ClassFileTransformer (Java 2 Platform SE 5.0) (original) (raw)

java.lang.instrument

Interface ClassFileTransformer

public interface ClassFileTransformer

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.

Note the term class file is used as defined in the chapterThe class File Format of The Java Virtual Machine Specification, to mean a sequence of bytes in class file format, whether or not they reside in a file.

Since:

JDK1.5

Method Summary
byte[]	[transform](../../../java/lang/instrument/ClassFileTransformer.html#transform%28java.lang.ClassLoader, java.lang.String, java.lang.Class, java.security.ProtectionDomain, byte[]%29)(ClassLoader loader,String className,Class<?> classBeingRedefined,ProtectionDomain protectionDomain, byte[] classfileBuffer) The implementation of this method may transform the supplied class file and return a new replacement class file.

Method Summary

byte[]

[transform](../../../java/lang/instrument/ClassFileTransformer.html#transform%28java.lang.ClassLoader, java.lang.String, java.lang.Class, java.security.ProtectionDomain, byte[]%29)(ClassLoader loader,String className,Class<?> classBeingRedefined,ProtectionDomain protectionDomain, byte[] classfileBuffer) The implementation of this method may transform the supplied class file and return a new replacement class file.

Method Detail

transform

byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException

The implementation of this method may transform the supplied class file and return a new replacement class file.

Once a transformer has been registered withInstrumentation.addTransformer, the transformer will be called for every new class definition and every class redefinition. The request for a new class definition is made with[ClassLoader.defineClass](../../../java/lang/ClassLoader.html#defineClass%28byte[], int, int%29). The request for a class redefinition is made withInstrumentation.redefineClasses or its native equivalents. The transformer is called during the processing of the request, before the class file bytes have been verified or applied.

If the implementing method determines that no transformations are needed, it should return null. Otherwise, it should create a new byte[] array, copy the input classfileBuffer into it, along with all desired transformations, and return the new array. The input classfileBuffer must not be modified.

In the redefine case, the transformer must support the redefinition semantics. If a class that the transformer changed during initial definition is later redefined, the transformer must insure that the second class output class file is a legal redefinition of the first output class file.

If the transformer believes the classFileBuffer does not represent a validly formatted class file, it should throw an IllegalClassFormatException. Subsequent transformers will still be called and the load or redefine will still be attempted. Throwing an IllegalClassFormatException thus has the same effect as returning null but facilitates the logging or debugging of format corruptions.

Parameters:

loader - the defining loader of the class to be transformed, may be null if the bootstrap loader

className - the name of the class in the internal form of fully qualified class and interface names as defined in_The Java Virtual Machine Specification_. For example, "java/util/List".

classBeingRedefined - if this is a redefine, the class being redefined, otherwise null

protectionDomain - the protection domain of the class being defined or redefined

classfileBuffer - the input byte buffer in class file format - must not be modified

Returns:

a well-formed class file buffer (the result of the transform), or null if no transform is performed.

Throws:

[IllegalClassFormatException](../../../java/lang/instrument/IllegalClassFormatException.html "class in java.lang.instrument") - if the input does not represent a well-formed class file

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.