container/webapps/docs/class-loader-howto.xml - tomcat55 - Git at Google

 <?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.
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 <!DOCTYPE document [
   <!ENTITY project SYSTEM "project.xml">
 ]>
 <document url="class-loader-howto.html">

     &project;

     <properties>
         <author email="craigmcc@apache.org">Craig R. McClanahan</author>
         <author email="yoavs@apache.org">Yoav Shapira</author>
         <title>Class Loader HOW-TO</title>
     </properties>

 <body>

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

 <section name="Quick Start">

 <p>The following rules cover about 95% of the decisions that application
 developers and deployers must make about where to place class and resource
 files to make them available to web applications:</p>
 <ul>
 <li>For classes and resources specific to a particular web application,
     place unpacked classes and resources under <code>/WEB-INF/classes</code>
     of your web application archive, or place JAR files containing those
     classes and resources under <code>/WEB-INF/lib</code> of your web
     application archive.</li>
 <li>For classes and resources that must be shared across all web applications,
     place unpacked classes and resources under
     <code>$CATALINA_BASE/shared/classes</code>, or place JAR files
     containing those classes and resources under
     <code>$CATALINA_BASE/shared/lib</code>.</li>
 </ul>

 </section>


 <section name="Overview">

 <p>Like many server applications, Tomcat 5 installs a variety of class loaders
 (that is, classes that implement <code>java.lang.ClassLoader</code>) to allow
 different portions of the container, and the web applications running on the
 container, to have access to different repositories of available classes and
 resources.  This mechanism is used to provide the functionality defined in the
 Servlet Specification, version 2.4 -- in particular, Sections 9.4 and 9.6.</p>

 <p>In a J2SE 2 (that is, J2SE 1.2 or later) environment, class loaders are
 arranged in a parent-child tree.  Normally, when a class loader is asked to
 load a particular class or resource, it delegates the request to a parent
 class loader first, and then looks in its own repositories only if the parent
 class loader(s) cannot find the requested class or resource.  The model for
 web application class loaders differs slightly from this, as discussed below,
 but the main principles are the same.</p>

 <p>When Tomcat 5 is started, it creates a set of class loaders that are
 organized into the following parent-child relationships, where the parent
 class loader is above the child class loader:</p>

 <source>
       Bootstrap
           |
        System
           |
        Common
       /      \
  Catalina   Shared
              /   \
         Webapp1  Webapp2 ...
 </source>

 <p>The characteristics of each of these class loaders, including the source
 of classes and resources that they make visible, are discussed in detail in
 the following section.</p>

