webapps/docs/config/listeners.xml

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

  &project;

  <properties>
    <title>The LifeCycle Listener Component</title>
  </properties>

<body>

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

<section name="Introduction">

  <p>A <strong>Listener</strong> element defines a component that performs
  actions when specific events occur, usually Tomcat starting or Tomcat
  stopping.</p>

  <p>Listeners may be nested inside a <a href="server.html">Server</a>,
  <a href="engine.html">Engine</a>, <a href="host.html">Host</a> or
  <a href="context.html">Context</a>. Some Listeners are only intended to be
  nested inside specific elements. These constraints are noted in the
  documentation below.</p>

</section>

<section name="Attributes">

  <subsection name="Common Attributes">

    <p>All implementations of <strong>Listener</strong>
    support the following attributes:</p>

    <attributes>

      <attribute name="className" required="true">
        <p>Java class name of the implementation to use. This class must
        implement the <code>org.apache.catalina.LifecycleListener</code>
        interface.</p>
      </attribute>

    </attributes>

  </subsection>

</section>

<section name="Nested Components">

  <p>No element may be nested inside a <strong>Listener</strong>.</p>

</section>

<section name="Standard Implementations">

  <p>Unlike most Catalina components, there are several standard
  <strong>Listener</strong> implementations available.  As a result,
  the <code>className</code> attribute MUST be used to select the
  implementation you wish to use.</p>

  <subsection name="APR Lifecycle Listener - org.apache.catalina.core.AprLifecycleListener">

    <p>The <strong>APR Lifecycle Listener</strong> checks for the presence of
    the APR/native library and loads the library if it is present. For more
    information see the <a href="../apr.html">APR/native guide</a>.</p>

    <p>This listener must only be nested within <a href="server.html">Server</a>
    elements.</p>

    <p>The following additional attributes are supported by the <strong>APR
    Lifecycle Listener</strong>:</p>

    <attributes>

      <attribute name="SSLEngine" required="false">
        <p>Name of the SSLEngine to use. <code>off</code>: do not use SSL,
        <code>on</code>: use SSL but no specific ENGINE.</p>
        <p>The default value is <b>on</b>. This initializes the
        native SSL engine, which must be enabled in the APR/native connector by
        the use of the <code>SSLEnabled</code> attribute.</p>
        <p>See the <a href="http://www.openssl.org/">Official OpenSSL website</a>
        for more details on supported SSL hardware engines and manufacturers.
        </p>
        <p>Tomcat Native 2.x onwards requires SSL so if SSLEngine is set to
        <code>off</code> when using Tomcat Native 2.x onwards, the APR/native
        library will be disabled.</p>
      </attribute>

      <attribute name="SSLRandomSeed" required="false">
        <p>Entropy source used to seed the SSLEngine's PRNG. The default value
        is <code>builtin</code>. On development systems, you may want to set
        this to <code>/dev/urandom</code> to allow quicker start times.</p>
      </attribute>

      <attribute name="FIPSMode" required="false">
        <p>The behaviour of this attribute depends on whether Tomcat Native has
        been compiled against OpenSSL 1.x or OpenSSL 3.x.</p>
        <p>For OpenSSL 1.x: Set to <code>on</code> to request that OpenSSL be in
        FIPS mode (if OpenSSL is already in FIPS mode, it will remain in FIPS
        mode).
        Set to <code>enter</code> to force OpenSSL to enter FIPS mode (an
        error will occur if OpenSSL is already in FIPS mode).
        Set to <code>require</code> to require that OpenSSL <i>already</i> be
        in FIPS mode (an error will occur if OpenSSL is not already in FIPS
        mode).</p>
        <p>For OpenSSL 3.x: <code>on</code>, <code>enter</code> and
        <code>require</code> all behave the same way. If the FIPS provider is
        the default provider, it will be used. If the FIPS provider is not the
        default provider, an error will occur.</p>
        <p>FIPS mode <em>requires you to have a FIPS-capable OpenSSL library</em>.
        If this attribute is set to anything other than <code>off</code>, the
        <b>SSLEngine</b> must be enabled as well.</p>
        <p>The default value is <code>off</code>.</p>
      </attribute>

      <attribute name="useOpenSSL" required="false">
        <p>This attribute controls the auto-selection of the OpenSSL JSSE
        implementation. The default is <code>true</code> which will use OpenSSL
        if the native library is available and a NIO or NIO2 connector is used.</p>
      </attribute>

