org.apache.commons.digester.plugins.RuleFinder Maven / Gradle / Ivy
/* $Id: RuleFinder.java 729120 2008-12-23 21:11:38Z rahul $
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.digester.plugins;
import java.util.Properties;
import org.apache.commons.digester.Digester;
/**
* Each concrete implementation of RuleFinder is an algorithm for
* locating a source of digester rules for a plugin. The algorithm may
* use info explicitly provided by the user as part of the plugin
* declaration, or not (in which case the concrete RuleFinder subclass
* typically has Dflt as part of its name).
*
* Instances of this class can also be regarded as a Factory for RuleLoaders,
* except that an instance of a RuleLoader is only created if the particular
* finder algorithm can locate a suitable source of rules given the plugin
* class and associated properties.
*
* This is an abstract class rather than an interface in order to make
* it possible to enhance this class in future without breaking binary
* compatibility; it is possible to add methods to an abstract class, but
* not to an interface.
*
* @since 1.6
*/
public abstract class RuleFinder {
/**
* Apply the finder algorithm to attempt to locate a source of
* digester rules for the specified plugin class.
*
* This method is invoked when a plugin is declared by the user, either
* via an explicit use of PluginDeclarationRule, or implicitly via an
* "inline declaration" where the declaration and use are simultaneous.
*
* If dynamic rules for the specified plugin class are located, then
* the RuleFinder will return a RuleLoader object encapsulating those
* rules, and this object will be invoked each time the user actually
* requests an instance of the declared plugin class, to load the
* custom rules associated with that plugin instance.
*
* If no dynamic rules can be found, null is returned. This is not an
* error; merely an indication that this particular algorithm found
* no matches.
*
* The properties object holds any xml attributes the user may have
* specified on the plugin declaration in order to indicate how to locate
* the plugin rules.
*
* @throws PluginConfigurationException if the algorithm finds a source
* of rules, but there is something invalid about that source.
*/
public abstract RuleLoader findLoader(
Digester d, Class pluginClass,
Properties p) throws PluginException;
}