001 /* $Id: FinderFromResource.java 729125 2008-12-23 21:21:07Z rahul $
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
019 package org.apache.commons.digester.plugins.strategies;
020
021 import java.util.Properties;
022 import java.io.InputStream;
023
024 import org.apache.commons.digester.Digester;
025 import org.apache.commons.digester.plugins.RuleFinder;
026 import org.apache.commons.digester.plugins.RuleLoader;
027 import 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
037 public 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