<?xml version="1.0"?> <!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. --> <!DOCTYPE document [ <!ENTITY project SYSTEM "project.xml"> ]> <document url="loader.html"> &project; <properties> <author email="craigmcc@apache.org">Craig R. McClanahan</author> <title>The Loader Component</title> </properties> <body> <section name="Table of Contents"> <toc/> </section> <section name="Introduction"> <p>The <strong>Loader</strong> element represents the <em>web application class loader</em> that will be used to load Java classes and resources for your web application. Such a class loader must follow the requirements of the Servlet Specification, and load classes from the following locations:</p> <ul> <li>From the <code>/WEB-INF/classes</code> directory inside your web application.</li> <li>From JAR files in the <code>/WEB-INF/lib</code> directory inside your web application.</li> <li>From resources made available by Catalina to all web applications globally.</li> </ul> <p>A Loader element MAY be nested inside a <a href="context.html">Context</a> component. If it is not included, a default Loader configuration will be created automatically, which is sufficient for most requirements.</p> <p>For a more in-depth description of the class loader hierarchy that is implemented by Catalina, see <a href="../class-loader-howto.html">the ClassLoader HowTo</a>.</p> <blockquote><em> <p>The description below uses the variable name $CATALINA_BASE to refer the base directory against which most relative paths are resolved. If you have not configured Tomcat 6 for multiple instances by setting a CATALINA_BASE directory, then $CATALINA_BASE will be set to the value of $CATALINA_HOME, the directory into which you have installed Tomcat 6.</p> </em></blockquote> </section> <section name="Attributes"> <subsection name="Common Attributes"> <p>All implementations of <strong>Loader</strong> support the following attributes:</p> <attributes> <attribute name="className" required="false"> <p>Java class name of the implementation to use. This class must implement the <code>org.apache.catalina.Loader</code> interface. If not specified, the standard value (defined below) will be used.</p> </attribute> <attribute name="delegate" required="false"> <p>Set to <code>true</code> if you want the class loader to follow the standard Java2 delegation model, and attempt to load classes from parent class loaders <strong>before</strong> looking inside the web application. Set to <code>false</code> (the default) to have the class loader look inside the web application first, before asking parent class loaders to find requested classes or resources.</p> </attribute> <attribute name="reloadable" required="false"> <p>Set to <code>true</code> if you want Catalina to monitor classes in <code>/WEB-INF/classes/</code> and <code>/WEB-INF/lib</code> for changes, and automatically reload the web application if a change is detected. This feature is very useful during application development, but it requires significant runtime overhead and is not recommended for use on deployed production applications. You can use the <a href="../manager-howto.html">Manager</a> web application, however, to trigger reloads of deployed applications on demand.</p> <p><strong>NOTE</strong> - The value for this property will be inherited from the <code>reloadable</code> attribute you set on the surrounding <a href="context.html">Context</a> component, and any value you explicitly set here will be replaced.</p> </attribute> </attributes> </subsection> <subsection name="Standard Implementation"> <p>The standard implementation of <strong>Loader</strong> is <strong>org.apache.catalina.loader.WebappLoader</strong>. It supports the following additional attributes (in addition to the common attributes listed above):</p> <attributes> <attribute name="loaderClass" required="false"> <p>Java class name of the <code>java.lang.ClassLoader</code> implementation class to use. If not specified, the default value is <code>org.apache.catalina.loader.WebappClassLoader</code>. Custom <strong>loaderClass</strong> implementations must extend <code>org.apache.catalina.loader.WebappClassLoader</code>.</p> </attribute> <attribute name="searchExternalFirst" required="false"> <p>Set to <code>true</code> if you want repositories outside of <code>WEB-INF/classes</code> and <code>WEB-INF/lib</code> to be searched first. Default value is <code>false</code>.</p> </attribute> </attributes> </subsection> </section> <section name="Nested Components"> <p>No components may be nested inside a <strong>Loader</strong> element.</p> </section> <section name="Special Features"> <subsection name="Logging"> <p>A loader is associated with the log category based on its classname.</p> </subsection> </section> </body> </document>