ClassFileTransformer


1   /*
2    * @(#)ClassFileTransformer.java    1.5 04/05/05
3    *
4    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. 
5    */
6   
7   package java.lang.instrument;
8   
9   
10  import  java.security.ProtectionDomain  ;
11  
12  /*
13   * Copyright 2003 Wily Technology, Inc.
14   */
15  
16  /**
17   * An agent provides an implementation of this interface in order
18   * to transform class files.  
19   * The transformation occurs before the class is defined by the JVM.
20   * <P>
21   * Note the term <i>class file</i> is used as defined in the chapter
22   * <a HREF="http://java.sun.com/docs/books/vmspec/2nd-edition/html/ClassFile.doc.html#80959">The class File Format</a>
23   * of <i>The Java Virtual Machine Specification</i>, to mean a sequence
24   * of bytes in class file format, whether or not they reside in a file.
25   *
26   * @see     java.lang.instrument.Instrumentation
27   * @see     java.lang.instrument.Instrumentation#addTransformer
28   * @see     java.lang.instrument.Instrumentation#removeTransformer
29   * @since   JDK1.5
30   */
31  
32  public interface ClassFileTransformer { 
33      /**
34       * The implementation of this method may transform the supplied class file and 
35       * return a new replacement class file.
36       *
37       * <P>
38       * Once a transformer has been registered with
39       * {@link java.lang.instrument.Instrumentation#addTransformer Instrumentation.addTransformer},
40       * the transformer will be called for every new class definition and every class redefinition.
41       * The request for a new class definition is made with
42       * {@link java.lang.ClassLoader#defineClass ClassLoader.defineClass}.
43       * The request for a class redefinition is made with
44       * {@link java.lang.instrument.Instrumentation#redefineClasses Instrumentation.redefineClasses}
45       * or its native equivalents.
46       * The transformer is called during the processing of the request, before the class file bytes
47       * have been verified or applied.
48       *
49       * <P>
50       * If the implementing method determines that no transformations are needed,
51       * it should return <code>null</code>. 
52       * Otherwise, it should create a new <code>byte[]</code> array,
53       * copy the input <code>classfileBuffer</code> into it,
54       * along with all desired transformations, and return the new array. 
55       * The input <code>classfileBuffer</code> must not be modified.
56       *
57       * <P>
58       * In the redefine case, the transformer must support the redefinition semantics.
59       * If a class that the transformer changed during initial definition is later redefined, the
60       * transformer must insure that the second class output class file is a legal
61       * redefinition of the first output class file.
62       *
63       * <P>
64       * If the transformer believes the <code>classFileBuffer</code> does not
65       * represent a validly formatted class file, it should throw
66       * an <code>IllegalClassFormatException</code>.  Subsequent transformers
67       * will still be called and the load or redefine will still
68       * be attempted.  Throwing an <code>IllegalClassFormatException</code> thus
69       * has the same effect as returning null but facilitates the
70       * logging or debugging of format corruptions.
71       *
72       * @param loader                the defining loader of the class to be transformed,
73       *                              may be <code>null</code> if the bootstrap loader
74       * @param className             the name of the class in the internal form of fully
75       *                              qualified class and interface names as defined in
76       *                              <i>The Java Virtual Machine Specification</i>.  
77       *                              For example, <code>"java/util/List"</code>.
78       * @param classBeingRedefined   if this is a redefine, the class being redefined, 
79       *                              otherwise <code>null</code>
80       * @param protectionDomain      the protection domain of the class being defined or redefined
81       * @param classfileBuffer       the input byte buffer in class file format - must not be modified
82       *
83       * @throws IllegalClassFormatException if the input does not represent a well-formed class file
84       * @return  a well-formed class file buffer (the result of the transform), 
85                  or <code>null</code> if no transform is performed.
86       * @see Instrumentation#redefineClasses
87       */
88      byte[]
89      transform(  ClassLoader           loader,
90                  String                className,
91                  Class  <?>            classBeingRedefined,
92                  ProtectionDomain      protectionDomain,
93                  byte[]              classfileBuffer)
94          throws IllegalClassFormatException  ;
95  } 
96
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