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