001/* ClassFileTransformer.java -- Implementation of this interface is used by an agent to
002   transform class files.
003   Copyright (C) 2005  Free Software Foundation, Inc.
004
005This file is part of GNU Classpath.
006
007GNU Classpath is free software; you can redistribute it and/or modify
008it under the terms of the GNU General Public License as published by
009the Free Software Foundation; either version 2, or (at your option)
010any later version.
011
012GNU Classpath is distributed in the hope that it will be useful, but
013WITHOUT ANY WARRANTY; without even the implied warranty of
014MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015General Public License for more details.
016
017You should have received a copy of the GNU General Public License
018along with GNU Classpath; see the file COPYING.  If not, write to the
019Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02002110-1301 USA.
021
022Linking this library statically or dynamically with other modules is
023making a combined work based on this library.  Thus, the terms and
024conditions of the GNU General Public License cover the whole
025combination.
026
027As a special exception, the copyright holders of this library give you
028permission to link this library with independent modules to produce an
029executable, regardless of the license terms of these independent
030modules, and to copy and distribute the resulting executable under
031terms of your choice, provided that you also meet, for each linked
032independent module, the terms and conditions of the license of that
033module.  An independent module is a module which is not derived from
034or based on this library.  If you modify this library, you may extend
035this exception to your version of the library, but you are not
036obligated to do so.  If you do not wish to do so, delete this
037exception statement from your version. */
038
039
040package java.lang.instrument;
041
042import java.security.ProtectionDomain;
043
044/**
045 * This interface should be implemented by classes wishing to transform
046 * classes bytecode when defining or redefining classes.
047 *
048 * @author Nicolas Geoffray (nicolas.geoffray@menlina.com)
049 * @see Instrumentation
050 * @see Instrumentation#addTransformer(java.lang.instrument.ClassFileTransformer)
051 * @see Instrumentation#removeTransformer(java.lang.instrument.ClassFileTransformer)
052 * @since 1.5
053 */
054public interface ClassFileTransformer
055{
056
057  /**
058   * Implementation of this method transforms a class by redefining its
059   * bytecodes. Once a ClassFileTransformer object registers itself to the
060   * Instrumentation object, this method will be called each time a class is
061   * defined (<code>ClassLoader.defineClass</code>) or redefined
062   * (<code>Instrumentation.redefineClasses</code>)
063   * @param loader the loader of the class
064   * @param className the name of the class with packages separated with "/"
065   * @param classBeingRedefined the class being redefined if it's the case,
066   * null otherwise
067   * @param protectionDomain the protection domain of the class being defined or
068   * redefined
069   * @param classfileBuffer the input byte buffer in class file format
070   * 
071   * @return a class file buffer or null when no transformation has been performed
072   * 
073   * @throws IllegalClassFormatException if the byte buffer does not represent
074   * a well-formed class file
075   * @see Instrumentation#redefineClasses(java.lang.instrument.ClassDefinition[])
076   *
077   */
078  byte[] transform(ClassLoader loader,
079                 String className,
080                 Class<?> classBeingRedefined,
081                 ProtectionDomain protectionDomain,
082                 byte[] classfileBuffer)
083                 throws IllegalClassFormatException;
084}
085