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<!DOCTYPE document [
<!ENTITY project SYSTEM "project.xml">
]>
<document url="loader.html">
&project;
<properties>
<author email="[email protected]">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>
<p><em>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 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.</em></p>
</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>
</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. Custom implementations must extend
<code>org.apache.catalina.loader.WebappClassLoaderBase</code>.
</p>
<p>If not specified, the default value is
<code>org.apache.catalina.loader.ParallelWebappClassLoader</code>. The
default <strong>loaderClass</strong> is parallel capable, which
means that multiple threads may load difference classes in parallel.
A non-parallel capable <strong>loaderClass</strong> is available and can
be used by specifying
<code>org.apache.catalina.loader.WebappClassLoader</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>
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