Javassist

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.

Aspect Oriented Programming: Javassist can be a good tool for adding new methods into a class and for inserting before/after/around advice at the both caller and callee sides.

Reflection: One of applications of Javassist is runtime reflection; Javassist enables Java programs to use a metaobject that controls method calls on base-level objects. No specialized compiler or virtual machine are needed.

We have started developing a light-weight but powerful AOP framework on top of Javassist.
Please visit our GluonJ site.

• Binaries, sources, samples, API manual, and tutorial. (zip)
• Online API manual (HTML format)
• Tutorial (HTML format) 
  (Japanese translation of the tutorial for version 3.0 is here)

• The Latest Snapshot

  available from GitHub.

• Old source code (3.17.1.GA or before)

  The source code is available from FishEye or Subversion:

  svn co http://anonsvn.jboss.org/repos/javassist/trunk
  

  This command will create the ./trunk direcotry.

  To build the downloaded source files, use ant:

  cd trunk	# move to the source directory
  ant jar         # build javassist.jar
  ant javadocs    # build API reference
  

  For more details, see build.xml.

Join our discussion forums:

• Bug Tracker

• Discussion Forums [ Users ] [ Developers ]

• Articles:
  • Javassist: Java Bytecode Engineering Made Simple
    by Shigeru Chiba, Java Developer's Journal, vol. 9, issue 1, January 8, 2004.

  • Java programming dynamics, Part 4: Class transformation with Javassist
    by Dennis M. Sosnoski, IBM developerWorks, September 16, 2003.
    Java programming dynamics, Part 5: Transforming classes on-the-fly
    by Dennis M. Sosnoski, IBM developerWorks, February 3, 2004.
    Java programming dynamics, Part 6: Aspect-oriented changes with Javassist
    by Dennis M. Sosnoski, IBM developerWorks, March 2, 2004.

An Easy-to-Use Toolkit for Efficient Java Bytecode Translators

Shigeru Chiba and Muga Nishizawa
Proc. of 2nd Int'l Conf. on Generative Programming and Component Engineering (GPCE '03),
LNCS 2830, pp.364-376, Springer-Verlag, 2003.
(The performance of Javassist)

Using HotSwap for Implementing Dynamic AOP Systems

Shigeru Chiba, Yoshiki Sato, and Michiaki Tatsubori
ECOOP'03 Workshop on Advancing the State of the Art in Runtime Inspection (ASARTI), July 21st, 2003.
(Dynamic AOP, An Application of Javassist)

AOP in the Academia

Shigeru Chiba, JBossTwo AOP Panel, June 2003.

A Bytecode Translator for Distributed Execution of "Legacy" Java Software

Michiaki Tatsubori, Toshiyuki Sasaki, Shigeru Chiba and Kozo Itano
ECOOP 2001 -- Object-Oriented Programming, LNCS 2072, Springer Verlag, pp.236-255, 2001.
(An application of Javassist)

Load-time Structural Reflection in Java

Shigeru Chiba
ECOOP 2000 -- Object-Oriented Programming, LNCS 1850, Springer Verlag, page 313-336, 2000.
(The overview of Javassist)

Javassist --- A Reflection-based Programming Wizard for Java
Shigeru Chiba
In Proceedings of the ACM OOPSLA'98 Workshop on Reflective Programming in C++ and Java October, 1998.
(An very early sketch of the design of Javassist)

We are developing other reflective systems for C++ and Java.

OpenC++
An extensible C++ preprocessor based on compile-time reflection.

OJ
An extensible Java preprocessor based on compile-time reflection.

Javassist version 2.4 is also available (February 20, 2003)
This version is distributed under the Mozilla Public License 1.1.

• Binaries, sources, samples, and online manuals. (tar+gzip)
• The latest snapshot of the jar file (April 30)

Javassist version 1.0 is also available (July 24, 2001).

• Binaries, sources, samples, and online manuals. (tar+gzip)
• Online manual (HTML format)
• Tutorial (HTML format)
• Bug-fixed source of javassist.reflect package (August 7, 2001).