 </section>

 <section name="Class Loader Definitions">

 <p>As indicated in the diagram above, Tomcat 5 creates the following class
 loaders as it is initialized:</p>
 <ul>
 <li><strong>Bootstrap</strong> - This class loader contains the basic runtime
     classes provided by the Java Virtual Machine, plus any classes from JAR
     files present in the System Extensions directory
     (<code>$JAVA_HOME/jre/lib/ext</code>).  <em>NOTE</em> - Some JVMs may
     implement this as more than one class loader, or it may not be visible
     (as a class loader) at all.</li>
 <li><strong>System</strong> - This class loader is normally initialized from
     the contents of the <code>CLASSPATH</code> environment variable.  All such
     classes are visible to both Tomcat internal classes, and to web
     applications.  However, the standard Tomcat 5 startup scripts
     (<code>$CATALINA_HOME/bin/catalina.sh</code> or
     <code>%CATALINA_HOME%\bin\catalina.bat</code>) totally ignore the contents
     of the <code>CLASSPATH</code> environment variable itself, and instead
     build the System class loader from the following repositories:
     <ul>
     <li><em>$CATALINA_HOME/bin/bootstrap.jar</em> - Contains the main() method
         that is used to initialize the Tomcat 5 server, and the class loader
         implementation classes it depends on.</li>
     <li><em>$JAVA_HOME/lib/tools.jar</em> - Contains the "javac" compiler used
         to convert JSP pages into servlet classes.</li>
     <li><em>$CATALINA_HOME/bin/commons-logging-api-x.y.z.jar</em> - Jakarta
         commons logging API.</li>
     <li><em>$CATALINA_HOME/bin/commons-daemon.jar</em> - Jakarta commons
         daemon API.</li>
     <li><em>jmx.jar</em> - The JMX 1.2 implementation.</li>
     </ul></li>
 <li><strong>Common</strong> - This class loader contains additional classes
     that are made visible to both Tomcat internal classes and to all web
     applications.  Normally, application classes should <strong>NOT</strong>
     be placed here.  All unpacked classes and resources in
     <code>$CATALINA_HOME/common/classes</code>, as well as classes and
     resources in JAR files under the
     <code>$CATALINA_HOME/commons/endorsed</code>,
     <code>$CATALINA_HOME/commons/i18n</code> and
     <code>$CATALINA_HOME/common/lib</code> directories,
     are made visible through this
     class loader.  By default, that includes the following:
     <ul>
     <li><em>commons-el.jar</em> - Jakarta commons el, implementing the
         expression language used by Jasper.</li>
     <li><em>ecj-x.y.x.jar</em> - The Eclipse JDT Java compiler.</li>
     <li><em>jasper-compiler.jar</em> - The JSP 2.0 compiler.</li>
     <li><em>jasper-runtime.jar</em> - The JSP 2.0 runtime.</li>
     <li><em>jsp-api.jar</em> - The JSP 2.0 API.</li>
     <li><em>naming-common.jar</em> - The JNDI implementation used by Tomcat 5
         to represent in-memory naming contexts.</li>
     <li><em>naming-factory.jar</em> - The JNDI implementation used by Tomcat 5
         to resolve references to enterprise resources (EJB, connection
         pools).</li>
     <li><em>naming-factory-dbcp.jar</em> - Jakarta commons DBCP, providing a
         JDBC connection pool to web applications. The classes have been moved
         out of their default org.apache.commons package.</li>
     <li><em>naming-java.jar</em> - Handler for the java: namespace.</li>
     <li><em>naming-resources.jar</em> - The specialized JNDI naming context
         implementation used to represent the static resources of a web
         application. This is not related to the support of the J2EE ENC, and
         cannot be removed.</li>
     <li><em>servlet-api.jar</em> - The Servlet 2.4 API.</li>
     <li><em>tomcat-i18n-**.jar</em> - Optional JARs containing resource bundles
         for other languages. As default bundles are also included in each
         individual JAR, they can be safely removed if no internationalization
         of messages is needed.</li>
     </ul></li>
 <li><strong>Catalina</strong> - This class loader is initialized to include
     all classes and resources required to implement Tomcat 5 itself.  These
     classes and resources are <strong>TOTALLY</strong> invisible to web
     applications.  All unpacked classes and resources in
     <code>$CATALINA_HOME/server/classes</code>, as well as classes and
     resources in JAR files under
     <code>$CATALINA_HOME/server/lib</code>, are made visible through
     this class loader.  By default, that includes the following:
     <ul>
     <li><em>catalina.jar</em> - Implementation of the Catalina servlet
         container portion of Tomcat 5.</li>
     <li><em>catalina-ant.jar</em> - Some Ant tasks which can be used to
         manage Tomcat using the manager web application.</li>
     <li><em>catalina-optional.jar</em> - Some optional components of
         Catalina.</li>
     <li><em>commons-modeler.jar</em> - A model MBeans implementation used
         by Tomcat to expose its internal objects through JMX.</li>
     <li><em>servlets-xxxxx.jar</em> - The classes associated with each
         internal servlet that provides part of Tomcat's functionality.
         These are separated so that they can be completely removed if the
         corresponding service is not required, or they can be subject to
         specialized security manager permissions.</li>
     <li><em>tomcat-coyote.jar</em> - Coyote API.</li>
     <li><em>tomcat-http.jar</em> - Standalone Java HTTP/1.1
         connector.</li>
     <li><em>tomcat-ajp.jar</em> - Classes for the Java portion of the
         <code>AJP</code> web server connector, which allows Tomcat to
         run behind web servers such as Apache and iPlanet iAS and iWS.</li>
     <li><em>tomcat-util.jar</em> - Utility classes required by some
         Tomcat connectors.</li>
     </ul></li>
 <li><strong>Shared</strong> - This class loader is the place to put classes
     and resources that you wish to share across <strong>ALL</strong>
     web applications (unless Tomcat internal classes also need access,
     in which case you should put them in the <strong>Common</strong>
     class loader instead).  All unpacked classes and resources in
     <code>$CATALINA_BASE/shared/classes</code>, as well as classes and
     resources in JAR files under <code>$CATALINA_BASE/shared/lib</code>, are
     made visible through this class loader. If multiple Tomcat instances are
     run from the same binary using the $CATALINA_BASE environment variable,
     then this classloader repositories are relative to $CATALINA_BASE rather
     than $CATALINA_HOME.</li>
 <li><strong>WebappX</strong> - A class loader is created for each web
     application that is deployed in a single Tomcat 5 instance.  All unpacked
     classes and resources in the <code>/WEB-INF/classes</code> directory of
     your web application archive, plus classes and resources in JAR files
     under the <code>/WEB-INF/lib</code> directory of your web application
     archive, are made visible to the containing web application, but to
     no others.</li>
 </ul>

