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Java > Open Source Codes > org > apache > commons > chain > web > servlet > ChainProcessor


1 /*
2  * Copyright 1999-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.chain.web.servlet;
17
18
19 import java.io.IOException JavaDoc;
20 import javax.servlet.ServletException JavaDoc;
21 import javax.servlet.http.HttpServletRequest JavaDoc;
22 import javax.servlet.http.HttpServletResponse JavaDoc;
23 import org.apache.commons.chain.Catalog;
24 import org.apache.commons.chain.CatalogFactory;
25 import org.apache.commons.chain.Command;
26 import org.apache.commons.chain.web.ChainServlet;
27
28
29 /**
30  * <p>Custom subclass of {@link ChainServlet} that also dispatches incoming
31  * requests to a configurable {@link Command} loaded from the specified
32  * {@link Catalog}.</p>
33  *
34  * <p>In addition to the <em>servlet</em> init parameters supported by
35  * {@link ChainServlet}, this class supports the following additional
36  * parameters:</p>
37  * <ul>
38  * <li><strong>org.apache.commons.chain.CATALOG</strong> - Name of the
39  * catalog from which to acquire commands to be executed. If not
40  * specified, the default catalog for this application will be used.</li>
41  * <li><strong>org.apache.commons.chain.COMMAND</strong> - Name of the
42  * {@link Command} (looked up in our configured {@link Catalog} used
43  * to process all incoming servlet requests. If not specified,
44  * defaults to <code>command</code>.</li>
45  * </ul>
46  *
47  * <p>Also, the <code>org.apache.commons.chain.CONFIG_ATTR</code>
48  * init parameter is also used to identify the {@link Context} attribute under
49  * which our configured {@link Catalog} will be made available to
50  * {@link Command}s processing our requests, in addition to its definition
51  * of the <code>ServletContext</code> attribute key under which the
52  * {@link Catalog} is available.</p>
53  */
54
55 public class ChainProcessor extends ChainServlet {
56
57
58     // ------------------------------------------------------ Manifest Constants
59
60
61     /**
62      * <p>The name of the servlet init parameter containing the name of the
63      * {@link Catalog} to use for processing incoming requests.</p>
64      */
65     public static final String JavaDoc CATALOG =
66         "org.apache.commons.chain.CATALOG";
67
68
69     /**
70      * <p>The default request attribute under which we expose the
71      * {@link Catalog} being used to subordinate {@link Command}s.</p>
72      */
73     public static final String JavaDoc CATALOG_DEFAULT =
74         "org.apache.commons.chain.CATALOG";
75
76
77     /**
78      * <p>The name of the servlet init parameter containing the name of the
79      * {@link Command} (loaded from our configured {@link Catalog} to use
80      * for processing each incoming request.</p>
81      */
82     public static final String JavaDoc COMMAND =
83         "org.apache.commons.chain.COMMAND";
84
85
86     /**
87      * <p>The default command name.</p>
88      */
89     private static final String JavaDoc COMMAND_DEFAULT = "command";
90
91
92     // ------------------------------------------------------ Instance Variables
93
94
95     /**
96      * <p>The name of the context attribute under which our {@link Catalog}
97      * is stored. This value is also used as the name of the
98      * context attribute under which the catalog is exposed to commands.
99      * If not specified, we will look up commands in the appropriate
100      * {@link Catalog} retrieved from our {@link CatalogFactory}.</p>
101      */
102     private String JavaDoc attribute = null;
103
104
105     /**
106      * <p>The name of the {@link Catalog} to retrieve from the
107      * {@link CatalogFactory} for this application, or <code>null</code>
108      * to select the default {@link Catalog}.</p>
109      */
110     private String JavaDoc catalog = null;
111
112
113     /**
114      * <p>The name of the {@link Command} to be executed for each incoming
115      * request.</p>
116      */
117     private String JavaDoc command = null;
118
119
120     /**
121      * <p>The {@link CatalogFactory} for this application.</p>
122      */
123     private CatalogFactory factory = null;
124
125
126     // --------------------------------------------------------- Servlet Methods
127
128
129     /**
130      * <p>Clean up as this application is shut down.</p>
131      */
132     public void destroy() {
133
134         super.destroy();
135         attribute = null;
136         catalog = null;
137         command = null;
138         factory = null;
139
140     }
141
142
143     /**
144      * <p>Cache the name of the command we should execute for each request.</p>
145      *
146      * @exception ServletException if an initialization error occurs
147      */
148     public void init() throws ServletException JavaDoc {
149
150         super.init();
151         attribute = getServletConfig().getInitParameter(CONFIG_ATTR);
152         catalog = getServletConfig().getInitParameter(CATALOG);
153         command = getServletConfig().getInitParameter(COMMAND);
154         if (command == null) {
155             command = COMMAND_DEFAULT;
156         }
157         factory = CatalogFactory.getInstance();
158
159     }
160
161
162     /**
163      * <p>Configure a {@link ServletWebContext} for the current request, and
164      * pass it to the <code>execute()</code> method of the specified
165      * {@link Command}, loaded from our configured {@link Catalog}.</p>
166      *
167      * @param request The request we are processing
168      * @param response The response we are creating
169      *
170      * @exception IOException if an input/output error occurs
171      * @exception ServletException if a servlet exception occurs
172      */
173     public void service(HttpServletRequest JavaDoc request,
174                         HttpServletResponse JavaDoc response)
175         throws IOException JavaDoc, ServletException JavaDoc {
176
177         ServletWebContext context =
178             new ServletWebContext(getServletContext(), request, response);
179         Catalog theCatalog = null;
180         if (attribute != null) {
181             theCatalog = (Catalog) getServletContext().getAttribute
182                 (this.attribute);
183         } else if (catalog != null) {
184             theCatalog = factory.getCatalog(catalog);
185         } else {
186             theCatalog = factory.getCatalog();
187         }
188         if (attribute == null) {
189             request.setAttribute(CATALOG_DEFAULT, theCatalog);
190         }
191         Command command = theCatalog.getCommand(this.command);
192         try {
193             command.execute(context);
194         } catch (Exception JavaDoc e) {
195             throw new ServletException JavaDoc(e);
196         }
197
198     }
199
200
201 }
202
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