1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.discovery;
18
19 import java.net.URL;
20 import java.security.AccessController;
21 import java.security.PrivilegedAction;
22
23 import org.apache.commons.logging.Log;
24 import org.apache.commons.logging.LogFactory;
25
26 /**
27 * 'Resource' located by discovery.
28 * Naming of methods becomes a real pain ('getClass()')
29 * so I've patterned this after ClassLoader...
30 *
31 * I think it works well as it will give users a point-of-reference.
32 *
33 * @param <T> The SPI type
34 */
35 public class ResourceClass<T> extends Resource {
36
37 private static Log log = LogFactory.getLog(ResourceClass.class);
38
39 /**
40 * Sets the {@code Log} for this class.
41 *
42 * @param _log This class {@code Log}
43 * @deprecated This method is not thread-safe
44 */
45 @Deprecated
46 public static void setLog(Log _log) {
47 log = _log;
48 }
49
50 protected Class<? extends T> resourceClass;
51
52 /**
53 * Create a new {@code Resource} class located by discovery.
54 *
55 * @param <S> Any type extends T
56 * @param resourceClass The resource class has to be located
57 * @param resource The resource URL has to be located
58 */
59 public <S extends T> ResourceClass(Class<S> resourceClass, URL resource) {
60 super(resourceClass.getName(), resource, resourceClass.getClassLoader());
61 this.resourceClass = resourceClass;
62 }
63
64 /**
65 * Create a new {@code Resource} class located by discovery.
66 *
67 * @param resourceName The resource class name has to be located
68 * @param resource The resource URL has to be located
69 * @param loader The class loaders holder
70 */
71 public ResourceClass(String resourceName, URL resource, ClassLoader loader) {
72 super(resourceName, resource, loader);
73 }
74
75 /**
76 * Get the value of resourceClass.
77 * Loading the class does NOT guarentee that the class can be
78 * instantiated. Go figure.
79 * The class can be instantiated when the class is linked/resolved,
80 * and all dependencies are resolved.
81 * Various JDKs do this at different times, so beware:
82 * java.lang.NoClassDefFoundError when
83 * calling Class.getDeclaredMethod() (JDK14),
84 * java.lang.reflect.InvocationTargetException
85 * (wrapping java.lang.NoClassDefFoundError) when calling
86 * java.lang.newInstance (JDK13),
87 * and who knows what else..
88 *
89 * @param <S> Any type extends T
90 *
91 * @return value of resourceClass.
92 */
93 public <S extends T> Class<S> loadClass() {
94 if (resourceClass == null && getClassLoader() != null) {
95 if (log.isDebugEnabled()) {
96 log.debug("loadClass: Loading class '" + getName() + "' with " + getClassLoader());
97 }
98
99 resourceClass = AccessController.doPrivileged(
100 new PrivilegedAction<Class<? extends T>>() {
101 public Class<? extends T> run() {
102 try {
103 @SuppressWarnings("unchecked") // this can raise a ClassCastException at runtime
104 Class<S> returned = (Class<S>) getClassLoader().loadClass(getName());
105 return returned;
106 } catch (ClassNotFoundException e) {
107 return null;
108 }
109 }
110 });
111 }
112
113 @SuppressWarnings("unchecked") // this is assumed by default, see the ctor
114 Class<S> returned = (Class<S>) resourceClass;
115 return returned;
116 }
117
118 /**
119 * {@inheritDoc}
120 */
121 @Override
122 public String toString() {
123 return "ResourceClass[" + getName() + ", " + getResource() + ", " + getClassLoader() + "]";
124 }
125
126 }