001 /* $Id: FinderFromFile.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 import java.io.FileInputStream;
024 import java.io.IOException;
025
026 import org.apache.commons.digester.Digester;
027 import org.apache.commons.digester.plugins.RuleFinder;
028 import org.apache.commons.digester.plugins.RuleLoader;
029 import org.apache.commons.digester.plugins.PluginException;
030
031 /**
032 * A rule-finding algorithm which expects the user to specify an absolute
033 * or relative path in the plugin declaration.
034 * <p>
035 * The file is expected to contain Digester rules in xmlrules format.
036 *
037 * @since 1.6
038 */
039
040 public class FinderFromFile extends RuleFinder {
041 /**
042 * Xml attribute that needs to be present on a plugin declaration
043 * in order to specify the file to load rules from.
044 */
045 public static String DFLT_FILENAME_ATTR = "file";
046
047 /** See {@link #findLoader}. */
048 private String filenameAttr;
049
050 /** See {@link #findLoader}. */
051 public FinderFromFile() {
052 this(DFLT_FILENAME_ATTR);
053 }
054
055 /** See {@link #findLoader}. */
056 public FinderFromFile(String filenameAttr) {
057 this.filenameAttr = filenameAttr;
058 }
059
060 /**
061 * If there exists a property with the name specified in the constructor,
062 * then load that file, run it through the xmlrules module and return an
063 * object encapsulating those rules.
064 * <p>
065 * If there is no matching property provided, then just return null.
066 * <p>
067 * The returned object (when non-null) will add the selected rules to
068 * the digester whenever its addRules method is invoked.
069 */
070 public RuleLoader findLoader(Digester d, Class<?> pluginClass, Properties p)
071 throws PluginException {
072
073 String rulesFileName = p.getProperty(filenameAttr);
074 if (rulesFileName == null) {
075 // nope, user hasn't requested dynamic rules to be loaded
076 // from a specific file.
077 return null;
078 }
079
080 InputStream is = null;
081 try {
082 is = new FileInputStream(rulesFileName);
083 } catch(IOException ioe) {
084 throw new PluginException(
085 "Unable to process file [" + rulesFileName + "]", ioe);
086 }
087
088 try {
089 RuleLoader loader = new LoaderFromStream(is);
090 return loader;
091 } catch(Exception e) {
092 throw new PluginException(
093 "Unable to load xmlrules from file [" +
094 rulesFileName + "]", e);
095 } finally {
096 try {
097 is.close();
098 } catch(java.io.IOException ioe) {
099 throw new PluginException(
100 "Unable to close stream for file [" +
101 rulesFileName + "]", ioe);
102 }
103 }
104 }
105 }
106