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
024 import org.apache.commons.digester3.Digester;
025 import org.apache.commons.digester3.plugins.PluginException;
026 import org.apache.commons.digester3.plugins.RuleFinder;
027 import 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 */
035 public 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 }