Code Quality Rank: L2
Programming language: Java
License: GNU General Public License v3.0 or later

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Java bytecode engineering toolkit

Javassist version 3

Copyright (C) 1999-2021 by Shigeru Chiba, All rights reserved.

Javassist (JAVA programming ASSISTant) makes Java bytecode manipulation simple. It is a class library for editing bytecodes in Java; it enables Java programs to define a new class at runtime and to modify a class file when the JVM loads it. Unlike other similar bytecode editors, Javassist provides two levels of API: source level and bytecode level. If the users use the source- level API, they can edit a class file without knowledge of the specifications of the Java bytecode. The whole API is designed with only the vocabulary of the Java language. You can even specify inserted bytecode in the form of source text; Javassist compiles it on the fly. On the other hand, the bytecode-level API allows the users to directly edit a class file as other editors.

This software is distributed under the Mozilla Public License Version 1.1, the GNU Lesser General Public License Version 2.1 or later, or the Apache License Version 2.0.


  • [Readme.html](Readme.html) Readme file (a longer version of this file).

  • [License.html](License.html) License file

  • [tutorial/tutorial.html](tutorial/tutorial.html) Tutorial

  • ./javassist.jar The Javassist jar file (class files)

  • ./src/main The source files

  • [html/index.html](html/index.html) The top page of the Javassist API document.

*Note that all licence references and agreements mentioned in the Javassist README section above are relevant to that project's source code only.