/*
* @(#)ClassFileTransformer.java 1.9 06/05/08
*
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang.instrument;
import java.security.ProtectionDomain;
/*
* Copyright 2003 Wily Technology, Inc.
*/
/**
* An agent provides an implementation of this interface in order
* to transform class files.
* The transformation occurs before the class is defined by the JVM.
* <P>
* Note the term <i>class file</i> is used as defined in the chapter
* <a href="http://java.sun.com/docs/books/vmspec/2nd-edition/html/ClassFile.doc.html#80959">The class File Format</a>
* of <i>The Java Virtual Machine Specification</i>, to mean a sequence
* of bytes in class file format, whether or not they reside in a file.
*
* @see java.lang.instrument.Instrumentation
* @see java.lang.instrument.Instrumentation#addTransformer
* @see java.lang.instrument.Instrumentation#removeTransformer
* @since 1.5
*/
public interface ClassFileTransformer {
/**
* The implementation of this method may transform the supplied class file and
* return a new replacement class file.
*
* <P>
* There are two kinds of transformers, determined by the <code>canRetransform</code>
* parameter of
* {@link java.lang.instrument.Instrumentation#addTransformer(ClassFileTransformer,boolean)}:
* <ul>
* <li><i>retransformation capable</i> transformers that were added with
* <code>canRetransform</code> as true
* </li>
* <li><i>retransformation incapable</i> transformers that were added with
* <code>canRetransform</code> as false or where added with
* {@link java.lang.instrument.Instrumentation#addTransformer(ClassFileTransformer)}
* </li>
* </ul>
*
* <P>
* Once a transformer has been registered with
* {@link java.lang.instrument.Instrumentation#addTransformer(ClassFileTransformer,boolean)
* addTransformer},
* the transformer will be called for every new class definition and every class redefinition.
* Retransformation capable transformers will also be called on every class retransformation.
* The request for a new class definition is made with
* {@link java.lang.ClassLoader#defineClass ClassLoader.defineClass}
* or its native equivalents.
* The request for a class redefinition is made with
* {@link java.lang.instrument.Instrumentation#redefineClasses Instrumentation.redefineClasses}
* or its native equivalents.
* The request for a class retransformation is made with
* {@link java.lang.instrument.Instrumentation#retransformClasses Instrumentation.retransformClasses}
* or its native equivalents.
* The transformer is called during the processing of the request, before the class file bytes
* have been verified or applied.
* When there are multiple transformers, transformations are composed by chaining the
* <code>transform</code> calls.
* That is, the byte array returned by one call to <code>transform</code> becomes the input
* (via the <code>classfileBuffer</code> parameter) to the next call.
*
* <P>
* Transformations are applied in the following order:
* <ul>
* <li>Retransformation incapable transformers
* </li>
* <li>Retransformation incapable native transformers
* </li>
* <li>Retransformation capable transformers
* </li>
* <li>Retransformation capable native transformers
* </li>
* </ul>
*
* <P>
* For retransformations, the retransformation incapable transformers are not
* called, instead the result of the previous transformation is reused.
* In all other cases, this method is called.
* Within each of these groupings, transformers are called in the order registered.
* Native transformers are provided by the <code>ClassFileLoadHook</code> event
* in the Java Virtual Machine Tool Interface).
*
* <P>
* The input (via the <code>classfileBuffer</code> parameter) to the first
* transformer is:
* <ul>
* <li>for new class definition,
* the bytes passed to <code>ClassLoader.defineClass</code>
* </li>
* <li>for class redefinition,
* <code>definitions.getDefinitionClassFile()</code> where
* <code>definitions</code> is the parameter to
* {@link java.lang.instrument.Instrumentation#redefineClasses
* Instrumentation.redefineClasses}
* </li>
* <li>for class retransformation,
* the bytes passed to the new class definition or, if redefined,
* the last redefinition, with all transformations made by retransformation
* incapable transformers reapplied automatically and unaltered;
* for details see
* {@link java.lang.instrument.Instrumentation#retransformClasses
* Instrumentation.retransformClasses}
* </li>
* </ul>
*
* <P>
* If the implementing method determines that no transformations are needed,
* it should return <code>null</code>.
* Otherwise, it should create a new <code>byte[]</code> array,
* copy the input <code>classfileBuffer</code> into it,
* along with all desired transformations, and return the new array.
* The input <code>classfileBuffer</code> must not be modified.
*
* <P>
* In the retransform and redefine cases,
* the transformer must support the redefinition semantics:
* if a class that the transformer changed during initial definition is later
* retransformed or redefined, the
* transformer must insure that the second class output class file is a legal
* redefinition of the first output class file.
*
* <P>
* If the transformer throws an exception (which it doesn't catch),
* subsequent transformers will still be called and the load, redefine
* or retransform will still be attempted.
* Thus, throwing an exception has the same effect as returning <code>null</code>.
* To prevent unexpected behavior when unchecked exceptions are generated
* in transformer code, a transformer can catch <code>Throwable</code>.
* If the transformer believes the <code>classFileBuffer</code> does not
* represent a validly formatted class file, it should throw
* an <code>IllegalClassFormatException</code>;
* while this has the same effect as returning null. it facilitates the
* logging or debugging of format corruptions.
*
* @param loader the defining loader of the class to be transformed,
* may be <code>null</code> if the bootstrap loader
* @param className the name of the class in the internal form of fully
* qualified class and interface names as defined in
* <i>The Java Virtual Machine Specification</i>.
* For example, <code>"java/util/List"</code>.
* @param classBeingRedefined if this is triggered by a redefine or retransform,
* the class being redefined or retransformed;
* if this is a class load, <code>null</code>
* @param protectionDomain the protection domain of the class being defined or redefined
* @param classfileBuffer the input byte buffer in class file format - must not be modified
*
* @throws IllegalClassFormatException if the input does not represent a well-formed class file
* @return a well-formed class file buffer (the result of the transform),
or <code>null</code> if no transform is performed.
* @see Instrumentation#redefineClasses
*/
byte[]
transform( ClassLoader loader,
String className,
Class<?> classBeingRedefined,
ProtectionDomain protectionDomain,
byte[] classfileBuffer)
throws IllegalClassFormatException;
}
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