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  
18  package org.apache.commons.beanutils.converters;
19  
20  import java.io.InputStream;
21  import java.io.ByteArrayOutputStream;
22  import java.io.FileNotFoundException;
23  import java.io.IOException;
24  
25  /***
26   * A special classloader useful for testing j2ee-like scenarios.
27   * 
28   * <p>In some tests we want to be able to emulate "container" frameworks,
29   * where code runs in a hierarchy of classloaders, and certain classes may
30   * be loaded by various classloaders in the hierarchy.</p>
31   *
32   * <p>Normally this is done by having certain jars or class-file-directories
33   * in the classpath of some classloaders but not others. This is quite 
34   * difficult difficult to integrate with the build process for the unit
35   * tests though; compiling certain classes and having the output go into
36   * places that is not in the default classpath for the unit tests would be
37   * a major pain.</p>
38   *
39   * <p>So this class takes a sneaky alternative approach: it can grab any class
40   * already loaded by a parent classloader and <i>reload</i> that class via this
41   * classloader. The effect is exactly as if a class (or jar file) had been
42   * present in the classpath for a container's "shared" classloader <i>and</i>
43   * been present in the component-specific classpath too, without any messing
44   * about with the way unit test code is compiled or executed.
45   */
46  
47  public class ClassReloader extends ClassLoader {
48      public ClassReloader(ClassLoader parent) {
49          super(parent);
50      }
51      
52      /***
53       * Given a class already in the classpath of a parent classloader,
54       * reload that class via this classloader.
55       */
56      public Class reload(Class clazz) throws FileNotFoundException, IOException {
57          String className = clazz.getName();
58          String classFile = className.replace('.', '/') + ".class";
59          InputStream classStream = getParent().getResourceAsStream(classFile);
60          
61          if (classStream == null) {
62              throw new FileNotFoundException(classFile);
63          }
64          
65          byte[] buf = new byte[1024];
66          ByteArrayOutputStream baos = new ByteArrayOutputStream();
67          for(;;) {
68              int bytesRead = classStream.read(buf);
69              if (bytesRead == -1)
70                  break;
71              baos.write(buf, 0, bytesRead);
72          }
73          classStream.close();
74          
75          byte[] classData = baos.toByteArray();
76          
77          // now we have the raw class data, let's turn it into a class
78          Class newClass = defineClass(className, classData, 0, classData.length);
79          resolveClass(newClass);
80          return newClass;
81      }
82  }