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1<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>Catalina Functional Specifications - Invoker Servlet</title><meta value="Craig McClanahan" name="author"><meta value="craigmcc@apache.org" name="email"></head><body vlink="#525D76" alink="#525D76" link="#525D76" text="#000000" bgcolor="#ffffff"><table cellspacing="0" width="100%" border="0"><!--PAGE HEADER--><tr><td><!--PROJECT LOGO--><a href="http://tomcat.apache.org/"><img border="0" alt="
2      Catalina Functional Specifications
3    " align="right" src="../../../images/tomcat.gif"></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 border="0" alt="Apache Logo" align="right" src="../../../images/asf-logo.gif"></a></td></tr></table><table cellspacing="4" width="100%" border="0"><!--HEADER SEPARATOR--><tr><td colspan="2"><hr size="1" noshade></td></tr><tr><!--RIGHT SIDE MAIN BODY--><td align="left" valign="top" width="80%"><table cellspacing="4" width="100%" border="0"><tr><td valign="top" align="left"><h1>Catalina Functional Specifications</h1><h2>Invoker Servlet</h2></td><td nowrap="true" valign="top" align="right"><img border="0" hspace="0" vspace="0" height="1" width="1" src="../../../images/void.gif"></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Overview"><strong>Overview</strong></a></font></td></tr><tr><td><blockquote>
4
5
6  <table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#828DA6"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Introduction"><strong>Introduction</strong></a></font></td></tr><tr><td><blockquote>
7
8    <p>The purpose of the <strong>Invoker Servlet</strong> is to allow a
9    web application to dynamically register new <em>servlet definitions</em>
10    that correspond with a <code>&lt;servlet&gt;</code> element in the
11    <code>/WEB-INF/web.xml</code> deployment descriptor, and execute
12    requests utilizing the new servlet definitions.  From the perspective
13    of the newly registered servlets, all servlet lifecycle requirements
14    of the Servlet Specification (such as calling <code>init()</code> and
15    <code>destroy()</code> at the correct times) will be respected.</p>
16
17  </blockquote></td></tr></table>
18
19
20  <table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#828DA6"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="External Specifications"><strong>External Specifications</strong></a></font></td></tr><tr><td><blockquote>
21
22    <p>I do not know of any formal specification of the behavior of an
23    invoker servlet that is publicly available.  Anyone know of one?</p>
24
25  </blockquote></td></tr></table>
26
27
28  <table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#828DA6"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Implementation Requirements"><strong>Implementation Requirements</strong></a></font></td></tr><tr><td><blockquote>
29
30    <p>The implementation of this functionality shall conform to the
31    following requirements:</p>
32    <ul>
33    <li>Implemented as a servlet.</li>
34    <li>Exist in the <code>org.apache.catalina.servlets</code> package
35        so that it can be loaded by the Catalina class loader.</li>
36    <li>Implement the <code>org.apache.catalina.ContainerServlet</code>
37        interface, so that it gains knowledge of the <code>Wrapper</code>
38        that is responsible for itself and, therefore, access to other
39        internal Catalina components.</li>
40    <li>Support a configurable debugging detail level.</li>
41    <li>Log debugging and operational messages (suitably internationalized)
42        via the <code>getServletContext().log()</code> method.</li>
43    </ul>
44
45  </blockquote></td></tr></table>
46
47
48</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Dependencies"><strong>Dependencies</strong></a></font></td></tr><tr><td><blockquote>
49
50
51  <table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#828DA6"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Environmental Dependencies"><strong>Environmental Dependencies</strong></a></font></td></tr><tr><td><blockquote>
52
