001/* $Id: FinderFromDfltClass.java 471661 2006-11-06 08:09:25Z skitching $
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 
019package org.apache.commons.digester.plugins.strategies;
020
021import java.util.Properties;
022import org.apache.commons.digester.Digester;
023import org.apache.commons.digester.plugins.RuleFinder;
024import org.apache.commons.digester.plugins.RuleLoader;
025import 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
034public 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