach, or properties files. The main difference is that
    per-classloader properties files can be set (which enables easy redeployment
    friendly webapp configuration), and the properties files support slightly
    extended constructs which allows more freedom for defining handlers and
    assigning them to loggers.
  </p>
  <p>
    JULI is enabled by default, and supports per classloader configuration, in
    addition to the regular global java.util.logging configuration. This means
    that logging can be configured at the following layers:
    <ul>
      <li>Globally. That is usually done in the
        <code>${catalina.base}/conf/logging.properties</code> file.
        The file is specified by the <code>java.util.logging.config.file</code>
        System property which is set by the startup scripts.
        If it is not readable or is not configured, the default is to use the
        <code>${java.home}/lib/logging.properties</code> file in the JRE.
      </li>
      <li>In the web application. The file will be
        <code>WEB-INF/classes/logging.properties</code>
      </li>
    </ul>
  </p>
  <p>
    The default <code>logging.properties</code> in the JRE specifies a
    <code>ConsoleHandler</code> that routes logging to System.err.
    The default <code>conf/logging.properties</code> in Apache Tomcat also
    adds several <code>FileHandler</code>s that write to files.
  </p>
  <p>
    A handler's log level threshold is INFO by default and can be set using
    SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST or ALL.
    You can also target specific packages to collect logging from and specify
    a level.
  </p>
  <p>
    Here is how you would set debugging from Tomcat. You would need to ensure the
    ConsoleHandler's (or FileHandler's') level is also set to collect this threshold,
    so FINEST or ALL should be set. Please refer to <code>java.util.logging</code>
    documentation in the JDK for the complete details:
  </p>
  <p>
    <source>org.apache.catalina.level=FINEST</source>
  </p>
  <p>
    The configuration used by JULI is extremely similar to the one supported by
    plain <code>java.util.logging</code>, but uses a few
    extensions to allow better flexibility in assigning loggers. The main
    differences are:
  </p>
  <ul>
      <li>A prefix may be added to handler names, so that multiple handlers of a
      single class may be instantiated. A prefix is a String which starts with a
      digit, and ends with '.'. For example, <code>22foobar.</code> is a valid
      prefix.</li>
      <li>System property replacement is performed for property values which
      contain ${systemPropertyName}.</li>
      <li>As in Java 6.0, loggers can define a list of handlers using the
      <code>loggerName.handlers</code> property.</li>
      <li>By default, loggers will not delegate to their parent if they have
      associated handlers. This may be changed per logger using the
      <code>loggerName.useParentHandlers</code> property, which accepts a
      boolean value.</li>
      <li>The root logger can define its set of handlers using the
      <code>.handlers</code> property.</li>
  </ul>
  <p>
    There are several additional implementation classes, that can be used
    together with the ones provided by Java. The notable one is
    <code>org.apache.juli.FileHandler</code>.
  </p>
  <p>
    <code>org.apache.juli.FileHandler</code> supports buffering of the
      logs. The buffering is not enabled by default. To configure it, use the
      <code>bufferSize</code> property of a handler. A value of <code>0</code>
      uses system default buffering (typically an 8K buffer will be used). A
      value of <code>&lt;0</code> forces a writer flush upon each log write. A
      value <code>&gt;0</code> uses a BufferedOutputStream with the defined
      value but note that the system default buffering will also be
      applied.
  </p>
  <p>
    Example logging.properties file to be placed in $CATALINA_BASE/conf:
    <source>
handlers = 1catalina.org.apache.juli.FileHandler, \
           2localhost.org.apache.juli.FileHandler, \
           3manager.org.apache.juli.FileHandler, \
           java.util.logging.ConsoleHandler

.handlers = 1catalina.org.apache.juli.FileHandler, java.util.logging.ConsoleHandler

############################################################
# Handler specific properties.
# Describes specific configuration info for Handlers.
############################################################

1catalina.org.apache.juli.FileHandler.level = FINE
1catalina.org.apache.juli.FileHandler.directory = ${catalina.base}/logs
1catalina.org.apache.juli.FileHandler.prefix = catalina.