53    <p>The following environmental dependencies must be met in order for
54    the Invoker servlet to operate correctly:</p>
55    <ul>
56    <li>The invoker servlet must be registered in the application deployment
57        descriptor (or the default deployment descriptor in file
58        <code>$CATALINA_BASE/conf/web.xml</code>) using a "path mapped"
59        servlet mapping.  The historical default mapping is to URL pattern
60        "<code>/servlet/*</code>", although the invoker servlet must operate
61        correctly with an arbitrary mapping.</li>
62    </ul>
63
64  </blockquote></td></tr></table>
65
66
67  <table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#828DA6"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Container Dependencies"><strong>Container Dependencies</strong></a></font></td></tr><tr><td><blockquote>
68
69    <p>Correct operation of the invoker servlet depends on the following
70    specific features of the surrounding container:</p>
71    <ul>
72    <li>Correct support for the <code>ContainerServlet</code> interface,
73        including calling <code>setWrapper()</code> <strong>before</strong>
74        the <code>init()</code> method of the invoker servlet is called.</li>
75    <li>The web application class loader must be stored as the context
76        class loader of the request processing thread.</li>
77    </ul>
78
79  </blockquote></td></tr></table>
80
81
82</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Functionality"><strong>Functionality</strong></a></font></td></tr><tr><td><blockquote>
83
84
85  <table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#828DA6"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Initialization Functionality"><strong>Initialization Functionality</strong></a></font></td></tr><tr><td><blockquote>
86
87    <p>The following processing must be performed when the <code>init()</code>
88    method of the invoker servlet is called:</p>
89    <ul>
90    <li>Ensure that the container has called <code>setWrapper()</code>.  If
91        not, throw a permanent <code>UnavailableException</code>.</li>
92    <li>Look up and cache the <code>Context</code> that corresponds to our
93        <code>Wrapper</code>.  This is the component with which new servlet
94        definitions and mappings will be registered.</li>
95    </ul>
96
97  </blockquote></td></tr></table>
98
99
100  <table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#828DA6"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Per-Request Functionality"><strong>Per-Request Functionality</strong></a></font></td></tr><tr><td><blockquote>
101
102    <p>On each request, the following processing shall be performed:</p>
103    <ol>
104    <li>Calculate the <code>{ServletPath}</code> for this request, either from
105        request attribute <code>javax.servlet.include.servlet_path</code> or
106        by calling <code>request.getServletPath()</code>.</li>
107    <li>Calculate the <code>{PathInfo}</code> for this request, either from
108        request attribute <code>javax.servlet.include.path_info</code> or
109        by calling <code>request.getPathInfo()</code>.  If the calculated
110        <code>{PathInfo}</code> is null, return HTTP status 400
111        (bad request).</li>
112    <li>Parse the calculated <code>{PathInfo}</code> value as follows:
113        <ol>
114        <li>Ignore the leading slash character.</li>
115        <li>Accumulate characters up to the next '/' (if any) as the
116            <code>{ServletSelector}</code>.</li>
117        <li>If a '/' was encountered, accumulate all characters from that
118            slash (inclusive) to the end of the string as
119            <code>{PathRemainder}</code>.  If no slash was encountered,
120            set <code>{PathRemainder}</code> to a zero-length string.</li>
121        </ol></li>
122    <li>Determine whether <code>{ServletSelector}</code> is the name of an
123        existing servlet definition, and process it as follows:
124        <ol>
125        <li>Ask our associated <code>Context</code> to find and return a
126            child <code>Wrapper</code> named <code>{ServletSelector}</code>.
