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;
023
024import org.apache.commons.digester3.Digester;
025import org.apache.commons.digester3.plugins.PluginException;
026import org.apache.commons.digester3.plugins.RuleFinder;
027import org.apache.commons.digester3.plugins.RuleLoader;
028
029/**
030 * A rule-finding algorithm which expects the caller to specify a methodname as a plugin property, where the method
031 * exists on the plugin class.
032 * 
033 * @since 1.6
034 */
035public class FinderFromMethod
036    extends RuleFinder
037{
038
039    /**
040     * Default XML attribute that needs to be present on a plugin declaration in order to specify the method
041     * to load rules from.
042     */
043    private static final String DFLT_METHOD_ATTR = "method";
044
045    /** See {@link #findLoader}. */
046    private final String methodAttr;
047
048    /** Constructor. */
049    public FinderFromMethod()
050    {
051        this( DFLT_METHOD_ATTR );
052    }
053
054    /**
055     * See {@link #findLoader}.
056     *
057     * @param methodAttr The XML attribute that needs to be present on a plugin declaration in order to specify the
058     *        method to load rules from.
059     */
060    public FinderFromMethod( String methodAttr )
061    {
062        this.methodAttr = methodAttr;
063    }
064
065    /**
066     * If there exists a property with the name matching constructor param methodAttr, then locate the appropriate
067     * Method on the plugin class and return an object encapsulating that info.
068     * <p>
069     * If there is no matching property provided, then just return null.
070     * <p>
071     * The returned object (when non-null) will invoke the target method on the plugin class whenever its addRules
072     * method is invoked. The target method is expected to have the following prototype:
073     * <code> public static void xxxxx(Digester d, String patternPrefix); </code>
074     *
075     * @param d The digester instance where locating plugin classes
076     * @param pluginClass The plugin Java class
077     * @param p The properties object that holds any xml attributes the user may have specified on the plugin
078     *          declaration in order to indicate how to locate the plugin rules.
079     * @return a source of digester rules for the specified plugin class.
080     * @throws PluginException if the algorithm finds a source of rules, but there is something invalid
081     *         about that source.
082     */
083    @Override
084    public RuleLoader findLoader( Digester d, Class<?> pluginClass, Properties p )
085        throws PluginException
086    {
087
088        String methodName = p.getProperty( methodAttr );
089        if ( methodName == null )
090        {
091            // nope, user hasn't requested dynamic rules to be loaded
092            // from a specific class.
093            return null;
094        }
095
096        return new LoaderFromClass( pluginClass, methodName );
097    }
098
099}