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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;
20  import javax.servlet.ServletException;
21  import javax.servlet.http.HttpServletRequest;
22  import javax.servlet.http.HttpServletResponse;
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 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 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 COMMAND =
83          "org.apache.commons.chain.COMMAND";
84  
85  
86      /***
87       * <p>The default command name.</p>
88       */
89      private static final String 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 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 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 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 {
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 request,
174                         HttpServletResponse response)
175         throws IOException, ServletException {
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 e) {
195             throw new ServletException(e);
196         }
197 
198     }
199 
200 
201 }