Commons Digester example source code file (RuleFinder.java)

This example Commons Digester source code file (RuleFinder.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Digester tags/keywords

class, digester, digester, pluginexception, pluginexception, properties, rulefinder, rulefinder, ruleloader, ruleloader, util

The Commons Digester RuleFinder.java source code

/* $Id: RuleFinder.java 992060 2010-09-02 19:09:47Z simonetripodi $
 *
 * 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).
 * <p>
 * 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.
 * <p>
 * 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.
     * <p>
     * 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.
     * <p>
     * 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.
     * <p>
     * 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.
     * <p>
     * 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.
     * <p>
     * @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;
}