    </attributes>

  </subsection>

  <subsection name="Global Resources Lifecycle Listener - org.apache.catalina.mbeans.GlobalResourcesLifecycleListener">

    <p>The <strong>Global Resources Lifecycle Listener</strong> initializes the
    Global JNDI resources defined in server.xml as part of the <a
    href="globalresources.html">Global Resources</a> element. Without this
    listener, none of the Global Resources will be available.</p>

    <p>This listener must only be nested within <a href="server.html">Server</a>
    elements.</p>

    <p>No additional attributes are supported by the <strong>Global Resources
    Lifecycle Listener</strong>.</p>

  </subsection>

  <subsection name="JNI Library Loading Listener - org.apache.catalina.core.JniLifecycleListener">

    <p>The <strong>JNI Library Loading Listener</strong> makes it possible
    for multiple Webapps to use a native library, by loading the native
    library using a shared class loader (typically the Common class loader but
    may vary in some configurations)</p>

    <p>The listener supports two mutually exclusive attributes, so one of them must be used, but you can not use both together:</p>

    <attributes>
      <attribute name="libraryName" required="false">
        <p>The name of the native library, as defined in
        <code>java.lang.System.loadLibrary()</code>
        </p>
      </attribute>
      <attribute name="libraryPath" required="false">
        <p>The absolute path of the native library, as defined in
        <code>java.lang.System.load()</code>
        </p>
      </attribute>
    </attributes>
  </subsection>

  <subsection name="JRE Memory Leak Prevention Listener - org.apache.catalina.core.JreMemoryLeakPreventionListener">

    <p>The <strong>JRE Memory Leak Prevention Listener</strong> provides
    work-arounds for known places where the Java Runtime environment uses
    the context class loader to load a singleton as this will cause a memory
    leak if a web application class loader happens to be the context class
    loader at the time. The work-around is to initialise these singletons when
    this listener starts as Tomcat's common class loader is the context class
    loader at that time. It also provides work-arounds for known issues that
    can result in locked JAR files.</p>

    <p>This listener must only be nested within <a href="server.html">Server</a>
    elements.</p>

    <p>The following additional attributes are supported by the <strong>JRE
    Memory Leak Prevention Listener</strong>:</p>

    <attributes>

      <attribute name="appContextProtection" required="false">
        <p>Enables protection so that calls to
        <code>sun.awt.AppContext.getAppContext()</code> triggered by a web
        application do not result in a memory leak. Note that enabling this
        protection will trigger a requirement for a graphical environment unless
        Java is started in head-less mode. The default is <code>false</code>.
        </p>
      </attribute>

      <attribute name="classesToInitialize" required="false">
        <p>List of comma-separated fully qualified class names to load and initialize
        during the startup of this Listener. This allows to pre-load classes that are
        known to provoke classloader leaks if they are loaded during a request
        processing. Non-JRE classes may be referenced, like
        <code>oracle.jdbc.driver.OracleTimeoutThreadPerVM</code>.
        The default value is empty, but specific JRE classes are loaded by other leak
        protection features managed by other attributes of this Listener.</p>
      </attribute>

      <attribute name="driverManagerProtection" required="false">
        <p>The first use of <code>java.sql.DriverManager</code> will trigger the
        loading of JDBC Drivers visible to the current class loader and its
        parents. The web application level memory leak protection can take care
        of this in most cases but triggering the loading here has fewer
        side-effects. The default is <code>true</code>.</p>
      </attribute>

      <attribute name="initSeedGenerator" required="false">
        <p>The first use of <code>SeedGenerator</code>, an internal class of
        the default security spi implementation, might create a thread on some
        platforms. Depending on the timing of the first use of a secure random
        this thread might become associated with a webapp classloader, causing
        a memory leak. Setting this to <code>true</code> will initialize the
        seed. The default is <code>false</code> to avoid consuming random if
        not needed.</p>
      </attribute>

      <attribute name="urlCacheProtection" required="false">
        <p>Enables protection so that reading resources from JAR files using
        <code>java.net.URLConnection</code>s does not result in the JAR file
        being locked. Note that enabling this protection disables caching by
        default for all resources obtained via
        <code>java.net.URLConnection</code>s. Caching may be re-enabled on a
        case by case basis as required. Defaults to <code>true</code>.</p>
      </attribute>

