001/* $Id: FinderFromDfltResource.java 471661 2006-11-06 08:09:25Z skitching $
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 
019package org.apache.commons.digester.plugins.strategies;
020
021import java.io.InputStream;
022import java.util.Properties;
023
024import org.apache.commons.digester.Digester;
025import org.apache.commons.digester.plugins.RuleFinder;
026import org.apache.commons.digester.plugins.RuleLoader;
027import org.apache.commons.digester.plugins.PluginException;
028
029/**
030 * A rule-finding algorithm which looks for a resource file in the classpath
031 * whose name is derived from the plugin class name plus a specified suffix.
032 * <p>
033 * If the resource-file is found, then it is expected to define a set of
034 * Digester rules in xmlrules format.
035 *
036 * @since 1.6
037 */
038
039public class FinderFromDfltResource extends RuleFinder {
040    public static String DFLT_RESOURCE_SUFFIX = "RuleInfo.xml";
041
042    private String resourceSuffix;
043    
044    /** See {@link #findLoader}. */
045    public FinderFromDfltResource() { 
046        this(DFLT_RESOURCE_SUFFIX);
047    }
048
049    /**
050     * Create a rule-finder which can load an xmlrules file, cache
051     * the rules away, and later add them as a plugin's custom rules
052     * when that plugin is referenced.
053     *
054     * @param resourceSuffix must be non-null.
055     */
056    public FinderFromDfltResource(String resourceSuffix) { 
057        this.resourceSuffix = resourceSuffix;
058    }
059    
060    /**
061     * If there exists a resource file whose name is equal to the plugin
062     * class name + the suffix specified in the constructor, then
063     * load that file, run it through the xmlrules module and return an object 
064     * encapsulating those rules.
065     * <p>
066     * If there is no such resource file, then just return null.
067     * <p>
068     * The returned object (when non-null) will add the selected rules to
069     * the digester whenever its addRules method is invoked.
070     */
071    public RuleLoader findLoader(Digester d, Class pluginClass, Properties p)
072                        throws PluginException {
073
074        String resourceName = 
075            pluginClass.getName().replace('.', '/') 
076                    + resourceSuffix;
077            
078        InputStream is = 
079            pluginClass.getClassLoader().getResourceAsStream(
080                resourceName);
081
082        if (is == null) {
083            // ok, no such resource
084            return null;
085        }
086
087        return FinderFromResource.loadRules(d, pluginClass, is, resourceName);
088    }
089}
090