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Java > Open Source Codes > org > apache > turbine > Valve


1 package org.apache.turbine;
2
3 /* ====================================================================
4  * The Apache Software License, Version 1.1
5  *
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10  * modification, are permitted provided that the following conditions
11  * are met:
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14  * notice, this list of conditions and the following disclaimer.
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17  * notice, this list of conditions and the following disclaimer in
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19  * distribution.
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21  * 3. The end-user documentation included with the redistribution,
22  * if any, must include the following acknowledgment:
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24  * Apache Software Foundation (http://www.apache.org/)."
25  * Alternately, this acknowledgment may appear in the software itself,
26  * if and wherever such third-party acknowledgments normally appear.
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28  * 4. The names "Apache" and "Apache Software Foundation" and
29  * "Apache Turbine" must not be used to endorse or promote products
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31  * written permission, please contact apache@apache.org.
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34  * "Apache Turbine", nor may "Apache" appear in their name, without
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51  * This software consists of voluntary contributions made by many
52  * individuals on behalf of the Apache Software Foundation. For more
53  * information on the Apache Software Foundation, please see
54  * <http://www.apache.org/>.
55  */
56
57 import java.io.IOException JavaDoc;
58
59 /**
60  * <p>A <b>Valve</b> is a request processing component. A series of
61  * Valves are generally associated with each other into a Pipeline.
62  * The detailed contract for a Valve is included in the description of
63  * the <code>invoke()</code> method below.</p>
64  *
65  * <b>HISTORICAL NOTE</b>: The "Valve" name was assigned to this concept
66  * because a valve is what you use in a real world pipeline to control and/or
67  * modify flows through it.
68  *
69  * @author Craig R. McClanahan
70  * @author Gunnar Rjnning
71  * @author Peter Donald
72  * @author <a HREF="mailto:dlr@finemaltcoding.com">Daniel Rall</a>
73  *
74  * @see #invoke(RunData, ValveContext)
75  */
76 public interface Valve
77 {
78     /**
79      * <p>Perform request processing as required by this Valve.</p>
80      *
81      * <p>An individual Valve <b>MAY</b> perform the following actions, in
82      * the specified order:</p>
83      * <ul>
84      * <li>Examine and/or modify the properties of the specified Request and
85      * Response.
86      * <li>Examine the properties of the specified Request, completely generate
87      * the corresponding Response, and return control to the caller.
88      * <li>Examine the properties of the specified Request and Response, wrap
89      * either or both of these objects to supplement their functionality,
90      * and pass them on.
91      * <li>If the corresponding Response was not generated (and control was not
92      * returned, call the next Valve in the pipeline (if there is one) by
93      * executing <code>context.invokeNext()</code>.
94      * <li>Examine, but not modify, the properties of the resulting Response
95      * (which was created by a subsequently invoked Valve via a
96      * call to <code>context.invokeNext()</code>).
97      * </ul>
98      *
99      * <p>A Valve <b>MUST NOT</b> do any of the following things:</p>
100      * <ul>
101      * <li>Change request properties that have already been used to direct
102      * the flow of processing control for this request.
103      * <li>Create a completed Response <strong>AND</strong> pass this
104      * Request and Response on to the next Valve in the pipeline.
105      * <li>Consume bytes from the input stream associated with the Request,
106      * unless it is completely generating the response, or wrapping the
107      * request before passing it on.
108      * <li>Modify the HTTP headers included with the Response after the
109      * <code>invokeNext()</code> method has returned.
110      * <li>Perform any actions on the output stream associated with the
111      * specified Response after the <code>invokeNext()</code> method has
112      * returned.
113      * </ul>
114      *
115      * @param data The run-time information, including the servlet
116      * request and response we are processing.
117      * @param context The valve context used to invoke the next valve
118      * in the current processing pipeline
119      *
120      * @exception IOException Thrown by a subsequent Valve.
121      * @exception TurbineException Thrown by a subsequent Valve.
122      */
123     public void invoke(RunData data, ValveContext context)
124         throws IOException JavaDoc, TurbineException;
125
126     /**
127      * Initialize the valve before using in a pipeline.
128      */
129     public void initialize()
130         throws Exception JavaDoc;
131 }
132
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