    </attributes>

    <subsection name="JreMemoryLeakPreventionListener Examples">

      <p>The following is an example of how to configure the
      <code>classesToInitialize</code> attribute of this listener.</p>

      <p>If this listener was configured in server.xml as:</p>

      <source><![CDATA[  <Listener className="org.apache.catalina.core.JreMemoryLeakPreventionListener"
            classesToInitialize="oracle.jdbc.driver.OracleTimeoutThreadPerVM" />]]></source>

      <p>then the <code>OracleTimeoutThreadPerVM</code> class would be loaded
      and initialized during listener startup instead of during request
      processing.</p>

    </subsection>

  </subsection>

  <subsection name="Security Lifecycle Listener - org.apache.catalina.security.SecurityListener">

    <p>The <strong>Security Lifecycle Listener</strong> performs a number of
    security checks when Tomcat starts and prevents Tomcat from starting if they
    fail. The listener is not enabled by default. To enabled it uncomment the
    listener in $CATALINA_BASE/conf/server.xml.</p>

    <p>This listener must only be nested within <a href="server.html">Server</a>
    elements.</p>

    <p>The following additional attributes are supported by the <strong>Security
    Lifecycle Listener</strong>:</p>

    <attributes>

      <attribute name="checkedOsUsers" required="false">
        <p>A comma separated list of OS users that must not be used to start
        Tomcat. If not specified, the default value of <b>root</b> is used. To
        disable this check, set the attribute to the empty string. Usernames
        are checked in a case-insensitive manner.</p>
      </attribute>

      <attribute name="minimumUmask" required="false">
        <p>The least restrictive umask that must be configured before Tomcat
        will start. If not specified, the default value of <b>0007</b> is used.
        To disable this check, set the attribute to the empty string. The check
        is not performed on Windows platforms.</p>
      </attribute>

    </attributes>

  </subsection>

  <subsection name="StoreConfig Lifecycle Listener - org.apache.catalina.storeconfig.StoreConfigLifecycleListener">

    <p>The <strong>StoreConfig Lifecycle Listener</strong> configures a
    StoreConfig MBean that may be used to save the current server configuration
    in server.xml or the current configuration for a web application in a
    context.xml file.</p>

    <p>This listener must only be nested within <a href="server.html">Server</a>
    elements.</p>

    <p>The following additional attributes are supported by the
    <strong>StoreConfig Lifecycle Listener</strong>:</p>

    <attributes>

      <attribute name="storeConfigClass" required="false">
        <p>The name of the <code>IStoreConfig</code> implementation to use. If
        not specified the default of
        <code>org.apache.catalina.storeconfig.StoreConfig</code> will be
        used.</p>
      </attribute>

      <attribute name="storeRegistry" required="false">
        <p>The URL of the configuration file that configures how the
        <code>IStoreConfig</code> is to save the configuration. If not specified
        the built in resource
        <code>/org/apache/catalina/storeconfig/server-registry.xml</code> will
        be used.</p>
      </attribute>

    </attributes>

  </subsection>

  <subsection name="ThreadLocal Leak Prevention Listener - org.apache.catalina.core.ThreadLocalLeakPreventionListener">

    <p>The <strong>ThreadLocal Leak Prevention Listener</strong> triggers the
    renewal of threads in <a href="executor.html">Executor</a> pools when a
    <a href="context.html">Context</a> is being stopped to avoid thread-local
    related memory leaks. Active threads will be renewed one by one when they
    come back to the pool after executing their task. The renewal happens
    only for contexts that have their <code>renewThreadsWhenStoppingContext</code>
    attribute set to <code>true</code>.</p>

    <p>This listener must only be nested within <a href="server.html">Server</a>
    elements.</p>

    <p>No additional attributes are supported by the <strong>ThreadLocal Leak
    Prevention Listener</strong>.</p>

  </subsection>

  <subsection name="UserConfig - org.apache.catalina.startup.UserConfig">

    <p>The <strong>UserConfig</strong> provides feature of User Web Applications.
    User Web Applications map a request URI starting with a tilde character ("~")
    and a username to a directory (commonly named public_html) in that user's
    home directory on the server.</p>

    <p>See the <a href="host.html#User_Web_Applications">User Web Applications</a>
    special feature on the <strong>Host</strong> element for more information.</p>

    <p>The following additional attributes are supported by the
    <strong>UserConfig</strong>:</p>

