001 /* $Id: RuleFinder.java 992060 2010-09-02 19:09:47Z simonetripodi $
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 package org.apache.commons.digester.plugins;
019
020 import java.util.Properties;
021 import org.apache.commons.digester.Digester;
022
023 /**
024 * Each concrete implementation of RuleFinder is an algorithm for
025 * locating a source of digester rules for a plugin. The algorithm may
026 * use info explicitly provided by the user as part of the plugin
027 * declaration, or not (in which case the concrete RuleFinder subclass
028 * typically has Dflt as part of its name).
029 * <p>
030 * Instances of this class can also be regarded as a Factory for RuleLoaders,
031 * except that an instance of a RuleLoader is only created if the particular
032 * finder algorithm can locate a suitable source of rules given the plugin
033 * class and associated properties.
034 * <p>
035 * This is an abstract class rather than an interface in order to make
036 * it possible to enhance this class in future without breaking binary
037 * compatibility; it is possible to add methods to an abstract class, but
038 * not to an interface.
039 *
040 * @since 1.6
041 */
042
043 public abstract class RuleFinder {
044
045 /**
046 * Apply the finder algorithm to attempt to locate a source of
047 * digester rules for the specified plugin class.
048 * <p>
049 * This method is invoked when a plugin is declared by the user, either
050 * via an explicit use of PluginDeclarationRule, or implicitly via an
051 * "inline declaration" where the declaration and use are simultaneous.
052 * <p>
053 * If dynamic rules for the specified plugin class are located, then
054 * the RuleFinder will return a RuleLoader object encapsulating those
055 * rules, and this object will be invoked each time the user actually
056 * requests an instance of the declared plugin class, to load the
057 * custom rules associated with that plugin instance.
058 * <p>
059 * If no dynamic rules can be found, null is returned. This is not an
060 * error; merely an indication that this particular algorithm found
061 * no matches.
062 * <p>
063 * The properties object holds any xml attributes the user may have
064 * specified on the plugin declaration in order to indicate how to locate
065 * the plugin rules.
066 * <p>
067 * @throws PluginConfigurationException if the algorithm finds a source
068 * of rules, but there is something invalid about that source.
069 */
070
071 public abstract RuleLoader findLoader(
072 Digester d, Class<?> pluginClass,
073 Properties p) throws PluginException;
074 }
075