001/* $Id: FinderFromMethod.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 expects the caller to specify a methodname
029 * as a plugin property, where the method exists on the plugin class.
030 *
031 * @since 1.6
032 */
033
034public class FinderFromMethod extends RuleFinder {
035    /**
036     * Xml attribute that needs to be present on a plugin declaration
037     * in order to specify the method to load rules from.
038     */
039    public static String DFLT_METHOD_ATTR = "method";
040    
041    /** See {@link #findLoader}. */
042    private String methodAttr;
043    
044    /** Constructor. */
045    public FinderFromMethod() {
046        this(DFLT_METHOD_ATTR);
047    }
048
049    /** See {@link #findLoader}. */
050    public FinderFromMethod(String methodAttr) { 
051        this.methodAttr = methodAttr;
052    }
053    
054    /**
055     * If there exists a property with the name matching constructor param
056     * methodAttr, then locate the appropriate Method on the plugin class 
057     * and return an object encapsulating that info.
058     * <p>
059     * If there is no matching property provided, then just return null.
060     * <p>
061     * The returned object (when non-null) will invoke the target method
062     * on the plugin class whenever its addRules method is invoked. The
063     * target method is expected to have the following prototype:
064     * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
065     */
066    public RuleLoader findLoader(Digester d, Class pluginClass, Properties p)
067                        throws PluginException {
068
069        String methodName = p.getProperty(methodAttr);
070        if (methodName == null) {
071            // nope, user hasn't requested dynamic rules to be loaded
072            // from a specific class.
073            return null;
074        }
075        
076        return new LoaderFromClass(pluginClass, methodName);
077    }
078}
079