    <attributes>

      <attribute name="directoryName" required="false">
        <p>The directory name to be searched for within each user home directory.
        The default is <code>public_html</code>.</p>
      </attribute>

      <attribute name="userClass" required="false">
        <p>The class name of the user database class.
        There are currently two user database, the
        <code>org.apache.catalina.startup.PasswdUserDatabase</code> is used on a
        Unix system that uses the /etc/passwd file to identify valid users.
        The <code>org.apache.catalina.startup.HomesUserDatabase</code> is used on
        a server where /etc/passwd is not in use. HomesUserDatabase deploy all
        directories found in a specified base directory.</p>
      </attribute>

      <attribute name="homeBase" required="false">
        <p>The base directory containing user home directories. This is effective
        only when <code>org.apache.catalina.startup.HomesUserDatabase</code> is
        used.</p>
      </attribute>

      <attribute name="allow" required="false">
        <p>A regular expression defining user who deployment is allowed. If this
        attribute is specified, the user to deploy must match for this pattern.
        If this attribute is not specified, all users will be deployed unless the
        user matches a deny pattern.</p>
      </attribute>

      <attribute name="deny" required="false">
        <p>A regular expression defining user who deployment is denied. If this
        attribute is specified, the user to deploy must not match for this
        pattern. If this attribute is not specified, deployment of user will be
        governed by a allow attribute.</p>
      </attribute>

    </attributes>

  </subsection>

  <subsection name="Version Logging Lifecycle Listener - org.apache.catalina.startup.VersionLoggerListener">

    <p>The <strong>Version Logging Lifecycle Listener</strong> logs Tomcat, Java
    and operating system information when Tomcat starts.</p>

    <p>This listener must only be nested within <a href="server.html">Server</a>
    elements and should be the first listener defined.</p>

    <p>The following additional attributes are supported by the <strong>Version
    Logging Lifecycle Listener</strong>:</p>

    <attributes>

      <attribute name="logArgs" required="false">
        <p>If <code>true</code>, the command line arguments passed to Java when
        Tomcat started will be logged. If not specified, the default value of
        <code>true</code> will be used.</p>
      </attribute>

      <attribute name="logEnv" required="false">
        <p>If <code>true</code>, the current environment variables when Tomcat
        starts will be logged. If not specified, the default value of
        <code>false</code> will be used.</p>
      </attribute>

      <attribute name="logProps" required="false">
        <p>If <code>true</code>, the current Java system properties will be
        logged. If not specified, the default value of
        <code>false</code> will be used.</p>
      </attribute>

    </attributes>

  </subsection>

  <subsection name="HTTPD mod_heartmonitor Listener - org.apache.catalina.ha.backend.HeartbeatListener">

    <p>The <strong>HTTPD mod_heartmonitor Listener</strong> allows tomcat to send heart beat message to
    the Apache HTTPD mod_heartmonitor module.</p>

    <p>The following additional attributes are supported by the <strong>HTTPD mod_heartmonitor
    Listener</strong>:</p>

    <attributes>
      <attribute name="Port" required="false">
        <p>Port the connector that will received proxied traffic from HTTPD, default the first connector will be used</p>
      </attribute>

      <attribute name="Host" required="false">
        <p>Host it is the IP corresponding the <strong>address</strong> of the connector that will received proxied traffic,
        default empty the <strong>Port</strong> will be used</p>
      </attribute>

      <attribute name="proxyURL" required="false">
        <p>proxyURL is the URL corresponding to the <strong>Location</strong> in httpd configuration of the heartbeat Handler,
        default /HeartbeatListener</p>
      </attribute>

      <attribute name="ProxyList" required="false">
        <p>ProxyList is the list of proxies from which tomcat is going to receive requests,
        formatted like "address:port,address:port" once filled the multicast logic is disable and the multi parameters are
        ignored</p>
      </attribute>

      <attribute name="Group" required="false">
        <p>Group is the Multicast IP to broadcast messages to HTTPD, default 224.0.1.105</p>
      </attribute>

      <attribute name="Multiport" required="false">
        <p>Multiport is the Multicast port to broadcast messages to HTTPD, default 23364</p>
      </attribute>

      <attribute name="Ttl" required="false">
        <p>Ttl is the TTL for the broadcast messages, default 16</p>
      </attribute>

    </attributes>
  </subsection>
</section>

</body>

</document>