2localhost.org.apache.juli.FileHandler.level = FINE
2localhost.org.apache.juli.FileHandler.directory = ${catalina.base}/logs
2localhost.org.apache.juli.FileHandler.prefix = localhost.

3manager.org.apache.juli.FileHandler.level = FINE
3manager.org.apache.juli.FileHandler.directory = ${catalina.base}/logs
3manager.org.apache.juli.FileHandler.prefix = manager.
3manager.org.apache.juli.FileHandler.bufferSize = 16384

java.util.logging.ConsoleHandler.level = FINE
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter


############################################################
# Facility specific properties.
# Provides extra control for each logger.
############################################################

org.apache.catalina.core.ContainerBase.[Catalina].[localhost].level = INFO
org.apache.catalina.core.ContainerBase.[Catalina].[localhost].handlers = \
   2localhost.org.apache.juli.FileHandler

org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager].level = INFO
org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager].handlers = \
   3manager.org.apache.juli.FileHandler

# For example, to log debug messages in ContextConfig and HostConfig
# classes and to log only warnings and errors in other
# org.apache.catalina.** classes, uncomment these lines:
#org.apache.catalina.startup.ContextConfig.level = FINE
#org.apache.catalina.startup.HostConfig.level = FINE
#org.apache.catalina.level = WARNING
</source>
    </p>
    
    <p>
      Example logging.properties for the servlet-examples web application to be
      placed in WEB-INF/classes inside the web application:
      <source>
handlers = org.apache.juli.FileHandler, java.util.logging.ConsoleHandler

############################################################
# Handler specific properties.
# Describes specific configuration info for Handlers.
############################################################

org.apache.juli.FileHandler.level = FINE
org.apache.juli.FileHandler.directory = ${catalina.base}/logs
org.apache.juli.FileHandler.prefix = servlet-examples.

java.util.logging.ConsoleHandler.level = FINE
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
</source>
    </p>

    <subsection name="Documentation references">
      <p>See the following resources for additional information:</p>
      <ul>
        <li>Apache Tomcat Javadoc for the
          <a href="api/org/apache/juli/package-summary.html"><code>org.apache.juli</code></a>
          package.
        </li>
        <li>Oracle Java 6 Javadoc for the
          <a href="http://docs.oracle.com/javase/6/docs/api/java/util/logging/package-summary.html"><code>java.util.logging</code></a>
          package.
        </li>
      </ul>
    </subsection>

    <subsection name="Considerations for productive usage">
      <p>You may want to take note of the following:</p>
      <ul>
        <li><p>Consider removing <code>ConsoleHandler</code> from configuration.</p>
        <p>By default (thanks to the <code>.handlers</code> setting) logging goes
        both to a <code>FileHandler</code> and to a <code>ConsoleHandler</code>.
        The output of the latter one is usually captured into a file, such as
        <code>catalina.out</code>. Thus you end up with two copies of the same
        messages.</p>
        </li>
        <li><p>Consider removing <code>FileHandler</code>s for the applications
        that you do not use. E.g., the one for <code>host-manager</code>.</p></li>
        <li><p>The handlers by default use the system default encoding to write
        the log files. It can be configured with <code>encoding</code> property.
        See Javadoc for details.</p></li>
        <li><p>Consider configuring an <a href="config/valve.html">Access
        log</a>.</p></li>
      </ul>
    </subsection>

  </section>

  <section name="Using Log4j">
    <p>
      This section explains how to configure Tomcat to use
      <a href="http://logging.apache.org/log4j/">log4j</a> rather than
      java.util.logging for all Tomcat's internal logging.
    </p>
    <p><em>Note</em>: The steps described in this section are needed
      when you want to reconfigure Tomcat to use Apache log4j for its own
      logging. These steps are <strong>not</strong> needed if you just want
      to use log4j in your own web application. &#8212; In that case, just
      put <code>log4j.jar</code> and <code>log4j.properties</code> into
      <code>WEB-INF/lib</code> and <code>WEB-INF/classes</code>
      of your web application.
    </p>
    <p>
      The following steps describe configuring log4j to output Tomcat's
      internal logging.
    </p>

