ClassResolver


1   // Copyright 2004, 2005 The Apache Software Foundation
2   //
3   // Licensed under the Apache License, Version 2.0 (the "License");
4   // you may not use this file except in compliance with the License.
5   // You may obtain a copy of the License at
6   //
7   //     http://www.apache.org/licenses/LICENSE-2.0
8   //
9   // Unless required by applicable law or agreed to in writing, software
10  // distributed under the License is distributed on an "AS IS" BASIS,
11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12  // See the License for the specific language governing permissions and
13  // limitations under the License.
14  
15  package org.apache.hivemind;
16  
17  import java.net.URL  ;
18  
19  /**
20   * An object which is used to resolve classes and class-path resources. This is needed because, in
21   * an application server, different class loaders may be involved in loading different HiveMind
22   * modules. For example, the HiveMind library may be on the system claasspath, and modules may
23   * include EJBs and WARs, each loaded by a different classloader.
24   * <p>
25   * The class loader for the framework needs to be able to see resources in the application, but the
26   * application's class loader is a descendent of the framework's class loader. To resolve this, we
27   * need a 'hook', an instance that provides access to the application's class loader.
28   * 
29   * @author Howard Lewis Ship
30   */
31  
32  public interface ClassResolver
33  {
34      /**
35       * Forwarded, unchanged, to the class loader. Returns null if the resource is not found.
36       */
37  
38      public URL   getResource(String   name);
39  
40      /**
41       * Forwarded, to the the method <code>Class.forName(String, boolean, ClassLoader)</code>,
42       * using the resolver's class loader.
43       * <p>
44       * Since 1.1, the type may include primitive types and arrays (of primitives or of objects).
45       * 
46       * @throws ApplicationRuntimeException
47       *             on any error.
48       */
49  
50      public Class   findClass(String   type);
51  
52      /**
53       * Like {@link #findClass(String)}, but simply returns null if the class does not exist (i.e.,
54       * if {@link ClassNotFoundException} is thrown). This is used in certain spots when (typically)
55       * the exact package for a class is not known.
56       */
57  
58      public Class   checkForClass(String   type);
59  
60      /**
61       * Returns a {@link java.lang.ClassLoader} that can see all the classes the resolver can access.
62       */
63  
64      public ClassLoader   getClassLoader();
65  }
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