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    
005    This file is part of GNU Classpath.
006    
007    GNU Classpath is free software; you can redistribute it and/or modify
008    it under the terms of the GNU General Public License as published by
009    the Free Software Foundation; either version 2, or (at your option)
010    any later version.
011    
012    GNU Classpath is distributed in the hope that it will be useful, but
013    WITHOUT ANY WARRANTY; without even the implied warranty of
014    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015    General Public License for more details.
016    
017    You should have received a copy of the GNU General Public License
018    along with GNU Classpath; see the file COPYING.  If not, write to the
019    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
020    02110-1301 USA.
021    
022    Linking this library statically or dynamically with other modules is
023    making a combined work based on this library.  Thus, the terms and
024    conditions of the GNU General Public License cover the whole
025    combination.
026    
027    As a special exception, the copyright holders of this library give you
028    permission to link this library with independent modules to produce an
029    executable, regardless of the license terms of these independent
030    modules, and to copy and distribute the resulting executable under
031    terms of your choice, provided that you also meet, for each linked
032    independent module, the terms and conditions of the license of that
033    module.  An independent module is a module which is not derived from
034    or based on this library.  If you modify this library, you may extend
035    this exception to your version of the library, but you are not
036    obligated to do so.  If you do not wish to do so, delete this
037    exception statement from your version. */
038    
039    
040    package java.lang.instrument;
041    
042    import 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     */
054    public 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