    <ol>
        <li>Create a file called <code>log4j.properties</code> with the 
        following content and save it into <code>$CATALINA_BASE/lib</code></li>
    </ol>
    <source>
log4j.rootLogger=INFO, CATALINA

# Define all the appenders
log4j.appender.CATALINA=org.apache.log4j.DailyRollingFileAppender
log4j.appender.CATALINA.File=${catalina.base}/logs/catalina.
log4j.appender.CATALINA.Append=true
log4j.appender.CATALINA.Encoding=UTF-8
# Roll-over the log once per day
log4j.appender.CATALINA.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.CATALINA.layout = org.apache.log4j.PatternLayout
log4j.appender.CATALINA.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

log4j.appender.LOCALHOST=org.apache.log4j.DailyRollingFileAppender
log4j.appender.LOCALHOST.File=${catalina.base}/logs/localhost.
log4j.appender.LOCALHOST.Append=true
log4j.appender.LOCALHOST.Encoding=UTF-8
log4j.appender.LOCALHOST.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.LOCALHOST.layout = org.apache.log4j.PatternLayout
log4j.appender.LOCALHOST.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

log4j.appender.MANAGER=org.apache.log4j.DailyRollingFileAppender
log4j.appender.MANAGER.File=${catalina.base}/logs/manager.
log4j.appender.MANAGER.Append=true
log4j.appender.MANAGER.Encoding=UTF-8
log4j.appender.MANAGER.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.MANAGER.layout = org.apache.log4j.PatternLayout
log4j.appender.MANAGER.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

log4j.appender.HOST-MANAGER=org.apache.log4j.DailyRollingFileAppender
log4j.appender.HOST-MANAGER.File=${catalina.base}/logs/host-manager.
log4j.appender.HOST-MANAGER.Append=true
log4j.appender.HOST-MANAGER.Encoding=UTF-8
log4j.appender.HOST-MANAGER.DatePattern='.'yyyy-MM-dd'.log'
log4j.appender.HOST-MANAGER.layout = org.apache.log4j.PatternLayout
log4j.appender.HOST-MANAGER.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.Encoding=UTF-8
log4j.appender.CONSOLE.layout = org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern = %d [%t] %-5p %c- %m%n

# Configure which loggers log to which appenders
log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost]=INFO, LOCALHOST
log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager]=\
  INFO, MANAGER
log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/host-manager]=\
  INFO, HOST-MANAGER
</source>
    <ol start="2">
        <li><a href="http://logging.apache.org/log4j">Download Log4J</a> 
        (v1.2 or later).</li>

        <li><p>Download or build <code>tomcat-juli.jar</code> and
        <code>tomcat-juli-adapters.jar</code> that are available as an "extras"
        component for Tomcat. See <a href="extras.html">Additional Components
        documentation</a> for details.</p>
        <p>This <code>tomcat-juli.jar</code> differs from the default one. It
        contains the full Apache Commons Logging implementation and thus is
        able to discover the presense of log4j and configure itself.</p>
        </li>

        <li><p>If you want to configure Tomcat to use log4j globally:</p>
        <ul>
          <li>Put <code>log4j.jar</code> and
            <code>tomcat-juli-adapters.jar</code> from "extras" into
            <code>$CATALINA_HOME/lib</code>.</li>
          <li>Replace <code>$CATALINA_HOME/bin/tomcat-juli.jar</code> with
          <code>tomcat-juli.jar</code> from "extras".</li>
        </ul>
        </li>

