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1   /*
2    * Copyright (c) 2009 QOS.ch All rights reserved.
3    * 
4    * Permission is hereby granted, free of charge, to any person obtaining a copy
5    * of this software and associated documentation files (the "Software"), to deal
6    * in the Software without restriction, including without limitation the rights
7    * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
8    * copies of the Software, and to permit persons to whom the Software is
9    * furnished to do so, subject to the following conditions:
10   * 
11   * The above copyright notice and this permission notice shall be included in
12   * all copies or substantial portions of the Software.
13   * 
14   * THE SOFTWARE IS PROVIDED "AS  IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
17   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
18   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
19   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
20   * SOFTWARE.
21   */
22  package ch.qos.cal10n.plugins;
23  
24  import java.net.URL;
25  import java.net.URLClassLoader;
26  
27  /**
28   * An almost trivial no fuss implementation of a class loader following the
29   * child-first delegation model.
30   * 
31   * @author Ceki Gülcü
32   */
33  public class ThisFirstClassLoader extends URLClassLoader {
34  
35    public ThisFirstClassLoader(URL[] urls) {
36      super(urls);
37    }
38  
39    public ThisFirstClassLoader(URL[] urls, ClassLoader parent) {
40      super(urls, parent);
41    }
42  
43    public void addURL(URL url) {
44      super.addURL(url);
45    }
46  
47    @Override
48    public Class<?> loadClass(String name) throws ClassNotFoundException {
49      return loadClass(name, false);
50    }
51  
52    /**
53     * We override the parent-first behavior established by java.lang.Classloader.
54     * 
55     * The implementation is surprisingly straightforward.
56     */
57    protected Class<?> loadClass(String name, boolean resolve)
58        throws ClassNotFoundException {
59  
60      // Treating IMessageKeyVerifier as a special case is the whole point of the
61      // exercise.
62      if (name.equals("ch.qos.cal10n.verifier.IMessageKeyVerifier")) {
63        return super.loadClass(name, resolve);
64      }
65  
66      // First, check if the class has already been loaded
67      Class<?> c = findLoadedClass(name);
68  
69      // if not loaded, search the local (child) resources
70      if (c == null) {
71        try {
72          c = findClass(name);
73        } catch (ClassNotFoundException cnfe) {
74          // ignore
75        }
76      }
77  
78      // if we could not find it, delegate to parent
79      // Note that we don't attempt to catch any ClassNotFoundException
80      if (c == null) {
81        if (getParent() != null) {
82          c = getParent().loadClass(name);
83        } else {
84          c = getSystemClassLoader().loadClass(name);
85        }
86      }
87  
88      if (resolve) {
89        resolveClass(c);
90      }
91  
92      return c;
93    }
94  }