001 /*
002 * Copyright 2002-2004 The Apache Software Foundation
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016 package org.apache.commons.clazz.common;
017
018 import java.util.ArrayList;
019 import java.util.Collections;
020 import java.util.List;
021
022 import org.apache.commons.clazz.Clazz;
023 import org.apache.commons.clazz.ClazzLoader;
024 import org.apache.commons.clazz.ModelClazzLoader;
025
026 /**
027 * Aggregates multiple ClazzLoaders, which are invoked one after another
028 * according to the ChainOfResponsibility pattern. Note that member clazz
029 * loaders are invoked in the order reverse to the order they were added.
030 *
031 * @author <a href="mailto:dmitri@apache.org">Dmitri Plotnikov</a>
032 * @version $Id: GroupClazzLoader.java 155436 2005-02-26 13:17:48Z dirkv $
033 */
034 public class GroupClazzLoader extends ClazzLoader {
035 /**
036 * List of member loaders. Note that the list is always iterated in the
037 * reverse direction, so the loaded add last is the one invoked first.
038 */
039 protected ArrayList loaders = new ArrayList();
040
041 public GroupClazzLoader(ModelClazzLoader modelClazzLoader) {
042 super(modelClazzLoader);
043 }
044
045 /**
046 * Returns true if the supplied loader "belongs" in the group and can be
047 * added to it. The default implementation returns true.
048 */
049 public boolean canAddClazzLoader(ClazzLoader loader) {
050 return true;
051 }
052
053 /**
054 * Adds a ClazzLoader to the group. ClazzLoaders added last are invoked
055 * first. Before the group adds the loader to itself, it checks if any
056 * of its members are groups themselves and, if so, tries to add the new
057 * loader to those subgroups.
058 */
059 public void addClazzLoader(ClazzLoader loader) {
060 for (int i = loaders.size(); --i >= 0;) {
061 ClazzLoader member = (ClazzLoader) loaders.get(i);
062 if (member instanceof GroupClazzLoader) {
063 GroupClazzLoader group = (GroupClazzLoader) member;
064 if (group.canAddClazzLoader(loader)) {
065 group.addClazzLoader(loader);
066 return;
067 }
068 }
069 }
070 loaders.add(loader);
071 }
072
073 /**
074 * Returns true iff this group has a member loader that has or can construct
075 * a Clazz for the supplied instance.
076 */
077 public boolean isMember(Object instance) {
078 // Note the reverse order
079 for (int i = loaders.size(); --i >= 0;) {
080 ClazzLoader loader = (ClazzLoader) loaders.get(i);
081 if (loader.isMember(instance)) {
082 return true;
083 }
084 }
085 return false;
086 }
087
088 public String getClazzName(Object instance) {
089 // Note the reverse order
090 for (int i = loaders.size(); --i >= 0;) {
091 ClazzLoader loader = (ClazzLoader) loaders.get(i);
092 String name = loader.getClazzName(instance);
093 if (name != null) {
094 return name;
095 }
096 }
097 return null;
098 }
099
100 /**
101 * Given a Clazz name, produces the corresponding Clazz by invoking member
102 * loaders one by one until the clazz is found.
103 */
104 public Clazz getClazzForName(String name) {
105 Clazz clazz = null;
106 // Note the reverse order
107 for (int i = loaders.size(); --i >= 0;) {
108 ClazzLoader loader = (ClazzLoader) loaders.get(i);
109 clazz = loader.getClazzForName(name);
110 if (clazz != null) {
111 break;
112 }
113 }
114 return clazz;
115 }
116
117 /**
118 * @see ClazzLoader#defineClazz(String, Class, Class)
119 */
120 public Clazz defineClazz(
121 String name,
122 Class clazzClass,
123 Class instanceClass)
124 {
125 Clazz clazz = null;
126 // Note the reverse order
127 for (int i = loaders.size(); --i >= 0;) {
128 ClazzLoader loader = (ClazzLoader) loaders.get(i);
129 clazz = loader.defineClazz(name, clazzClass, instanceClass);
130 if (clazz != null) {
131 break;
132 }
133 }
134 return clazz;
135 }
136
137 /**
138 * Returns all clazz loaders registered with this group,
139 * in the order of priority
140 */
141 public List getClazzLoaders() {
142 return Collections.unmodifiableList(loaders);
143 }
144
145 /**
146 * Returns clazzloaders matching the supplied Predicate
147 */
148 // public List getClazzLoaders(Predicate predicate) {
149 // }
150 }