001    package org.apache.commons.digester3.plugins.strategies;
002    
003    /*
004     * Licensed to the Apache Software Foundation (ASF) under one
005     * or more contributor license agreements.  See the NOTICE file
006     * distributed with this work for additional information
007     * regarding copyright ownership.  The ASF licenses this file
008     * to you under the Apache License, Version 2.0 (the
009     * "License"); you may not use this file except in compliance
010     * with the License.  You may obtain a copy of the License at
011     *
012     *   http://www.apache.org/licenses/LICENSE-2.0
013     *
014     * Unless required by applicable law or agreed to in writing,
015     * software distributed under the License is distributed on an
016     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
017     * KIND, either express or implied.  See the License for the
018     * specific language governing permissions and limitations
019     * under the License.
020     */
021    
022    import java.util.Properties;
023    import java.lang.reflect.Method;
024    
025    import org.apache.commons.digester3.Digester;
026    import org.apache.commons.digester3.plugins.PluginException;
027    import org.apache.commons.digester3.plugins.RuleFinder;
028    import org.apache.commons.digester3.plugins.RuleLoader;
029    
030    /**
031     * A rule-finding algorithm which looks for a method with a specific name on the plugin class.
032     * 
033     * @since 1.6
034     */
035    public class FinderFromDfltMethod
036        extends RuleFinder
037    {
038        private static final String DFLT_METHOD_NAME = "addRules";
039    
040        private final String methodName;
041    
042        /** See {@link #findLoader}. */
043        public FinderFromDfltMethod()
044        {
045            this( DFLT_METHOD_NAME );
046        }
047    
048        /**
049         * Create a rule-finder which invokes a specific method on the plugin class whenever dynamic rules for a plugin need
050         * to be loaded. See the findRules method for more info.
051         * 
052         * @param methodName must be non-null.
053         */
054        public FinderFromDfltMethod( String methodName )
055        {
056            this.methodName = methodName;
057        }
058    
059        /**
060         * If there exists on the plugin class a method with name matching the constructor's methodName value then locate
061         * the appropriate Method on the plugin class and return an object encapsulating that info.
062         * <p>
063         * If there is no matching method then just return null.
064         * <p>
065         * The returned object (when non-null) will invoke the target method on the plugin class whenever its addRules
066         * method is invoked. The target method is expected to have the following prototype:
067         * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
068         *
069         * @param d The digester instance where locating plugin classes
070         * @param pluginClass The plugin Java class
071         * @param p The properties object that holds any xml attributes the user may have specified on the plugin
072         *          declaration in order to indicate how to locate the plugin rules.
073         * @return a source of digester rules for the specified plugin class.
074         * @throws PluginException if the algorithm finds a source of rules, but there is something invalid
075         *         about that source.
076         */
077        @Override
078        public RuleLoader findLoader( Digester d, Class<?> pluginClass, Properties p )
079            throws PluginException
080        {
081    
082            Method rulesMethod = LoaderFromClass.locateMethod( pluginClass, methodName );
083            if ( rulesMethod == null )
084            {
085                return null;
086            }
087    
088            return new LoaderFromClass( pluginClass, rulesMethod );
089        }
090    
091    }