http://www.javassist.org/: Javassist (JAVA programming ASSISTant) makes Java bytecode manipulation simple. It is a class library for editing bytecodes in Java. (Shigeru Chiba, www.javassist.org) 
/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later,
 * or the Apache License Version 2.0.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */

package javassist;


An observer of Loader.
The users can define a class implementing this
interface and attach an instance of that class to a
Loader object so that it can translate a class file
when the class file is loaded into the JVM.

See Also:
  • addTranslator.addTranslator(ClassPool, Translator)
/**
 * An observer of <code>Loader</code>.
 * The users can define a class implementing this
 * interface and attach an instance of that class to a
 * <code>Loader</code> object so that it can translate a class file
 * when the class file is loaded into the JVM.
 *
 * @see Loader#addTranslator(ClassPool, Translator)
 */
public interface Translator {
    
Is invoked by a Loader for initialization
when the object is attached to the Loader object.
This method can be used for getting (for caching) some
CtClass objects that will be accessed
in onLoad() in Translator.

Params:
  • pool –      the ClassPool that this translator
                         should use.
Throws:
See Also:
/**
     * Is invoked by a <code>Loader</code> for initialization
     * when the object is attached to the <code>Loader</code> object.
     * This method can be used for getting (for caching) some
     * <code>CtClass</code> objects that will be accessed
     * in <code>onLoad()</code> in <code>Translator</code>.
     *
     * @param pool      the <code>ClassPool</code> that this translator
     *                          should use.
     * @see Loader
     * @throws NotFoundException    if a <code>CtClass</code> cannot be found.
     * @throws CannotCompileException   if the initialization by this method
     *                                  fails.
     */
    void start(ClassPool pool)
        throws NotFoundException, CannotCompileException;

    
Is invoked by a Loader for notifying that
a class is loaded.  The Loader calls

pool.get(classname).toBytecode()

to read the class file after onLoad() returns.

classname may be the name of a class
that has not been created yet.
If so, onLoad() must create that class so that
the Loader can read it after onLoad()
returns.

Params:
  • pool –      the ClassPool that this translator
                         should use.
  • classname –     the name of the class being loaded.
Throws:
See Also:
/**
     * Is invoked by a <code>Loader</code> for notifying that
     * a class is loaded.  The <code>Loader</code> calls
     *
     * <pre>
     * pool.get(classname).toBytecode()</pre>
     *
     * to read the class file after <code>onLoad()</code> returns.
     *
     * <p><code>classname</code> may be the name of a class
     * that has not been created yet.
     * If so, <code>onLoad()</code> must create that class so that
     * the <code>Loader</code> can read it after <code>onLoad()</code>
     * returns.
     *
     * @param pool      the <code>ClassPool</code> that this translator
     *                          should use.
     * @param classname     the name of the class being loaded.
     * @see Loader
     * @throws NotFoundException    if a <code>CtClass</code> cannot be found.
     * @throws CannotCompileException   if the code transformation
     *                                  by this method fails.
     */
    void onLoad(ClassPool pool, String classname)
        throws NotFoundException, CannotCompileException;
}