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161 lines
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<html lang="en"><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><link href="../images/docs-stylesheet.css" rel="stylesheet" type="text/css"><title>Apache Tomcat 8 Configuration Reference (8.0.53) - The Loader Component</title><meta name="author" content="Craig R. McClanahan"><script type="application/javascript" data-comments-identifier="tomcat-8.0-doc/config/loader">
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</script></head><body><div id="wrapper"><header><div id="header"><div><div><div class="logo noPrint"><a href="https://tomcat.apache.org/"><img alt="Tomcat Home" src="../images/tomcat.png"></a></div><div style="height: 1px;"></div><div class="asfLogo noPrint"><a href="https://www.apache.org/" target="_blank"><img src="../images/asf-logo.svg" alt="The Apache Software Foundation" style="width: 266px; height: 83px;"></a></div><h1>Apache Tomcat 8 Configuration Reference</h1><div class="versionInfo">
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Version 8.0.53,
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<time datetime="2018-06-29">Jun 29 2018</time></div><div style="height: 1px;"></div><div style="clear: left;"></div></div></div></div></header><div id="middle"><div><div id="mainLeft" class="noprint"><div><nav><div><h2>Links</h2><ul><li><a href="../index.html">Docs Home</a></li><li><a href="index.html">Config Ref. Home</a></li><li><a href="https://wiki.apache.org/tomcat/FAQ">FAQ</a></li><li><a href="#comments_section">User Comments</a></li></ul></div><div><h2>Top Level Elements</h2><ul><li><a href="server.html">Server</a></li><li><a href="service.html">Service</a></li></ul></div><div><h2>Executors</h2><ul><li><a href="executor.html">Executor</a></li></ul></div><div><h2>Connectors</h2><ul><li><a href="http.html">HTTP</a></li><li><a href="ajp.html">AJP</a></li></ul></div><div><h2>Containers</h2><ul><li><a href="context.html">Context</a></li><li><a href="engine.html">Engine</a></li><li><a href="host.html">Host</a></li><li><a href="cluster.html">Cluster</a></li></ul></div><div><h2>Nested Components</h2><ul><li><a href="cookie-processor.html">CookieProcessor</a></li><li><a href="credentialhandler.html">CredentialHandler</a></li><li><a href="globalresources.html">Global Resources</a></li><li><a href="jar-scanner.html">JarScanner</a></li><li><a href="jar-scan-filter.html">JarScanFilter</a></li><li><a href="listeners.html">Listeners</a></li><li><a href="loader.html">Loader</a></li><li><a href="manager.html">Manager</a></li><li><a href="realm.html">Realm</a></li><li><a href="resources.html">Resources</a></li><li><a href="sessionidgenerator.html">SessionIdGenerator</a></li><li><a href="valve.html">Valve</a></li></ul></div><div><h2>Cluster Elements</h2><ul><li><a href="cluster.html">Cluster</a></li><li><a href="cluster-manager.html">Manager</a></li><li><a href="cluster-channel.html">Channel</a></li><li><a href="cluster-membership.html">Channel/Membership</a></li><li><a href="cluster-sender.html">Channel/Sender</a></li><li><a href="cluster-receiver.html">Channel/Receiver</a></li><li><a href="cluster-interceptor.html">Channel/Interceptor</a></li><li><a href="cluster-valve.html">Valve</a></li><li><a href="cluster-deployer.html">Deployer</a></li><li><a href="cluster-listener.html">ClusterListener</a></li></ul></div><div><h2>web.xml</h2><ul><li><a href="filter.html">Filter</a></li></ul></div><div><h2>Other</h2><ul><li><a href="systemprops.html">System properties</a></li></ul></div></nav></div></div><div id="mainRight"><div id="content"><h2>The Loader Component</h2><h3 id="Table_of_Contents">Table of Contents</h3><div class="text">
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<ul><li><a href="#Introduction">Introduction</a></li><li><a href="#Attributes">Attributes</a><ol><li><a href="#Common_Attributes">Common Attributes</a></li><li><a href="#Standard_Implementation">Standard Implementation</a></li></ol></li><li><a href="#Nested_Components">Nested Components</a></li><li><a href="#Special_Features">Special Features</a><ol><li><a href="#Logging">Logging</a></li></ol></li></ul>
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</div><h3 id="Introduction">Introduction</h3><div class="text">
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<p>The <strong>Loader</strong> element represents the <em>web
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application class loader</em> that will be used to load Java
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classes and resources for your web application. Such
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a class loader must follow the requirements of the Servlet
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Specification, and load classes from the following locations:</p>
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<ul>
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<li>From the <code>/WEB-INF/classes</code> directory inside your
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web application.</li>
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<li>From JAR files in the <code>/WEB-INF/lib</code> directory
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inside your web application.</li>
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<li>From resources made available by Catalina to all web
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applications globally.</li>
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</ul>
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<p>A Loader element MAY be nested inside a <a href="context.html">Context</a>
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component. If it is not included, a default Loader configuration will be
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created automatically, which is sufficient for most requirements.</p>
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<p>For a more in-depth description of the class loader hierarchy
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that is implemented by Catalina, see <a href="../class-loader-howto.html">the ClassLoader HowTo</a>.</p>
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<p><em>The description below uses the variable name $CATALINA_BASE to refer the
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base directory against which most relative paths are resolved. If you have
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not configured Tomcat for multiple instances by setting a CATALINA_BASE
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directory, then $CATALINA_BASE will be set to the value of $CATALINA_HOME,
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the directory into which you have installed Tomcat.</em></p>
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</div><h3 id="Attributes">Attributes</h3><div class="text">
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<div class="subsection"><h4 id="Common_Attributes">Common Attributes</h4><div class="text">
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<p>All implementations of <strong>Loader</strong>
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support the following attributes:</p>
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<table class="defaultTable"><tr><th style="width: 15%;">
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Attribute
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</th><th style="width: 85%;">
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Description
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</th></tr><tr><td><code class="attributeName">className</code></td><td>
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<p>Java class name of the implementation to use. This class must
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implement the <code>org.apache.catalina.Loader</code> interface.
