1 /*
2 * Copyright 2002-2004 The Apache Software Foundation
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16 package org.apache.commons.clazz.common;
17
18 import java.util.ArrayList;
19 import java.util.Collections;
20 import java.util.List;
21
22 import org.apache.commons.clazz.Clazz;
23 import org.apache.commons.clazz.ClazzLoader;
24 import org.apache.commons.clazz.ModelClazzLoader;
25
26 /**
27 * Aggregates multiple ClazzLoaders, which are invoked one after another
28 * according to the ChainOfResponsibility pattern. Note that member clazz
29 * loaders are invoked in the order reverse to the order they were added.
30 *
31 * @author <a href="mailto:dmitri@apache.org">Dmitri Plotnikov</a>
32 * @version $Id: GroupClazzLoader.java 155436 2005-02-26 13:17:48Z dirkv $
33 */
34 public class GroupClazzLoader extends ClazzLoader {
35 /**
36 * List of member loaders. Note that the list is always iterated in the
37 * reverse direction, so the loaded add last is the one invoked first.
38 */
39 protected ArrayList loaders = new ArrayList();
40
41 public GroupClazzLoader(ModelClazzLoader modelClazzLoader) {
42 super(modelClazzLoader);
43 }
44
45 /**
46 * Returns true if the supplied loader "belongs" in the group and can be
47 * added to it. The default implementation returns true.
48 */
49 public boolean canAddClazzLoader(ClazzLoader loader) {
50 return true;
51 }
52
53 /**
54 * Adds a ClazzLoader to the group. ClazzLoaders added last are invoked
55 * first. Before the group adds the loader to itself, it checks if any
56 * of its members are groups themselves and, if so, tries to add the new
57 * loader to those subgroups.
58 */
59 public void addClazzLoader(ClazzLoader loader) {
60 for (int i = loaders.size(); --i >= 0;) {
61 ClazzLoader member = (ClazzLoader) loaders.get(i);
62 if (member instanceof GroupClazzLoader) {
63 GroupClazzLoader group = (GroupClazzLoader) member;
64 if (group.canAddClazzLoader(loader)) {
65 group.addClazzLoader(loader);
66 return;
67 }
68 }
69 }
70 loaders.add(loader);
71 }
72
73 /**
74 * Returns true iff this group has a member loader that has or can construct
75 * a Clazz for the supplied instance.
76 */
77 public boolean isMember(Object instance) {
78 // Note the reverse order
79 for (int i = loaders.size(); --i >= 0;) {
80 ClazzLoader loader = (ClazzLoader) loaders.get(i);
81 if (loader.isMember(instance)) {
82 return true;
83 }
84 }
85 return false;
86 }
87
88 public String getClazzName(Object instance) {
89 // Note the reverse order
90 for (int i = loaders.size(); --i >= 0;) {
91 ClazzLoader loader = (ClazzLoader) loaders.get(i);
92 String name = loader.getClazzName(instance);
93 if (name != null) {
94 return name;
95 }
96 }
97 return null;
98 }
99
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 }