001package 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
022import java.util.Properties;
023import java.lang.reflect.Method;
024
025import org.apache.commons.digester3.Digester;
026import org.apache.commons.digester3.plugins.PluginException;
027import org.apache.commons.digester3.plugins.RuleFinder;
028import 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 */
035public 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}