        <li><p>If you are running Tomcat with separate $CATALINA_HOME and
        $CATALINA_BASE and want to configure to use log4j in a single
        $CATALINA_BASE only:</p>
        <ul>
          <li>Create <code>$CATALINA_BASE/bin</code> and
          <code>$CATALINA_BASE/lib</code> directories if they do not exist.
          </li>
          <li>Put <code>log4j.jar</code> and
             <code>tomcat-juli-adapters.jar</code> from "extras" into
             <code>$CATALINA_BASE/lib</code></li>
          <li>Put <code>tomcat-juli.jar</code> from "extras" as
          <code>$CATALINA_BASE/bin/tomcat-juli.jar</code></li>
          <li>If you are running with a
          <a href="security-manager-howto.html">security manager</a>, you
          would need to edit the
          <code>$CATALINA_BASE/conf/catalina.policy</code> file to adjust
          it to using a different copy of tomcat-juli.jar.</li>
          <li>The old <code>tomcat-juli.jar</code> in
          <code>$CATALINA_HOME/bin</code> is still referenced by manifest of
          <code>bootstrap.jar</code> and thus will be implicitly present
          on Tomcat's classpath. The startup scripts configure
          <code>$CATALINA_BASE/bin/tomcat-juli.jar</code> to be earlier on the
          classpath than <code>bootstrap.jar</code>, and so it should have
          higher priority. Thus it should be OK, but
          consider removing the unneeded copy of <code>tomcat-juli.jar</code>
          (copy it into all other $CATALINA_BASEs that do not use log4j).
          Tomcat 7 does not have this issue.</li>
        </ul>
        </li>

        <li><p>Delete <code>$CATALINA_BASE/conf/logging.properties</code> to
        prevent java.util.logging generating zero length log files.</p></li>

        <li><p>Start Tomcat</p></li>
    </ol>

    <p>
      This log4j configuration mirrors the default java.util.logging setup
      that ships with Tomcat: both the manager and host-manager apps get an
      individual log file, and everything else goes to the "catalina.log" log
      file. Each file is rolled-over once per day.
    </p>

    <p>
      You can (and should) be more picky about which packages to include 
      in the logging. Tomcat defines loggers by Engine and Host names.
      For example, for a more detailed Catalina localhost log, add this to the
      end of the log4j.properties above. Note that there are known issues with 
      using this naming convention (with square brackets) in log4j XML based
      configuration files, so we recommend you use a properties file as
      described until a future version of log4j allows this convention.
    </p>
      <source>
log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost]=DEBUG<br />
log4j.logger.org.apache.catalina.core=DEBUG<br />
log4j.logger.org.apache.catalina.session=DEBUG<br />
</source>

    <p>
      Be warned: a level of DEBUG will produce megabytes of logging and slow
      startup of Tomcat. This level should be used sparingly when debugging of
      internal Tomcat operations is required.
    </p>

    <p>
      Your web applications should certainly use their own log4j configuration. 
      This is valid <i>with</i> the above configuration.  You would place a
      similar log4j.properties file in your web application's WEB-INF/classes
      directory, and log4jx.y.z.jar into WEB-INF/lib. Then specify your package
      level logging. This is a basic setup of log4j which does *not* require
      Commons-Logging, and you should consult the 
      <a href="http://logging.apache.org/log4j/docs/documentation.html">log4j
      documentation</a> for more options. This page is intended only as a
      bootstrapping guide.
    </p>

    <p><em>Additional notes</em></p>
    <ul>
        <li><p>This exposes log4j libraries to the web applications through the
        Common classloader. See <a href="class-loader-howto.html">class loading</a>
        documentation for details.</p>
        <p>Because of that, the web applications and libraries using
        <a href="http://commons.apache.org/logging">Apache Commons Logging</a>
        library are likely to automatically choose log4j as the underlying
        logging implementation.</p></li>

        <li><p>The <code>java.util.logging</code> API is still available, for
        those web applications that use it directly. The
        <code>${catalina.base}/conf/logging.properties</code> file is still
        referenced by Tomcat startup scripts.</p>
        <p> Removal of <code>${catalina.base}/conf/logging.properties</code>
        file, mentioned as one of the steps, just causes
        <code>java.util.logging</code> to fallback to the default configuration
        as configured in JRE, which is to use a ConsoleHandler and do not
        create any files.</p></li>
    </ul>
  </section>

</body>
</document>
