001 /* $Id: LoaderFromClass.java 472842 2006-11-09 10:19:56Z 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
019 package org.apache.commons.digester.plugins.strategies;
020
021 import java.lang.reflect.Method;
022
023 import org.apache.commons.digester.Digester;
024 import org.apache.commons.beanutils.MethodUtils;
025 import org.apache.commons.logging.Log;
026 import org.apache.commons.digester.plugins.RuleLoader;
027 import org.apache.commons.digester.plugins.PluginException;
028
029 /**
030 * A RuleLoader which invokes a static method on a target class, leaving that
031 * method to actually instantiate and add new rules to a Digester instance.
032 *
033 * @since 1.6
034 */
035
036 public class LoaderFromClass extends RuleLoader {
037
038 private Class rulesClass;
039 private Method rulesMethod;
040
041 /** Constructor. */
042 public LoaderFromClass(Class rulesClass, Method rulesMethod) {
043 this.rulesClass = rulesClass;
044 this.rulesMethod = rulesMethod;
045 }
046
047 /** Constructor. */
048 public LoaderFromClass(Class rulesClass, String methodName)
049 throws PluginException {
050
051 Method method = locateMethod(rulesClass, methodName);
052
053 if (method == null) {
054 throw new PluginException(
055 "rule class " + rulesClass.getName()
056 + " does not have method " + methodName
057 + " or that method has an invalid signature.");
058 }
059
060 this.rulesClass = rulesClass;
061 this.rulesMethod = method;
062 }
063
064 /**
065 * Just invoke the target method.
066 */
067 public void addRules(Digester d, String path) throws PluginException {
068 Log log = d.getLogger();
069 boolean debug = log.isDebugEnabled();
070 if (debug) {
071 log.debug(
072 "LoaderFromClass loading rules for plugin at path ["
073 + path + "]");
074 }
075
076 try {
077 Object[] params = {d, path};
078 rulesMethod.invoke(null, params);
079 } catch (Exception e) {
080 throw new PluginException(
081 "Unable to invoke rules method " + rulesMethod
082 + " on rules class " + rulesClass, e);
083 }
084 }
085
086 /**
087 * Find a method on the specified class whose name matches methodName,
088 * and whose signature is:
089 * <code> public static void foo(Digester d, String patternPrefix);</code>.
090 *
091 * @return null if no such method exists.
092 */
093 public static Method locateMethod(Class rulesClass, String methodName)
094 throws PluginException {
095
096 Class[] paramSpec = { Digester.class, String.class };
097 Method rulesMethod = MethodUtils.getAccessibleMethod(
098 rulesClass, methodName, paramSpec);
099
100 return rulesMethod;
101 }
102 }
103