001    /* $Id: FinderFromDfltClass.java 729125 2008-12-23 21:21:07Z rahul $
002     *
003     * Licensed to the Apache Software Foundation (ASF) under one or more
004     * contributor license agreements.  See the NOTICE file distributed with
005     * this work for additional information regarding copyright ownership.
006     * The ASF licenses this file to You under the Apache License, Version 2.0
007     * (the "License"); you may not use this file except in compliance with
008     * the License.  You may obtain a copy of the License at
009     * 
010     *      http://www.apache.org/licenses/LICENSE-2.0
011     * 
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */ 
018     
019    package org.apache.commons.digester.plugins.strategies;
020    
021    import java.util.Properties;
022    import org.apache.commons.digester.Digester;
023    import org.apache.commons.digester.plugins.RuleFinder;
024    import org.apache.commons.digester.plugins.RuleLoader;
025    import org.apache.commons.digester.plugins.PluginException;
026    
027    /**
028     * A rule-finding algorithm which looks for a method with a specific name
029     * on a class whose name is derived from the plugin class name.
030     *
031     * @since 1.6
032     */
033    
034    public class FinderFromDfltClass extends RuleFinder {
035        public static String DFLT_RULECLASS_SUFFIX = "RuleInfo";
036        public static String DFLT_METHOD_NAME = "addRules";
037        
038        private String rulesClassSuffix;
039        private String methodName;
040        
041        /** See {@link #findLoader}. */
042        public FinderFromDfltClass() {
043            this(DFLT_RULECLASS_SUFFIX, DFLT_METHOD_NAME);
044        }
045        
046        /**
047         * Create a rule-finder which invokes a method on a class whenever 
048         * dynamic rules for a plugin need to be loaded. See the findRules 
049         * method for more info.
050         *
051         * @param rulesClassSuffix must be non-null.
052         * @param methodName may be null.
053         */
054         public FinderFromDfltClass(String rulesClassSuffix, String methodName) { 
055            this.rulesClassSuffix = rulesClassSuffix;
056            this.methodName = methodName;
057        }
058        
059        /**
060         * If there exists a class whose name is the plugin class name + the
061         * suffix specified to the constructor, then load that class, locate 
062         * the appropriate rules-adding method on that class, and return an 
063         * object encapsulating that info.
064         * <p>
065         * If there is no such class, then just return null.
066         * <p>
067         * The returned object (when non-null) will invoke the target method
068         * on the selected class whenever its addRules method is invoked. The
069         * target method is expected to have the following prototype:
070         * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
071         */
072        public RuleLoader findLoader(Digester digester, Class<?> pluginClass, Properties p)
073                                throws PluginException {
074    
075            String rulesClassName = pluginClass.getName() + rulesClassSuffix;
076    
077            Class<?> rulesClass = null;
078            try {
079                rulesClass = digester.getClassLoader().loadClass(rulesClassName);
080            } catch(ClassNotFoundException cnfe) {
081                // ok, ignore
082            }
083    
084            if (rulesClass == null) {
085                // nope, no rule-info class in the classpath
086                return null;
087            }
088            
089            if (methodName == null) {
090                methodName = DFLT_METHOD_NAME;
091            }
092            
093            return new LoaderFromClass(rulesClass, methodName);
094        }
095    }
096