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;
018
019 import java.util.HashMap;
020 import java.util.Iterator;
021 import java.util.Map;
022 import org.apache.commons.chain.impl.CatalogFactoryBase;
023
024 import org.apache.commons.logging.Log;
025 import org.apache.commons.logging.LogFactory;
026
027 /**
028 * <p>A {@link CatalogFactory} is a class used to store and retrieve
029 * {@link Catalog}s. The factory allows for a default {@link Catalog}
030 * as well as {@link Catalog}s stored with a name key. Follows the
031 * Factory pattern (see GoF).</p>
032 *
033 * <p>The base <code>CatalogFactory</code> implementation also implements
034 * a resolution mechanism which allows lookup of a command based on a single
035 * String which encodes both the catalog and command names.</p>
036 *
037 * @author Sean Schofield
038 * @version $Revision: 480477 $ $Date: 2006-11-29 08:34:52 +0000 (Wed, 29 Nov 2006) $
039 */
040
041 public abstract class CatalogFactory {
042
043
044 /**
045 * <p>Values passed to the <code>getCommand(String)</code> method should
046 * use this as the delimiter between the "catalog" name and the "command"
047 * name.</p>
048 */
049 public static final String DELIMITER = ":";
050
051
052 // --------------------------------------------------------- Public Methods
053
054
055 /**
056 * <p>Gets the default instance of Catalog associated with the factory
057 * (if any); otherwise, return <code>null</code>.</p>
058 *
059 * @return the default Catalog instance
060 */
061 public abstract Catalog getCatalog();
062
063
064 /**
065 * <p>Sets the default instance of Catalog associated with the factory.</p>
066 *
067 * @param catalog the default Catalog instance
068 */
069 public abstract void setCatalog(Catalog catalog);
070
071
072 /**
073 * <p>Retrieves a Catalog instance by name (if any); otherwise
074 * return <code>null</code>.</p>
075 *
076 * @param name the name of the Catalog to retrieve
077 * @return the specified Catalog
078 */
079 public abstract Catalog getCatalog(String name);
080
081
082 /**
083 * <p>Adds a named instance of Catalog to the factory (for subsequent
084 * retrieval later).</p>
085 *
086 * @param name the name of the Catalog to add
087 * @param catalog the Catalog to add
088 */
089 public abstract void addCatalog(String name, Catalog catalog);
090
091
092 /**
093 * <p>Return an <code>Iterator</code> over the set of named
094 * {@link Catalog}s known to this {@link CatalogFactory}.
095 * If there are no known catalogs, an empty Iterator is returned.</p>
096 * @return An Iterator of the names of the Catalogs known by this factory.
097 */
098 public abstract Iterator getNames();
099
100
101 /**
102 * <p>Return a <code>Command</code> based on the given commandID.</p>
103 *
104 * <p>At this time, the structure of commandID is relatively simple: if the
105 * commandID contains a DELIMITER, treat the segment of the commandID
106 * up to (but not including) the DELIMITER as the name of a catalog, and the
107 * segment following the DELIMITER as a command name within that catalog.
108 * If the commandID contains no DELIMITER, treat the commandID as the name
109 * of a command in the default catalog.</p>
110 *
111 * <p>To preserve the possibility of future extensions to this lookup
112 * mechanism, the DELIMITER string should be considered reserved, and
113 * should not be used in command names. commandID values which contain
114 * more than one DELIMITER will cause an
115 * <code>IllegalArgumentException</code> to be thrown.</p>
116 *
117 * @param commandID the identifier of the command to return
118 * @return the command located with commandID, or <code>null</code>
119 * if either the command name or the catalog name cannot be resolved
120 * @throws IllegalArgumentException if the commandID contains more than
121 * one DELIMITER
122 *
123 * @since Chain 1.1
124 */
125 public Command getCommand(String commandID) {
126
127 String commandName = commandID;
128 String catalogName = null;
129 Catalog catalog = null;
130
131 if (commandID != null) {
132 int splitPos = commandID.indexOf(DELIMITER);
133 if (splitPos != -1) {
134 catalogName = commandID.substring(0, splitPos);
135 commandName = commandID.substring(splitPos + DELIMITER.length());
136 if (commandName.indexOf(DELIMITER) != -1) {
137 throw new IllegalArgumentException("commandID [" +
138 commandID +
139 "] has too many delimiters (reserved for future use)");
140 }
141 }
142 }
143
144 if (catalogName != null) {
145 catalog = this.getCatalog(catalogName);
146 if (catalog == null) {
147 Log log = LogFactory.getLog(CatalogFactory.class);
148 log.warn("No catalog found for name: " + catalogName + ".");
149 return null;
150 }
151 } else {
152 catalog = this.getCatalog();
153 if (catalog == null) {
154 Log log = LogFactory.getLog(CatalogFactory.class);
155 log.warn("No default catalog found.");
156 return null;
157 }
158 }
159
160 return catalog.getCommand(commandName);
161
162 }
163
164
165 // ------------------------------------------------------- Static Variables
166
167
168 /**
169 * <p>The set of registered {@link CatalogFactory} instances,
170 * keyed by the relevant class loader.</p>
171 */
172 private static Map factories = new HashMap();
173
174
175 // -------------------------------------------------------- Static Methods
176
177
178 /**
179 * <p>Return the singleton {@link CatalogFactory} instance
180 * for the relevant <code>ClassLoader</code>. For applications
181 * that use a thread context class loader (such as web applications
182 * running inside a servet container), this will return a separate
183 * instance for each application, even if this class is loaded from
184 * a shared parent class loader.</p>
185 *
186 * @return the per-application singleton instance of {@link CatalogFactory}
187 */
188 public static CatalogFactory getInstance() {
189
190 CatalogFactory factory = null;
191 ClassLoader cl = getClassLoader();
192 synchronized (factories) {
193 factory = (CatalogFactory) factories.get(cl);
194 if (factory == null) {
195 factory = new CatalogFactoryBase();
196 factories.put(cl, factory);
197 }
198 }
199 return factory;
200
201 }
202
203
204 /**
205 * <p>Clear all references to registered catalogs, as well as to the
206 * relevant class loader. This method should be called, for example,
207 * when a web application utilizing this class is removed from
208 * service, to allow for garbage collection.</p>
209 */
210 public static void clear() {
211
212 synchronized (factories) {
213 factories.remove(getClassLoader());
214 }
215
216 }
217
218
219 // ------------------------------------------------------- Private Methods
220
221
222 /**
223 * <p>Return the relevant <code>ClassLoader</code> to use as a Map key
224 * for this request. If there is a thread context class loader, return
225 * that; otherwise, return the class loader that loaded this class.</p>
226 */
227 private static ClassLoader getClassLoader() {
228
229 ClassLoader cl = Thread.currentThread().getContextClassLoader();
230 if (cl == null) {
231 cl = CatalogFactory.class.getClassLoader();
232 }
233 return cl;
234
235 }
236
237 }