001/* $Id: FinderFromMethod.java 992060 2010-09-02 19:09:47Z simonetripodi $
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 */
018package org.apache.commons.digester.plugins.strategies;
019
020import java.util.Properties;
021import org.apache.commons.digester.Digester;
022import org.apache.commons.digester.plugins.RuleFinder;
023import org.apache.commons.digester.plugins.RuleLoader;
024import org.apache.commons.digester.plugins.PluginException;
025
026/**
027 * A rule-finding algorithm which expects the caller to specify a methodname
028 * as a plugin property, where the method exists on the plugin class.
029 *
030 * @since 1.6
031 */
032
033public class FinderFromMethod extends RuleFinder {
034    /**
035     * Xml attribute that needs to be present on a plugin declaration
036     * in order to specify the method to load rules from.
037     */
038    public static String DFLT_METHOD_ATTR = "method";
039    
040    /** See {@link #findLoader}. */
041    private String methodAttr;
042    
043    /** Constructor. */
044    public FinderFromMethod() {
045        this(DFLT_METHOD_ATTR);
046    }
047
048    /** See {@link #findLoader}. */
049    public FinderFromMethod(String methodAttr) { 
050        this.methodAttr = methodAttr;
051    }
052    
053    /**
054     * If there exists a property with the name matching constructor param
055     * methodAttr, then locate the appropriate Method on the plugin class 
056     * and return an object encapsulating that info.
057     * <p>
058     * If there is no matching property provided, then just return null.
059     * <p>
060     * The returned object (when non-null) will invoke the target method
061     * on the plugin class whenever its addRules method is invoked. The
062     * target method is expected to have the following prototype:
063     * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
064     */
065    @Override
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