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If not specified, the standard value (defined below) will be used.</p>
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</td></tr><tr><td><code class="attributeName">delegate</code></td><td>
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<p>Set to <code>true</code> if you want the class loader to follow
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the standard Java2 delegation model, and attempt to load classes from
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parent class loaders <strong>before</strong> looking inside the web
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application. Set to <code>false</code> (the default) to have the
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class loader look inside the web application first, before asking
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parent class loaders to find requested classes or resources.</p>
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</td></tr><tr><td><code class="attributeName">reloadable</code></td><td>
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<p>Set to <code>true</code> if you want Catalina to monitor classes in
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<code>/WEB-INF/classes/</code> and <code>/WEB-INF/lib</code> for
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changes, and automatically reload the web application if a change
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is detected. This feature is very useful during application
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development, but it requires significant runtime overhead and is
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not recommended for use on deployed production applications. You
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can use the <a href="../manager-howto.html">Manager</a> web
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application, however, to trigger reloads of deployed applications
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on demand.</p>
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<p><strong>NOTE</strong> - The value for this property will be
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inherited from the <code>reloadable</code> attribute you set on
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the surrounding <a href="context.html">Context</a> component,
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and any value you explicitly set here will be replaced.</p>
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</td></tr></table>
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</div></div>
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<div class="subsection"><h4 id="Standard_Implementation">Standard Implementation</h4><div class="text">
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<p>The standard implementation of <strong>Loader</strong> is
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<strong>org.apache.catalina.loader.WebappLoader</strong>.
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It supports the following additional attributes (in addition to the
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common attributes listed above):</p>
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<table class="defaultTable"><tr><th style="width: 15%;">
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Attribute
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</th><th style="width: 85%;">
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Description
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</th></tr><tr><td><code class="attributeName">loaderClass</code></td><td>
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<p>Java class name of the <code>java.lang.ClassLoader</code>
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implementation class to use. Custom implementations must extend
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<code>org.apache.catalina.loader.WebappClassLoaderBase</code>.
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</p>
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<p>If not specified, the default value is
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<code>org.apache.catalina.loader.WebappClassLoader</code>. The
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default <strong>loaderClass</strong> is not parallel capable, which
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means that loading a class from this classloader is performed by one
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thread at a time. A parallel capable <strong>loaderClass</strong> is
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available and can be used by specifying
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<code>org.apache.catalina.loader.ParallelWebappClassLoader</code>.</p>
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</td></tr></table>
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</div></div>
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</div><h3 id="Nested_Components">Nested Components</h3><div class="text">
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<p>No components may be nested inside a <strong>Loader</strong> element.</p>
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</div><h3 id="Special_Features">Special Features</h3><div class="text">
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<div class="subsection"><h4 id="Logging">Logging</h4><div class="text">
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<p>A loader is associated with the log category based on its classname.</p>
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</div></div>
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</div><div class="noprint"><h3 id="comments_section">
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Comments
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</h3><div class="text"><p class="notice"><strong>Notice: </strong>This comments section collects your suggestions
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on improving documentation for Apache Tomcat.<br><br>
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If you have trouble and need help, read
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<a href="https://tomcat.apache.org/findhelp.html">Find Help</a> page
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and ask your question on the tomcat-users
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<a href="https://tomcat.apache.org/lists.html">mailing list</a>.
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Do not ask such questions here. This is not a Q&A section.<br><br>
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The Apache Comments System is explained <a href="../comments.html">here</a>.
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Comments may be removed by our moderators if they are either
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implemented or considered invalid/off-topic.
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