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<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Catalina Functional Specifications - Invoker Servlet</title><meta name="author" value="Craig McClanahan"><meta name="email" value="craigmcc@apache.org"></head><body bgcolor="#ffffff" text="#000000" link="#525D76" alink="#525D76" vlink="#525D76"><table border="0" width="100%" cellspacing="0"><!--PAGE HEADER--><tr><td><!--PROJECT LOGO--><a href="http://tomcat.apache.org/"><img src="../../images/tomcat.gif" align="right" alt="
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Catalina Functional Specifications
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" border="0"></a></td><td><font face="arial,helvetica,sanserif"><h1>Apache Tomcat 6.0</h1></font></td><td><!--APACHE LOGO--><a href="http://www.apache.org/"><img src="../../images/asf-logo.gif" align="right" alt="Apache Logo" border="0"></a></td></tr></table><table border="0" width="100%" cellspacing="4"><!--HEADER SEPARATOR--><tr><td colspan="2"><hr noshade="noshade" size="1"></td></tr><tr><!--LEFT SIDE NAVIGATION--><td width="20%" valign="top" nowrap="true"><p><strong>Links</strong></p><ul><li><a href="../../index.html">Docs Home</a></li><li><a href="index.html">Functional Specs</a></li></ul><p><strong>Administrative Apps</strong></p><ul><li><a href="fs-admin-apps.html">Overall Requirements</a></li><li><a href="mbean-names.html">Tomcat MBean Names</a></li><li><a href="fs-admin-objects.html">Administered Objects</a></li><li><a href="fs-admin-opers.html">Supported Operations</a></li></ul><p><strong>Internal Servlets</strong></p><ul><li><a href="fs-default.html">Default Servlet</a></li><li><a href="fs-invoker.html">Invoker Servlet</a></li></ul><p><strong>Realm Implementations</strong></p><ul><li><a href="fs-jdbc-realm.html">JDBC Realm</a></li><li><a href="fs-jndi-realm.html">JNDI Realm</a></li><li><a href="fs-memory-realm.html">Memory Realm</a></li></ul></td><!--RIGHT SIDE MAIN BODY--><td width="80%" valign="top" align="left"><table border="0" width="100%" cellspacing="4"><tr><td align="left" valign="top"><h1>Catalina Functional Specifications</h1><h2>Invoker Servlet</h2></td><td align="right" valign="top" nowrap="true"><small><a href="printer/fs-invoker.html"><img src="../../images/printer.gif" border="0" alt="Printer Friendly Version"><br>print-friendly<br>version
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</a></small></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Overview"><strong>Overview</strong></a></font></td></tr><tr><td><blockquote>
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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Introduction"><strong>Introduction</strong></a></font></td></tr><tr><td><blockquote>
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<p>The purpose of the <strong>Invoker Servlet</strong> is to allow a
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web application to dynamically register new <em>servlet definitions</em>
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that correspond with a <code><servlet></code> element in the
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<code>/WEB-INF/web.xml</code> deployment descriptor, and execute
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requests utilizing the new servlet definitions. From the perspective
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of the newly registered servlets, all servlet lifecycle requirements
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of the Servlet Specification (such as calling <code>init()</code> and
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<code>destroy()</code> at the correct times) will be respected.</p>
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</blockquote></td></tr></table>
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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="External Specifications"><strong>External Specifications</strong></a></font></td></tr><tr><td><blockquote>
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<p>I do not know of any formal specification of the behavior of an
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invoker servlet that is publicly available. Anyone know of one?</p>
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</blockquote></td></tr></table>
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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Implementation Requirements"><strong>Implementation Requirements</strong></a></font></td></tr><tr><td><blockquote>
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<p>The implementation of this functionality shall conform to the
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following requirements:</p>
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<ul>
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<li>Implemented as a servlet.</li>
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<li>Exist in the <code>org.apache.catalina.servlets</code> package
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so that it can be loaded by the Catalina class loader.</li>
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<li>Implement the <code>org.apache.catalina.ContainerServlet</code>
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interface, so that it gains knowledge of the <code>Wrapper</code>
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that is responsible for itself and, therefore, access to other
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internal Catalina components.</li>
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<li>Support a configurable debugging detail level.</li>
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<li>Log debugging and operational messages (suitably internationalized)
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via the <code>getServletContext().log()</code> method.</li>
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</ul>
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</blockquote></td></tr></table>
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</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Dependencies"><strong>Dependencies</strong></a></font></td></tr><tr><td><blockquote>
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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Environmental Dependencies"><strong>Environmental Dependencies</strong></a></font></td></tr><tr><td><blockquote>
