001/* $Id: FinderFromDfltMethod.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 java.lang.reflect.Method;
023
024import org.apache.commons.digester.Digester;
025import org.apache.commons.digester.plugins.RuleFinder;
026import org.apache.commons.digester.plugins.RuleLoader;
027import org.apache.commons.digester.plugins.PluginException;
028
029/**
030 * A rule-finding algorithm which looks for a method with a specific name
031 * on the plugin class.
032 *
033 * @since 1.6
034 */
035
036public class FinderFromDfltMethod extends RuleFinder {
037    public static String DFLT_METHOD_NAME = "addRules";
038
039    private String methodName;
040    
041    /** See {@link #findLoader}. */
042    public FinderFromDfltMethod() { 
043        this(DFLT_METHOD_NAME);
044    }
045
046    /**
047     * Create a rule-finder which invokes a specific method on the plugin
048     * class whenever dynamic rules for a plugin need to be loaded. See the 
049     * findRules method for more info.
050     *
051     * @param methodName must be non-null.
052     */
053    public FinderFromDfltMethod(String methodName) { 
054        this.methodName = methodName;
055    }
056    
057    /**
058     * If there exists on the plugin class a method with name matching the 
059     * constructor's methodName value then locate the appropriate Method on 
060     * the plugin class and return an object encapsulating that info.
061     * <p>
062     * If there is no matching method then just return null.
063     * <p>
064     * The returned object (when non-null) will invoke the target method
065     * on the plugin class whenever its addRules method is invoked. The
066     * target method is expected to have the following prototype:
067     * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
068     */
069    public RuleLoader findLoader(Digester d, Class pluginClass, Properties p)
070                        throws PluginException {
071
072        Method rulesMethod = LoaderFromClass.locateMethod(pluginClass, methodName);
073        if (rulesMethod == null) {
074            return null;
075        }
076        
077        return new LoaderFromClass(pluginClass, rulesMethod);
078    }
079}
080