 <p>As mentioned above, the web application class loader diverges from the
 default Java 2 delegation model (in accordance with the recommendations in the
 Servlet Specification, version 2.3, section 9.7.2 Web Application Classloader).
 When a request to load a
 class from the web application's <em>WebappX</em> class loader is processed,
 this class loader will look in the local repositories <strong>first</strong>,
 instead of delegating before looking.  There are exceptions. Classes which are
 part of the JRE base classes cannot be overriden. For some classes (such as
 the XML parser components in J2SE 1.4+), the J2SE 1.4 endorsed feature can be
 used
 (see the common classloader definition above).
 Last, any JAR containing servlet API classes will be ignored by the
 classloader.
 All other class loaders in Tomcat 5 follow the usual delegation pattern.</p>

 <p>Therefore, from the perspective of a web application, class or resource
 loading looks in the following repositories, in this order:</p>
 <ul>
 <li>Bootstrap classes of your JVM</li>
 <li>System class loader classes (described above)</li>
 <li><em>/WEB-INF/classes</em> of your web application</li>
 <li><em>/WEB-INF/lib/*.jar</em> of your web application</li>
 <li><em>$CATALINA_HOME/common/classes</em></li>
 <li><em>$CATALINA_HOME/common/endorsed/*.jar</em></li>
 <li><em>$CATALINA_HOME/common/i18n/*.jar</em></li>
 <li><em>$CATALINA_HOME/common/lib/*.jar</em></li>
 <li><em>$CATALINA_BASE/shared/classes</em></li>
 <li><em>$CATALINA_BASE/shared/lib/*.jar</em></li>
 </ul>

 </section>


 <section name="XML Parsers and J2SE 1.4">

 <p>Among many other changes, the J2SE 1.4 release packages the JAXP APIs, and
 a version of Xerces, inside the JRE.  This has impacts on applications that
 wish to use their own XML parser.</p>

 <p>In previous versions of Tomcat 5, you could simply replace the XML parser
 in the <code>$CATALINA_HOME/common/lib</code> directory to change the parser
 used by all web applications.  However, this technique will not be effective
 when you are running on J2SE 1.4, because the usual class loader delegation
 process will always choose the implementation inside the JDK in preference
 to this one.</p>

 <p>JDK 1.4 supports a mechanism called the "Endorsed Standards Override
 Mechanism" to allow replacement of APIs created outside of the JCP (i.e.
 DOM and SAX from W3C).  It can also be used to update the XML parser
 implementation.  For more information, see:
 <a href="http://java.sun.com/j2se/1.4/docs/guide/standards/index.html">
 http://java.sun.com/j2se/1.4/docs/guide/standards/index.html</a>.</p>

 <p>Tomcat utilizes this mechanism by including the system property setting
 <code>-Djava.endorsed.dirs=$CATALINA_HOME/common/endorsed</code> in the
 command line that starts the container.  Therefore, you can replace the
 parser that is installed in this directory, and it will get used even on a
 JDK 1.4 system.</p>

 </section>


 <section name="Running under a security manager">

 <p>When running under a security manager the locations from which classes
 are permitted to be loaded will also depend on the contents of your policy
 file. See <a href="security-manager-howto.html">Security Manager HOW-TO</a>
 for further information.</p>

