001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017 package org.apache.commons.chain.web.servlet;
018
019
020 import java.io.IOException;
021 import javax.servlet.ServletException;
022 import javax.servlet.http.HttpServletRequest;
023 import javax.servlet.http.HttpServletResponse;
024 import org.apache.commons.chain.Catalog;
025 import org.apache.commons.chain.CatalogFactory;
026 import org.apache.commons.chain.Command;
027 import org.apache.commons.chain.web.ChainServlet;
028
029
030 /**
031 * <p>Custom subclass of {@link ChainServlet} that also dispatches incoming
032 * requests to a configurable {@link Command} loaded from the specified
033 * {@link Catalog}.</p>
034 *
035 * <p>In addition to the <em>servlet</em> init parameters supported by
036 * {@link ChainServlet}, this class supports the following additional
037 * parameters:</p>
038 * <ul>
039 * <li><strong>org.apache.commons.chain.CATALOG</strong> - Name of the
040 * catalog from which to acquire commands to be executed. If not
041 * specified, the default catalog for this application will be used.</li>
042 * <li><strong>org.apache.commons.chain.COMMAND</strong> - Name of the
043 * {@link Command} (looked up in our configured {@link Catalog} used
044 * to process all incoming servlet requests. If not specified,
045 * defaults to <code>command</code>.</li>
046 * </ul>
047 *
048 * <p>Also, the <code>org.apache.commons.chain.CONFIG_ATTR</code>
049 * init parameter is also used to identify the
050 * {@link org.apache.commons.chain.Context} attribute under
051 * which our configured {@link Catalog} will be made available to
052 * {@link Command}s processing our requests, in addition to its definition
053 * of the <code>ServletContext</code> attribute key under which the
054 * {@link Catalog} is available.</p>
055 */
056
057 public class ChainProcessor extends ChainServlet {
058
059
060 // ------------------------------------------------------ Manifest Constants
061
062
063 /**
064 * <p>The name of the servlet init parameter containing the name of the
065 * {@link Catalog} to use for processing incoming requests.</p>
066 */
067 public static final String CATALOG =
068 "org.apache.commons.chain.CATALOG";
069
070
071 /**
072 * <p>The default request attribute under which we expose the
073 * {@link Catalog} being used to subordinate {@link Command}s.</p>
074 */
075 public static final String CATALOG_DEFAULT =
076 "org.apache.commons.chain.CATALOG";
077
078
079 /**
080 * <p>The name of the servlet init parameter containing the name of the
081 * {@link Command} (loaded from our configured {@link Catalog} to use
082 * for processing each incoming request.</p>
083 */
084 public static final String COMMAND =
085 "org.apache.commons.chain.COMMAND";
086
087
088 /**
089 * <p>The default command name.</p>
090 */
091 private static final String COMMAND_DEFAULT = "command";
092
093
094 // ------------------------------------------------------ Instance Variables
095
096
097 /**
098 * <p>The name of the context attribute under which our {@link Catalog}
099 * is stored. This value is also used as the name of the
100 * context attribute under which the catalog is exposed to commands.
101 * If not specified, we will look up commands in the appropriate
102 * {@link Catalog} retrieved from our {@link CatalogFactory}.</p>
103 */
104 private String attribute = null;
105
106
107 /**
108 * <p>The name of the {@link Catalog} to retrieve from the
109 * {@link CatalogFactory} for this application, or <code>null</code>
110 * to select the default {@link Catalog}.</p>
111 */
112 private String catalog = null;
113
114
115 /**
116 * <p>The name of the {@link Command} to be executed for each incoming
117 * request.</p>
118 */
119 private String command = null;
120
121
122 // --------------------------------------------------------- Servlet Methods
123
124
125 /**
126 * <p>Clean up as this application is shut down.</p>
127 */
128 public void destroy() {
129
130 super.destroy();
131 attribute = null;
132 catalog = null;
133 command = null;
134
135 }
136
137
138 /**
139 * <p>Cache the name of the command we should execute for each request.</p>
140 *
141 * @exception ServletException if an initialization error occurs
142 */
143 public void init() throws ServletException {
144
145 super.init();
146 attribute = getServletConfig().getInitParameter(CONFIG_ATTR);
147 catalog = getServletConfig().getInitParameter(CATALOG);
148 command = getServletConfig().getInitParameter(COMMAND);
149 if (command == null) {
150 command = COMMAND_DEFAULT;
151 }
152
153 }
154
155
156 /**
157 * <p>Configure a {@link ServletWebContext} for the current request, and
158 * pass it to the <code>execute()</code> method of the specified
159 * {@link Command}, loaded from our configured {@link Catalog}.</p>
160 *
161 * @param request The request we are processing
162 * @param response The response we are creating
163 *
164 * @exception IOException if an input/output error occurs
165 * @exception ServletException if a servlet exception occurs
166 */
167 public void service(HttpServletRequest request,
168 HttpServletResponse response)
169 throws IOException, ServletException {
170
171 ServletWebContext context =
172 new ServletWebContext(getServletContext(), request, response);
173 Catalog theCatalog = null;
174 if (attribute != null) {
175 theCatalog = (Catalog) getServletContext().getAttribute
176 (this.attribute);
177 } else if (catalog != null) {
178 theCatalog = CatalogFactory.getInstance().getCatalog(catalog);
179 } else {
180 theCatalog = CatalogFactory.getInstance().getCatalog();
181 }
182 if (attribute == null) {
183 request.setAttribute(CATALOG_DEFAULT, theCatalog);
184 }
185 Command command = theCatalog.getCommand(this.command);
186 try {
187 command.execute(context);
188 } catch (Exception e) {
189 throw new ServletException(e);
190 }
191
192 }
193
194
195 }