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<!DOCTYPE document [
<!ENTITY project SYSTEM "project.xml">
]>
<document url="resources.html">
&project;
<properties>
<title>The Resources Component</title>
</properties>
<body>
<section name="Table of Contents">
<toc />
</section>
<section name="Introduction">
<p>The <strong>Resources</strong> element represents all the resources
available to the web application. This includes classes, JAR files, HTML, JSPs
and any other files that contribute to the web application. Implementations
are provided to use directories, JAR files and WARs as the source of these
resources and the resources implementation may be extended to provide support
for files stored in other forms such as in a database or a versioned
repository.</p>
<p>Resources are cached by default.</p>
<p><strong>Note: Running a webapp with non-filesystem based
Resources implementations is only possible when the webapp does not
rely on direct filesystem access to its own resources, and uses the methods
in the ServletContext interface to access them.</strong></p>
<p>A Resources element MAY be nested inside a
<a href="context.html">Context</a> component. If it is not included,
a default filesystem based Resources will be created automatically,
which is sufficient for most requirements.</p>
</section>
<section name="Attributes">
<subsection name="Common Attributes">
<p>All implementations of <strong>Resources</strong> support the following
attributes:</p>
<attributes>
<attribute name="allowLinking" required="false">
<p>If the value of this flag is <code>true</code>, symlinks will be
allowed inside the web application, pointing to resources inside or
outside the web application base path. If not specified, the default
value of the flag is <code>false</code>.</p>
<p><b>NOTE: This flag MUST NOT be set to true on the Windows platform
(or any other OS which does not have a case sensitive filesystem),
as it will disable case sensitivity checks, allowing JSP source code
disclosure, among other security problems.</b></p>
</attribute>
<attribute name="archiveIndexStrategy" required="false">
<p>If this is <code>simple</code> then a hash map will be used for
JAR archive lookups.</p>
<p>If this is <code>bloom</code> then a bloom filter will be used to
speed up archive lookups. This can be beneficial to the deployment
speed to web applications that contain very large amount of JARs.</p>
<p>If this is <code>purged</code> then a bloom filter will be used to
speed up archive lookups, but can be purged at runtime. It is recommended
to use <code>bloom</code> to avoid reinitializing the bloom filters.</p>
<p>If not specified, the default value of <code>simple</code> will be
used.</p>
</attribute>
<attribute name="cacheMaxSize" required="false">
<p>The maximum size of the static resource cache in kilobytes.
If not specified, the default value is <code>10240</code>
(10 MiB). This value may be changed while the web application is
running (e.g. via JMX). If the cache is using more memory than the new
limit the cache will attempt to reduce in size over time to meet the
new limit. If necessary, <strong>cacheObjectMaxSize</strong> will be
reduced to ensure that it is no larger than
<code>cacheMaxSize/20</code>.</p>
</attribute>
<attribute name="cacheObjectMaxSize" required="false">
<p>Maximum size of the static resource that will be placed in the cache.
If not specified, the default value is <code>512</code>
(512 kilobytes). If this value is greater than
<code>cacheMaxSize/20</code> it will be reduced to
<code>cacheMaxSize/20</code>. This value may be changed while the web
application is running (e.g. via JMX).</p>
</attribute>
<attribute name="cacheTtl" required="false">
<p>The amount of time in milliseconds between the revalidation of cache
entries. If not specified, the default value is <code>5000</code> (5
seconds). This value may be changed while the web application is running
(e.g. via JMX). When a resource is cached it will inherit the TTL in
force at the time it was cached and retain that TTL until the resource
is evicted from the cache regardless of any subsequent changes that may
be made to this attribute.</p>
</attribute>
<attribute name="cachingAllowed" required="false">
<p>If the value of this flag is <code>true</code>, the cache for static
resources will be used. If not specified, the default value
of the flag is <code>true</code>. This value may be changed while the
web application is running (e.g. via JMX). When the cache is disabled
any resources currently in the cache are cleared from the cache.</p>
</attribute>
<attribute name="className" required="false">
<p>Java class name of the implementation to use. This class must
implement the <code>org.apache.catalina.WebResourceRoot</code>
interface. If not specified, the standard value (defined below) will be
used.</p>
</attribute>
<attribute name="readOnly" required="false">
<p>If the value of this flag is <code>true</code>, then writing will
be disabled on the main resource set. The default value is
<code>false</code>.</p>
</attribute>
<attribute name="trackLockedFiles" required="false">
<p>Controls whether the track locked files feature is enabled. If
enabled, all calls to methods that return objects that lock a file and
need to be closed to release that lock (e.g.
