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The Apache Commons Digester package lets you configure an XML to Java object mapping module which triggers certain actions called rules whenever a particular pattern of nested XML elements is recognized.

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package org.apache.commons.digester3.plugins.strategies;

/*
 * 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.
 */

import java.util.Properties;
import java.lang.reflect.Method;

import org.apache.commons.digester3.Digester;
import org.apache.commons.digester3.plugins.PluginException;
import org.apache.commons.digester3.plugins.RuleFinder;
import org.apache.commons.digester3.plugins.RuleLoader;

/**
 * A rule-finding algorithm which looks for a method with a specific name on the plugin class.
 * 
 * @since 1.6
 */
public class FinderFromDfltMethod
    extends RuleFinder
{
    private static final String DFLT_METHOD_NAME = "addRules";

    private final String methodName;

    /** See {@link #findLoader}. */
    public FinderFromDfltMethod()
    {
        this( DFLT_METHOD_NAME );
    }

    /**
     * Create a rule-finder which invokes a specific method on the plugin class whenever dynamic rules for a plugin need
     * to be loaded. See the findRules method for more info.
     * 
     * @param methodName must be non-null.
     */
    public FinderFromDfltMethod( String methodName )
    {
        this.methodName = methodName;
    }

    /**
     * If there exists on the plugin class a method with name matching the constructor's methodName value then locate
     * the appropriate Method on the plugin class and return an object encapsulating that info.
     * 
     * If there is no matching method then just return null.
     * 
     * The returned object (when non-null) will invoke the target method on the plugin class whenever its addRules
     * method is invoked. The target method is expected to have the following prototype:
     *  public static void xxxxx(Digester d, String patternPrefix); 
     *
     * @param d The digester instance where locating plugin classes
     * @param pluginClass The plugin Java class
     * @param p The properties object that holds any xml attributes the user may have specified on the plugin
     *          declaration in order to indicate how to locate the plugin rules.
     * @return a source of digester rules for the specified plugin class.
     * @throws PluginException if the algorithm finds a source of rules, but there is something invalid
     *         about that source.
     */
    @Override
    public RuleLoader findLoader( Digester d, Class pluginClass, Properties p )
        throws PluginException
    {

        Method rulesMethod = LoaderFromClass.locateMethod( pluginClass, methodName );
        if ( rulesMethod == null )
        {
            return null;
        }

        return new LoaderFromClass( pluginClass, rulesMethod );
    }

}