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<p>The following environmental dependencies must be met in order for
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the Invoker servlet to operate correctly:</p>
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<ul>
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<li>The invoker servlet must be registered in the application deployment
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descriptor (or the default deployment descriptor in file
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<code>$CATALINA_HOME/conf/web.xml</code>) using a "path mapped"
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servlet mapping. The historical default mapping is to URL pattern
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"<code>/servlet/*</code>", although the invoker servlet must operate
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correctly with an arbitrary mapping.</li>
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</ul>
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</blockquote></td></tr></table>
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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Container Dependencies"><strong>Container Dependencies</strong></a></font></td></tr><tr><td><blockquote>
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<p>Correct operation of the invoker servlet depends on the following
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specific features of the surrounding container:</p>
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<ul>
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<li>Correct support for the <code>ContainerServlet</code> interface,
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including calling <code>setWrapper()</code> <strong>before</strong>
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the <code>init()</code> method of the invoker servlet is called.</li>
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<li>The web application class loader must be stored as the context
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class loader of the request processing thread.</li>
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</ul>
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</blockquote></td></tr></table>
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</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Functionality"><strong>Functionality</strong></a></font></td></tr><tr><td><blockquote>
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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Initialization Functionality"><strong>Initialization Functionality</strong></a></font></td></tr><tr><td><blockquote>
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<p>The following processing must be performed when the <code>init()</code>
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method of the invoker servlet is called:</p>
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<ul>
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<li>Ensure that the container has called <code>setWrapper()</code>. If
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not, throw a permanent <code>UnavailableException</code>.</li>
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<li>Look up and cache the <code>Context</code> that corresponds to our
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<code>Wrapper</code>. This is the component with which new servlet
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definitions and mappings will be registered.</li>
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</ul>
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</blockquote></td></tr></table>
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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Per-Request Functionality"><strong>Per-Request Functionality</strong></a></font></td></tr><tr><td><blockquote>
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<p>On each request, the following processing shall be performed:</p>
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<ol>
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<li>Calculate the <code>{ServletPath}</code> for this request, either from
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request attribute <code>javax.servlet.include.servlet_path</code> or
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by calling <code>request.getServletPath()</code>.</li>
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<li>Calculate the <code>{PathInfo}</code> for this request, either from
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request attribute <code>javax.servlet.include.path_info</code> or
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by calling <code>request.getPathInfo()</code>. If the calculated
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<code>{PathInfo}</code> is null, return HTTP status 400
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(bad request).</li>
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<li>Parse the calculated <code>{PathInfo}</code> value as follows:
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<ol>
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<li>Ignore the leading slash character.</li>
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<li>Accumulate characters up to the next '/' (if any) as the
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<code>{ServletSelector}</code>.</li>
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<li>If a '/' was encountered, accumulate all characters from that
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slash (inclusive) to the end of the string as
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<code>{PathRemainder}</code>. If no slash was encountered,
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set <code>{PathRemainder}</code> to a zero-length string.</li>
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</ol></li>
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<li>Determine whether <code>{ServletSelector}</code> is the name of an
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existing servlet definition, and process it as follows:
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<ol>
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<li>Ask our associated <code>Context</code> to find and return a
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child <code>Wrapper</code> named <code>{ServletSelector}</code>.
