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     
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 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    
034    public 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