 </section>


 </body>

 </document>
	<?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="class-loader-howto.html">

	&project;

	<properties>
	<author email="craigmcc@apache.org">Craig R. McClanahan</author>
	<author email="yoavs@apache.org">Yoav Shapira</author>
	<title>Class Loader HOW-TO</title>
	</properties>

	<body>

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

	<section name="Quick Start">

	<p>The following rules cover about 95% of the decisions that application
	developers and deployers must make about where to place class and resource
	files to make them available to web applications:</p>
	<ul>
	<li>For classes and resources specific to a particular web application,
	place unpacked classes and resources under <code>/WEB-INF/classes</code>
	of your web application archive, or place JAR files containing those
	classes and resources under <code>/WEB-INF/lib</code> of your web
	application archive.</li>
	<li>For classes and resources that must be shared across all web applications,
	place unpacked classes and resources under
	<code>$CATALINA_BASE/shared/classes</code>, or place JAR files
	containing those classes and resources under
	<code>$CATALINA_BASE/shared/lib</code>.</li>
	</ul>

	</section>


	<section name="Overview">

	<p>Like many server applications, Tomcat 5 installs a variety of class loaders
	(that is, classes that implement <code>java.lang.ClassLoader</code>) to allow
	different portions of the container, and the web applications running on the
	container, to have access to different repositories of available classes and
	resources. This mechanism is used to provide the functionality defined in the
	Servlet Specification, version 2.4 -- in particular, Sections 9.4 and 9.6.</p>

	<p>In a J2SE 2 (that is, J2SE 1.2 or later) environment, class loaders are
	arranged in a parent-child tree. Normally, when a class loader is asked to
	load a particular class or resource, it delegates the request to a parent
	class loader first, and then looks in its own repositories only if the parent
	class loader(s) cannot find the requested class or resource. The model for
	web application class loaders differs slightly from this, as discussed below,
	but the main principles are the same.</p>

	<p>When Tomcat 5 is started, it creates a set of class loaders that are
	organized into the following parent-child relationships, where the parent
	class loader is above the child class loader:</p>

	<source>
	Bootstrap
	\|
	System
	\|
	Common
	/ \
	Catalina Shared
	/ \
	Webapp1 Webapp2 ...
	</source>

	<p>The characteristics of each of these class loaders, including the source
	of classes and resources that they make visible, are discussed in detail in
	the following section.</p>

