Valve


1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  
19  package org.apache.catalina;
20  
21  
22  import java.io.IOException  ;
23  import javax.servlet.ServletException  ;
24  
25  import org.apache.catalina.connector.Request;
26  import org.apache.catalina.connector.Response;
27  
28  
29  /**
30   * <p>A <b>Valve</b> is a request processing component associated with a
31   * particular Container.  A series of Valves are generally associated with
32   * each other into a Pipeline.  The detailed contract for a Valve is included
33   * in the description of the <code>invoke()</code> method below.</p>
34   *
35   * <b>HISTORICAL NOTE</b>:  The "Valve" name was assigned to this concept
36   * because a valve is what you use in a real world pipeline to control and/or
37   * modify flows through it.
38   *
39   * @author Craig R. McClanahan
40   * @author Gunnar Rjnning
41   * @author Peter Donald
42   * @version $Revision: 467222 $ $Date: 2006-10-24 05:17:11 +0200 (mar., 24 oct. 2006) $
43   */
44  
45  public interface Valve {
46  
47  
48      //-------------------------------------------------------------- Properties
49  
50  
51      /**
52       * Return descriptive information about this Valve implementation.
53       */
54      public String   getInfo();
55  
56  
57      /**
58       * Return the next Valve in the pipeline containing this Valve, if any.
59       */
60      public Valve getNext();
61  
62  
63      /**
64       * Set the next Valve in the pipeline containing this Valve.
65       *
66       * @param valve The new next valve, or <code>null</code> if none
67       */
68      public void setNext(Valve valve);
69  
70  
71      //---------------------------------------------------------- Public Methods
72  
73  
74      /**
75       * Execute a periodic task, such as reloading, etc. This method will be
76       * invoked inside the classloading context of this container. Unexpected
77       * throwables will be caught and logged.
78       */
79      public void backgroundProcess();
80  
81  
82      /**
83       * <p>Perform request processing as required by this Valve.</p>
84       *
85       * <p>An individual Valve <b>MAY</b> perform the following actions, in
86       * the specified order:</p>
87       * <ul>
88       * <li>Examine and/or modify the properties of the specified Request and
89       *     Response.
90       * <li>Examine the properties of the specified Request, completely generate
91       *     the corresponding Response, and return control to the caller.
92       * <li>Examine the properties of the specified Request and Response, wrap
93       *     either or both of these objects to supplement their functionality,
94       *     and pass them on.
95       * <li>If the corresponding Response was not generated (and control was not
96       *     returned, call the next Valve in the pipeline (if there is one) by
97       *     executing <code>context.invokeNext()</code>.
98       * <li>Examine, but not modify, the properties of the resulting Response
99       *     (which was created by a subsequently invoked Valve or Container).
100      * </ul>
101      *
102      * <p>A Valve <b>MUST NOT</b> do any of the following things:</p>
103      * <ul>
104      * <li>Change request properties that have already been used to direct
105      *     the flow of processing control for this request (for instance,
106      *     trying to change the virtual host to which a Request should be
107      *     sent from a pipeline attached to a Host or Context in the
108      *     standard implementation).
109      * <li>Create a completed Response <strong>AND</strong> pass this
110      *     Request and Response on to the next Valve in the pipeline.
111      * <li>Consume bytes from the input stream associated with the Request,
112      *     unless it is completely generating the response, or wrapping the
113      *     request before passing it on.
114      * <li>Modify the HTTP headers included with the Response after the
115      *     <code>invokeNext()</code> method has returned.
116      * <li>Perform any actions on the output stream associated with the
117      *     specified Response after the <code>invokeNext()</code> method has
118      *     returned.
119      * </ul>
120      *
121      * @param request The servlet request to be processed
122      * @param response The servlet response to be created
123      *
124      * @exception IOException if an input/output error occurs, or is thrown
125      *  by a subsequently invoked Valve, Filter, or Servlet
126      * @exception ServletException if a servlet error occurs, or is thrown
127      *  by a subsequently invoked Valve, Filter, or Servlet
128      */
129     public void invoke(Request request, Response response)
130         throws IOException  , ServletException  ;
131 
132     
133     /**
134      * Process a Comet event.
135      *
136      * @param request The servlet request to be processed
137      * @param response The servlet response to be created
138      *
139      * @exception IOException if an input/output error occurs, or is thrown
140      *  by a subsequently invoked Valve, Filter, or Servlet
141      * @exception ServletException if a servlet error occurs, or is thrown
142      *  by a subsequently invoked Valve, Filter, or Servlet
143      */
144     public void event(Request request, Response response, CometEvent event)
145         throws IOException  , ServletException  ;
146 
147 
148 }
149
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