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</li>
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<li>If there is no such child, skip to the next major step.</li>
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<li>Register a new servlet mapping for this <code>Wrapper</code>,
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using a URL pattern calculated as follows:
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<code>{ServletPath}</code> + "/" + <code>{ServletSelector}</code>
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+ "/*"</li>
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<li>Create a request dispatcher using a path calculated as follows:
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<code>{ServletPath}</code> + "/" + <code>{ServletSelector}</code>
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+ <code>{PathRemainder}</code></li>
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<li>Forward this request to the created request dispatcher, and
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exit from this request.</li>
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</ol></li>
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<li>Assume that <code>{ServletSelector}</code> is the fully qualified
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name of a Java class that implements <code>javax.servlet.Servlet</code>
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and process it as follows:
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<ol>
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<li>Synthesize a new <code>{ServletName}</code> for the servlet
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definition that will be created.</li>
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<li>If there is already a child <code>Wrapper</code> associated with
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this name, return HTTP status 500 (internal server error), because
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a mapping should have already been created for this servlet.</li>
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<li>Attempt to load a class named <code>{ServletSelector}</code> from
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the web application class loader (i.e. the context class loader
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for our current thread). If this fails, return HTTP status 404
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(not found).</li>
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<li>Instantiate an instance of this class. If an error occurs,
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return HTTP status 404 (not found).</li>
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<li>If this class does not implement the
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<code>javax.servlet.Servlet</code> interface, return HTTP status
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404 (not found).</li>
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<li>Create and register a new <code>Wrapper</code> child with our
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<code>Context</code>, under name <code>{ServletName}</code>.</li>
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<li>Register a new servlet mapping for this <code>Wrapper</code>,
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using a URL pattern calculated as follows:
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<code>{ServletPath}</code> + "/" + <code>{ServletSelector}</code>
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+ "/*"</li>
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<li>Create a request dispatcher using a path calculated as follows:
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<code>{ServletPath}</code> + "/" + <code>{ServletSelector}</code>
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+ <code>{PathRemainder}</code></li>
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<li>Forward this request to the created request dispatcher, and
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exit from this request.</li>
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</ol></li>
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</ol>
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</blockquote></td></tr></table>
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<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Finalization Functionality"><strong>Finalization Functionality</strong></a></font></td></tr><tr><td><blockquote>
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<p>No specific processing is required when the <code>destroy()</code>
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method is called:</p>
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</blockquote></td></tr></table>
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</blockquote></td></tr></table><table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Testable Assertions"><strong>Testable Assertions</strong></a></font></td></tr><tr><td><blockquote>
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<p>In addition the the assertions implied by the functionality requirements
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listed above, the following additional assertions shall be tested to
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validate the behavior of the invoker servlet:</p>
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<ul>
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<li>It is possible to access an existing servlet definition by name
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through the invoker. The existing servlet definition can include
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either a <code><servlet-class></code> or
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<code><jsp-file></code> subelement.</li>
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<li>When an existing servlet definition is accessed by name, the request
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will be ultimately processed by the same servlet instance that would
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have processed it had a mapping to that servlet definition been used
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on the request directly.</li>
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<li>It is possible to access an anonymous servlet by class name
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through the invoker.</li>
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<li>When an anonymous servlet is accessed, the servlet instance is processed
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according to the lifecycle requirements of the Servlet Specification.
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</li>
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<li>When an anonymous servlet is accessed, the servlet instance receives
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a <code>ServletConfig</code> instance with no servlet initialization
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parameters.</li>
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<li>It is possible to utilize the invoker servlet via a direct request.</li>
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<li>It is possible to utilize the invoker servlet via a call to
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<code>RequestDispatcher.forward()</code>, or the corresponding
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<code><jsp:forward></code> tag in a JSP page.</li>
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<li>It is possible to utilize the invoker servlet via a call to
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<code>RequestDispatcher.include()</code>, or the corresponding
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<code><jsp:include></code> tag in a JSP page.</li>
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<li>It is possible to use any HTTP method (including GET and POST) that
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is supported by the Servlet class that is ultimately executed.</li>
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<li>The invoker servlet should never be asked to process a second or
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subsequent request for the same <code>{ServletSelector}</code> (because
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it will have registered an appropriate servlet mapping.</li>
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</ul>
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</blockquote></td></tr></table></td></tr><!--FOOTER SEPARATOR--><tr><td colspan="2"><hr noshade="noshade" size="1"></td></tr><!--PAGE FOOTER--><tr><td colspan="2"><div align="center"><font color="#525D76" size="-1"><em>
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Copyright © 1999-2006, Apache Software Foundation
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</em></font></div></td></tr></table></body></html>
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