	</section>

	<section name="Class Loader Definitions">

	<p>As indicated in the diagram above, Tomcat 5 creates the following class
	loaders as it is initialized:</p>
	<ul>
	<li><strong>Bootstrap</strong> - This class loader contains the basic runtime
	classes provided by the Java Virtual Machine, plus any classes from JAR
	files present in the System Extensions directory
	(<code>$JAVA_HOME/jre/lib/ext</code>). <em>NOTE</em> - Some JVMs may
	implement this as more than one class loader, or it may not be visible
	(as a class loader) at all.</li>
	<li><strong>System</strong> - This class loader is normally initialized from
	the contents of the <code>CLASSPATH</code> environment variable. All such
	classes are visible to both Tomcat internal classes, and to web
	applications. However, the standard Tomcat 5 startup scripts
	(<code>$CATALINA_HOME/bin/catalina.sh</code> or
	<code>%CATALINA_HOME%\bin\catalina.bat</code>) totally ignore the contents
	of the <code>CLASSPATH</code> environment variable itself, and instead
	build the System class loader from the following repositories:
	<ul>
	<li><em>$CATALINA_HOME/bin/bootstrap.jar</em> - Contains the main() method
	that is used to initialize the Tomcat 5 server, and the class loader
	implementation classes it depends on.</li>
	<li><em>$JAVA_HOME/lib/tools.jar</em> - Contains the "javac" compiler used
	to convert JSP pages into servlet classes.</li>
	<li><em>$CATALINA_HOME/bin/commons-logging-api-x.y.z.jar</em> - Jakarta
	commons logging API.</li>
	<li><em>$CATALINA_HOME/bin/commons-daemon.jar</em> - Jakarta commons
	daemon API.</li>
	<li><em>jmx.jar</em> - The JMX 1.2 implementation.</li>
	</ul></li>
	<li><strong>Common</strong> - This class loader contains additional classes
	that are made visible to both Tomcat internal classes and to all web
	applications. Normally, application classes should <strong>NOT</strong>
	be placed here. All unpacked classes and resources in
	<code>$CATALINA_HOME/common/classes</code>, as well as classes and
	resources in JAR files under the
	<code>$CATALINA_HOME/commons/endorsed</code>,
	<code>$CATALINA_HOME/commons/i18n</code> and
	<code>$CATALINA_HOME/common/lib</code> directories,
	are made visible through this
	class loader. By default, that includes the following:
	<ul>
	<li><em>commons-el.jar</em> - Jakarta commons el, implementing the
	expression language used by Jasper.</li>
	<li><em>ecj-x.y.x.jar</em> - The Eclipse JDT Java compiler.</li>
	<li><em>jasper-compiler.jar</em> - The JSP 2.0 compiler.</li>
	<li><em>jasper-runtime.jar</em> - The JSP 2.0 runtime.</li>
	<li><em>jsp-api.jar</em> - The JSP 2.0 API.</li>
	<li><em>naming-common.jar</em> - The JNDI implementation used by Tomcat 5
	to represent in-memory naming contexts.</li>
	<li><em>naming-factory.jar</em> - The JNDI implementation used by Tomcat 5
	to resolve references to enterprise resources (EJB, connection
	pools).</li>
	<li><em>naming-factory-dbcp.jar</em> - Jakarta commons DBCP, providing a
	JDBC connection pool to web applications. The classes have been moved
	out of their default org.apache.commons package.</li>
	<li><em>naming-java.jar</em> - Handler for the java: namespace.</li>
	<li><em>naming-resources.jar</em> - The specialized JNDI naming context
	implementation used to represent the static resources of a web
	application. This is not related to the support of the J2EE ENC, and
	cannot be removed.</li>
	<li><em>servlet-api.jar</em> - The Servlet 2.4 API.</li>
	<li><em>tomcat-i18n-**.jar</em> - Optional JARs containing resource bundles
	for other languages. As default bundles are also included in each
	individual JAR, they can be safely removed if no internationalization
	of messages is needed.</li>
	</ul></li>
	<li><strong>Catalina</strong> - This class loader is initialized to include
	all classes and resources required to implement Tomcat 5 itself. These
	classes and resources are <strong>TOTALLY</strong> invisible to web
	applications. All unpacked classes and resources in
	<code>$CATALINA_HOME/server/classes</code>, as well as classes and
	resources in JAR files under
	<code>$CATALINA_HOME/server/lib</code>, are made visible through
	this class loader. By default, that includes the following:
	<ul>
	<li><em>catalina.jar</em> - Implementation of the Catalina servlet
	container portion of Tomcat 5.</li>
	<li><em>catalina-ant.jar</em> - Some Ant tasks which can be used to
	manage Tomcat using the manager web application.</li>
	<li><em>catalina-optional.jar</em> - Some optional components of
	Catalina.</li>
	<li><em>commons-modeler.jar</em> - A model MBeans implementation used
	by Tomcat to expose its internal objects through JMX.</li>
	<li><em>servlets-xxxxx.jar</em> - The classes associated with each
	internal servlet that provides part of Tomcat's functionality.
	These are separated so that they can be completely removed if the
	corresponding service is not required, or they can be subject to
	specialized security manager permissions.</li>
	<li><em>tomcat-coyote.jar</em> - Coyote API.</li>
	<li><em>tomcat-http.jar</em> - Standalone Java HTTP/1.1
	connector.</li>
	<li><em>tomcat-ajp.jar</em> - Classes for the Java portion of the
	<code>AJP</code> web server connector, which allows Tomcat to
	run behind web servers such as Apache and iPlanet iAS and iWS.</li>
	<li><em>tomcat-util.jar</em> - Utility classes required by some
	Tomcat connectors.</li>
	</ul></li>
	<li><strong>Shared</strong> - This class loader is the place to put classes
	and resources that you wish to share across <strong>ALL</strong>
	web applications (unless Tomcat internal classes also need access,
	in which case you should put them in the <strong>Common</strong>
	class loader instead). All unpacked classes and resources in
	<code>$CATALINA_BASE/shared/classes</code>, as well as classes and
	resources in JAR files under <code>$CATALINA_BASE/shared/lib</code>, are
	made visible through this class loader. If multiple Tomcat instances are
	run from the same binary using the $CATALINA_BASE environment variable,
	then this classloader repositories are relative to $CATALINA_BASE rather
	than $CATALINA_HOME.</li>
	<li><strong>WebappX</strong> - A class loader is created for each web
	application that is deployed in a single Tomcat 5 instance. All unpacked
	classes and resources in the <code>/WEB-INF/classes</code> directory of
	your web application archive, plus classes and resources in JAR files
	under the <code>/WEB-INF/lib</code> directory of your web application
	archive, are made visible to the containing web application, but to
	no others.</li>
	</ul>