<code>ServletContext.getResourceAsStream()</code>) will perform a number
of additional tasks.</p>
<ul>
<li>The stack trace at the point where the method was called will be
recorded and associated with the returned object.</li>
<li>The returned object will be wrapped so that the point where
close() (or equivalent) is called to release the resources can be
detected. Tracking of the object will cease once the resources have
been released.</li>
<li>All remaining locked resources on web application shutdown will be
logged and then closed.</li>
</ul>
<p>If not specified, the default value of <code>false</code> will be
used.</p>
</attribute>
</attributes>
</subsection>
<subsection name="Standard Implementation">
<h3>Standard Root Implementation</h3>
<p>The standard implementation of <strong>Resources</strong> is
<strong>org.apache.catalina.webresources.StandardRoot</strong>. It does not
support any additional attributes.</p>
<h3>Extracting Root Implementation</h3>
<p>The extracting implementation of <strong>Resources</strong> is
<strong>org.apache.catalina.webresources.ExtractingRoot</strong>. It does not
support any additional attributes.</p>
<p>When deploying web applications as packed WAR files, the extracting root
will extract any JAR files from <code>/WEB-INF/lib</code> to a
<code>application-jars</code> directory located in the web
application's working directory. These extracted JARs will be removed
when the web application stops.</p>
<p>Extracting JAR files from a packed WAR may provide a performance
improvement, particularly at web application start when JAR scanning is
required by the application.</p>
</subsection>
</section>
<section name="Nested Components">
<p>A web application's main resources are defined by the
<strong>docBase</strong> defined for the <a href="context.html">Context</a>.
Additional configuration settings and/or resources may be made available to
the web application by defining one or more nested components.</p>
<h3>PreResources</h3>
<p>PreResources are searched before the main resources. They will be searched
in the order they are defined. To configure PreResources, nest a
<PreResources> element inside the <Resources> element with the
following attributes:</p>
<attributes>
<attribute name="allowLinking" required="false">
<p>If the value of this flag is <code>true</code>, symlinks will be
allowed inside the web resource set, pointing to resources inside or
outside the web application base path. If not specified, the default
value of the flag is taken from the outer Resources implementation.</p>
<p>This attribute is only available for <code>DirResourceSet</code> and
<code>FileResourceSet</code>.</p>
<p><b>NOTE: This flag MUST NOT be set to true on the Windows platform
(or any other OS which does not have a case sensitive filesystem),
as it will disable case sensitivity checks, allowing JSP source code
disclosure, among other security problems.</b></p>
</attribute>
<attribute name="base" required="true">
<p>Identifies where the resources to be used are located. This attribute
is required by the <code>org.apache.catalina.WebResourceSet</code>
implementations provided by Tomcat and should specify the absolute path to
the file, directory or JAR where the resources are located. Custom
implementations may not require it.</p>
</attribute>
<attribute name="className" required="true">
<p>Java class name of the implementation to use. This class must
implement the <code>org.apache.catalina.WebResourceSet</code> interface.
Tomcat provides three standard implementations:
<code>org.apache.catalina.webresources.DirResourceSet</code>,
<code>org.apache.catalina.webresources.FileResourceSet</code> and
<code>org.apache.catalina.webresources.JarResourceSet</code>. Custom
implementations may also be used.
