001/* $Id: FinderFromResource.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.util.Properties;
022import java.io.InputStream;
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 expects the user to specify a resource
031 * name (ie a file in the classpath). The file is expected to contain Digester
032 * rules in xmlrules format.
033 *
034 * @since 1.6
035 */
036
037public class FinderFromResource extends RuleFinder {
038    /** 
039     * Name of xml attribute on the plugin declaration which is used
040     * to configure rule-loading for that declaration. 
041     */
042    public static String DFLT_RESOURCE_ATTR = "resource";
043    
044    /** See {@link #findLoader}. */
045    private String resourceAttr;
046    
047    /** Constructor. */
048    public FinderFromResource() {
049        this(DFLT_RESOURCE_ATTR);
050    }
051
052    /** See {@link #findLoader}. */
053    public FinderFromResource(String resourceAttr) { 
054        this.resourceAttr = resourceAttr;
055    }
056    
057    /**
058     * If there exists a property with the name matching constructor param
059     * resourceAttr, then load that file, run it through the xmlrules
060     * module and return an object encapsulating those rules.
061     * <p>
062     * If there is no matching property provided, then just return null.
063     * <p>
064     * The returned object (when non-null) will add the selected rules to
065     * the digester whenever its addRules method is invoked.
066     */
067    public RuleLoader findLoader(Digester d, Class pluginClass, Properties p)
068                        throws PluginException {
069
070        String resourceName = p.getProperty(resourceAttr);
071        if (resourceName == null) {
072            // nope, user hasn't requested dynamic rules to be loaded
073            // from a specific file.
074            return null;
075        }
076        
077        InputStream is = 
078            pluginClass.getClassLoader().getResourceAsStream(
079                resourceName);
080
081        if (is == null) {
082            throw new PluginException(
083                "Resource " + resourceName + " not found.");
084        }
085        
086         return loadRules(d, pluginClass, is, resourceName);
087    }
088    
089    /**
090     * Open the specified resource file (ie a file in the classpath, 
091     * including being within a jar in the classpath), run it through
092     * the xmlrules module and return an object encapsulating those rules.
093     * 
094     * @param d is the digester into which rules will eventually be loaded.
095     * @param pluginClass is the class whose xml params the rules are parsing.
096     * @param is is where the xmlrules will be read from, and must be non-null.
097     * @param resourceName is a string describing the source of the xmlrules,
098     *  for use in generating error messages.
099     */
100    public static RuleLoader loadRules(Digester d, Class pluginClass, 
101                        InputStream is, String resourceName)
102                        throws PluginException {
103
104        try {
105            RuleLoader loader = new LoaderFromStream(is);
106            return loader;
107        } catch(Exception e) {
108            throw new PluginException(
109                "Unable to load xmlrules from resource [" + 
110                resourceName + "]", e);
111        } finally {
112            try {
113                is.close();
114            } catch(java.io.IOException ioe) {
115                throw new PluginException(
116                    "Unable to close stream for resource [" + 
117                    resourceName + "]", ioe);
118            }
119        }
120    }
121}
122