	<p>As mentioned above, the web application class loader diverges from the
	default Java 2 delegation model (in accordance with the recommendations in the
	Servlet Specification, version 2.3, section 9.7.2 Web Application Classloader).
	When a request to load a
	class from the web application's <em>WebappX</em> class loader is processed,
	this class loader will look in the local repositories <strong>first</strong>,
	instead of delegating before looking. There are exceptions. Classes which are
	part of the JRE base classes cannot be overriden. For some classes (such as
	the XML parser components in J2SE 1.4+), the J2SE 1.4 endorsed feature can be
	used
	(see the common classloader definition above).
	Last, any JAR containing servlet API classes will be ignored by the
	classloader.
	All other class loaders in Tomcat 5 follow the usual delegation pattern.</p>

	<p>Therefore, from the perspective of a web application, class or resource
	loading looks in the following repositories, in this order:</p>
	<ul>
	<li>Bootstrap classes of your JVM</li>
	<li>System class loader classes (described above)</li>
	<li><em>/WEB-INF/classes</em> of your web application</li>
	<li><em>/WEB-INF/lib/*.jar</em> of your web application</li>
	<li><em>$CATALINA_HOME/common/classes</em></li>
	<li><em>$CATALINA_HOME/common/endorsed/*.jar</em></li>
	<li><em>$CATALINA_HOME/common/i18n/*.jar</em></li>
	<li><em>$CATALINA_HOME/common/lib/*.jar</em></li>
	<li><em>$CATALINA_BASE/shared/classes</em></li>
	<li><em>$CATALINA_BASE/shared/lib/*.jar</em></li>
	</ul>

	</section>


	<section name="XML Parsers and J2SE 1.4">

	<p>Among many other changes, the J2SE 1.4 release packages the JAXP APIs, and
	a version of Xerces, inside the JRE. This has impacts on applications that
	wish to use their own XML parser.</p>

	<p>In previous versions of Tomcat 5, you could simply replace the XML parser
	in the <code>$CATALINA_HOME/common/lib</code> directory to change the parser
	used by all web applications. However, this technique will not be effective
	when you are running on J2SE 1.4, because the usual class loader delegation
	process will always choose the implementation inside the JDK in preference
	to this one.</p>

	<p>JDK 1.4 supports a mechanism called the "Endorsed Standards Override
	Mechanism" to allow replacement of APIs created outside of the JCP (i.e.
	DOM and SAX from W3C). It can also be used to update the XML parser
	implementation. For more information, see:
	<a href="http://java.sun.com/j2se/1.4/docs/guide/standards/index.html">
	http://java.sun.com/j2se/1.4/docs/guide/standards/index.html</a>.</p>

	<p>Tomcat utilizes this mechanism by including the system property setting
	<code>-Djava.endorsed.dirs=$CATALINA_HOME/common/endorsed</code> in the
	command line that starts the container. Therefore, you can replace the
	parser that is installed in this directory, and it will get used even on a
	JDK 1.4 system.</p>

	</section>


	<section name="Running under a security manager">

	<p>When running under a security manager the locations from which classes
	are permitted to be loaded will also depend on the contents of your policy
	file. See <a href="security-manager-howto.html">Security Manager HOW-TO</a>
	for further information.</p>

	</section>


	</body>

	</document>