</p>
</attribute>
<attribute name="internalPath" required="false">
<p>Identifies the path within the <strong>base</strong> where the
resources are to be found. This is typically only used with JAR files when
the resources are not located at the root of the JAR as is the case with
resource JARs. This attribute is required by the
<code>org.apache.catalina.WebResourceSet</code> implementations provided
by Tomcat and must start with '/'. Custom implementations may not require
it. If not specified, the default value '/' will be used.</p>
</attribute>
<attribute name="readOnly" required="false">
<p>If <code>true</code>, resources within this resource set may not be
deleted, created or modified. For instance of
<code>org.apache.catalina.webresources.JarResourceSet</code>, this
attribute is hard-coded to <code>true</code> and may not be changed. For
instances of <code>org.apache.catalina.webresources.DirResourceSet</code>
and <code>org.apache.catalina.webresources.FileResourceSet</code> the
default value of this attribute is <code>false</code>.</p>
</attribute>
<attribute name="webAppMount" required="false">
<p>Identifies the path within the web application that these resources
will be made available. For the
<code>org.apache.catalina.WebResourceSet</code> implementations provided
by Tomcat, this attribute is required and must start with '/'. Custom
implementations may not require it. If not specified, the default value of
'/' will be used.</p>
</attribute>
</attributes>
<h3>JAR resources</h3>
<p>JarResources are searched after the main resources but before the
PostResources. They will be searched in the order they are defined. To
configure JarResources, nest a <JarResources> element inside the
<Resources> element. The configuration attributes are the same as for
<strong>PreResources</strong>.
</p>
<p>During web application start, the JAR scanning process checks scanned JARs
for content under <code>/META-INF/resources</code>. Where found, this static
content is added to the JarResources.
</p>
<h3>Post-resources</h3>
<p>PostResources are searched after the resource JARs. They will be searched
in the order they are defined. To configure PostResources, nest a
<PostResources> element inside the <Resources> element. The
configuration attributes are the same as for <strong>PreResources</strong>.
</p>
<h3>Ordering</h3>
<p>In addition to the sets of resources described above, the standard
implementation also maintains ClassResources which represent the classes
contained in the JAR files mapped to <code>/WEB-INF/classes</code>. This
allows other components to search for classes with a single call rather than
one call to search <code>/WEB-INF/classes</code> followed by another to search
the JARs in <code>/WEB-INF/lib</code>. The ClassResources are populated
from the JARs mapped to <code>/WEB-INF/lib</code> when the web application
starts.</p>
<p>Therefore, the complete search order is:</p>
<ul>
<li>PreResources</li>
<li>MainResources</li>
<li>ClassResources</li>
<li>JarResources</li>
<li>PostResources</li>
</ul>
<p>The population of ClassResources and JarResources at web application start
means that care needs to be taken to add JAR based resources correctly to
obtain the desired behaviour. Consider the following example:</p>
<source><![CDATA[<Resources>
<PostResources base="D:\Projects\external\classes"
className="org.apache.catalina.webresources.DirResourceSet"
webAppMount="/WEB-INF/classes"/>
<PostResources base="D:\Projects\lib\library1.jar"
className="org.apache.catalina.webresources.FileResourceSet"
webAppMount="/WEB-INF/lib/library1.jar"/>
</Resources>]]></source>
<p>Since both resources are PostResources, it might be expected that
<code>D:\Projects\external\classes</code> will be searched for classes before
<code>D:\Projects\lib\library1.jar</code>. However, by adding the JAR using a
<code>FileResourceSet</code>, the JAR is mapped to <code>/WEB-INF/lib</code>
and will be processed at application start along with the other JARs in
<code>/WEB-INF/lib</code>. The classes from the JAR file will be added to the
ClassResources which means they will be searched before the classes from
<code>D:\Projects\external\classes</code>. If the desired behaviour is that
<code>D:\Projects\external\classes</code> is searched before
<code>D:\Projects\lib\library1.jar</code> then a slightly different
configuration is required:</p>
<source><![CDATA[<Resources>
<PostResources base="D:\Projects\external\classes"
className="org.apache.catalina.webresources.DirResourceSet"
webAppMount="/WEB-INF/classes"/>
<PostResources base="D:\Projects\lib\library1.jar"
className="org.apache.catalina.webresources.JarResourceSet"
webAppMount="/WEB-INF/classes"/>
</Resources>]]></source>
<p>In short, the JAR file should be added as a <code>JarResourceSet</code>
mapped to <code>/WEB-INF/classes</code> rather than using a
<code>FileResourceSet</code> mapped to <code>/WEB-INF/lib</code>.
</p>
<h3>Cache Strategy</h3>
<p>Additional control over the caching of static resources can be obtained by
configuring a custom cache strategy. To configure a custom cache strategy,
nest a <CacheStrategy> element inside the <Resources> element
with 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.WebResourceRoot$CacheStrategy</code>
interface.</p>
</attribute>
</attributes>
</section>
<section name="Special Features">
<p>No special features are associated with a <strong>Resources</strong>
element.</p>
</section>
</body>
</document>