127            </li>
128        <li>If there is no such child, skip to the next major step.</li>
129        <li>Register a new servlet mapping for this <code>Wrapper</code>,
130            using a URL pattern calculated as follows:
131            <code>{ServletPath}</code> + "/" + <code>{ServletSelector}</code>
132            + "/*"</li>
133        <li>Create a request dispatcher using a path calculated as follows:
134            <code>{ServletPath}</code> + "/" + <code>{ServletSelector}</code>
135            + <code>{PathRemainder}</code></li>
136        <li>Forward this request to the created request dispatcher, and
137            exit from this request.</li>
138        </ol></li>
139    <li>Assume that <code>{ServletSelector}</code> is the fully qualified
140        name of a Java class that implements <code>javax.servlet.Servlet</code>
141        and process it as follows:
142        <ol>
143        <li>Synthesize a new <code>{ServletName}</code> for the servlet
144            definition that will be created.</li>
145        <li>If there is already a child <code>Wrapper</code> associated with
146            this name, return HTTP status 500 (internal server error), because
147            a mapping should have already been created for this servlet.</li>
148        <li>Attempt to load a class named <code>{ServletSelector}</code> from
149            the web application class loader (i.e. the context class loader
150            for our current thread).  If this fails, return HTTP status 404
151            (not found).</li>
152        <li>Instantiate an instance of this class.  If an error occurs,
153            return HTTP status 404 (not found).</li>
154        <li>If this class does not implement the
155            <code>javax.servlet.Servlet</code> interface, return HTTP status
156            404 (not found).</li>
157        <li>Create and register a new <code>Wrapper</code> child with our
158            <code>Context</code>, under name <code>{ServletName}</code>.</li>
159        <li>Register a new servlet mapping for this <code>Wrapper</code>,
160            using a URL pattern calculated as follows:
161            <code>{ServletPath}</code> + "/" + <code>{ServletSelector}</code>
162            + "/*"</li>
163        <li>Create a request dispatcher using a path calculated as follows:
164            <code>{ServletPath}</code> + "/" + <code>{ServletSelector}</code>
165            + <code>{PathRemainder}</code></li>
166        <li>Forward this request to the created request dispatcher, and
167            exit from this request.</li>
168        </ol></li>
169    </ol>
170
171  </blockquote></td></tr></table>
172
173
174  <table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#828DA6"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Finalization Functionality"><strong>Finalization Functionality</strong></a></font></td></tr><tr><td><blockquote>
175
176    <p>No specific processing is required when the <code>destroy()</code>
177    method is called:</p>
178
179  </blockquote></td></tr></table>
180
181
182</blockquote></td></tr></table><table cellpadding="2" cellspacing="0" border="0"><tr><td bgcolor="#525D76"><font face="arial,helvetica.sanserif" color="#ffffff"><a name="Testable Assertions"><strong>Testable Assertions</strong></a></font></td></tr><tr><td><blockquote>
183
184  <p>In addition the the assertions implied by the functionality requirements
185  listed above, the following additional assertions shall be tested to
186  validate the behavior of the invoker servlet:</p>
187  <ul>
188  <li>It is possible to access an existing servlet definition by name
189      through the invoker.  The existing servlet definition can include
190      either a <code>&lt;servlet-class&gt;</code> or
191      <code>&lt;jsp-file&gt;</code> subelement.</li>
192  <li>When an existing servlet definition is accessed by name, the request
193      will be ultimately processed by the same servlet instance that would
194      have processed it had a mapping to that servlet definition been used
195      on the request directly.</li>
196  <li>It is possible to access an anonymous servlet by class name
197      through the invoker.</li>
198  <li>When an anonymous servlet is accessed, the servlet instance is processed
199      according to the lifecycle requirements of the Servlet Specification.
200      </li>
201  <li>When an anonymous servlet is accessed, the servlet instance receives
202      a <code>ServletConfig</code> instance with no servlet initialization
203      parameters.</li>
204  <li>It is possible to utilize the invoker servlet via a direct request.</li>
205  <li>It is possible to utilize the invoker servlet via a call to
206      <code>RequestDispatcher.forward()</code>, or the corresponding
207      <code>&lt;jsp:forward&gt;</code> tag in a JSP page.</li>
208  <li>It is possible to utilize the invoker servlet via a call to
209      <code>RequestDispatcher.include()</code>, or the corresponding
210      <code>&lt;jsp:include&gt;</code> tag in a JSP page.</li>
211  <li>It is possible to use any HTTP method (including GET and POST) that
212      is supported by the Servlet class that is ultimately executed.</li>
213  <li>The invoker servlet should never be asked to process a second or
214      subsequent request for the same <code>{ServletSelector}</code> (because
215      it will have registered an appropriate servlet mapping.</li>
216  </ul>
217
218</blockquote></td></tr></table></td></tr><!--FOOTER SEPARATOR--><tr><td colspan="2"><hr size="1" noshade></td></tr><!--PAGE FOOTER--><tr><td colspan="2"><div align="center"><font size="-1" color="#525D76"><em>
219        Copyright &copy; 1999-2008, Apache Software Foundation
220        </em></font></div></td></tr></table></body></html>
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