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.
| License file (Also see the copyright notices below) | |
| Tutorial | |
| The Javassist jar file (class files) | |
| The source files | |
| The top page of the Javassist API document. | |
| Sample programs |
To extract source files from the archive, use the jar command:
% jar xvf javassist-src.zip
JDK 1.2.2 or later is needed.
In the description below, we assume that the platform is JDK 1.2 (or later) for Solaris. If the platform is JDK 1.2 (or later) for Windows, the class-path option is:
-classpath ".;javassist.jar"
If you don't want to put the class-path option, copy ./javassist.jar to
<java-home> depends on the system. It is usually /usr/local/java, c:\jdk1.2\, etc.
If you don't use javassist.jar, first compile Javassist:
% cd src % javac -d .. javassist/*.java javassist/*/*.java % cd ..
Then you can compile and run the sample programs without the class-path option.
This is a very simple program using Javassist.
To run, type the commands:
% javac -classpath ".:javassist.jar" sample/Test.java % java -cp ".:javassist.jar" sample.Test
For more details, see sample/Test.java
This is the "verbose metaobject" example well known in reflective programming. This program dynamically attaches a metaobject to a Person object. The metaobject prints a message if a method is called on the Person object.
To run, type the commands:
% javac -classpath ".:javassist.jar" sample/reflect/*.java % java -cp ".:javassist.jar" javassist.reflect.Loader sample.reflect.Main Joe
Compare this result with that of the regular execution without reflection:
% java -cp ".:javassist.jar" sample.reflect.Person Joe
For more details, see sample/reflect/Main.java
Furthermore, the Person class can be statically modified so that all the Person objects become reflective without sample.reflect.Main. To do this, type the commands:
% java -cp ".:javassist.jar" javassist.reflect.Compiler sample.reflect.Person -m sample.reflect.VerboseMetaobj
Then,
% java -cp ".:javassist.jar" sample.reflect.Person Joe
This is another example of reflective programming.
To run, type the commands:
% javac -classpath ".:javassist.jar" sample/duplicate/*.java % java -cp ".:javassist.jar" sample.duplicate.Main
Compare this result with that of the regular execution without reflection:
% java sample.duplicate.Viewer
For more details, see sample/duplicate/Main.java
This example shows the use of Javassit for producing a class representing a vector of a given type at compile time. This is a demonstration of the use of javassist.preproc package.
To run, type the commands:
% javac -classpath ".:javassist.jar" sample/vector/*.java % java -cp ".:javassist.jar" javassist.preproc.Compiler sample/vector/Test.j % javac sample/vector/Test.java % java sample.vector.Test
For more details, see sample/vector/Test.j and sample/vector/VectorAssistant.java
This demonstrates the javassist.rmi package.
To run, type the commands:
% javac -classpath ".:javassist.jar" sample/rmi/*.java % java -cp ".:javassist.jar" sample.rmi.Counter 5001
The second line starts a web server listening to port 5001.
Then, open sample/rmi/webdemo.html with a web browser running on the local host. (webdemo.html trys to fetch an applet from http://localhost:5001/, which is the web server we started above.)
Otherwise, run sample.rmi.CountApplet as an application:
% java -cp ".:javassist.jar" javassist.web.Viewer localhost 5001 sample.rmi.CountApplet
This is a demonstration of the class evolution mechanism implemented with Javassist. This mechanism enables a Java program to reload an existing class file under some restriction.
To run, type the commands:
% javac -classpath ".:javassist.jar" sample/evolve/*.java % java -cp ".:javassist.jar" sample.evolve.DemoLoader 5003
The second line starts a class loader DemoLoader, which runs a web server DemoServer listening to port 5003.
Then, open http://localhost:5003/demo.html with a web browser running on the local host. (Or, see sample/evolve/start.html.)
Javassist provides a class file viewer for debugging. For more details, see javassist.Dump.
- version 2.5 in May, 2003.
From this version, Javassist is part of the JBoss project.
- version 2.4 in February, 2003.
- version 2.3 in December, 2002.
- version 2.2 in October, 2002.
javassist.expr has been added.
This is replacement of classic CodeConverter.
- version 2.1 in July, 2002.
- version 2.0 (major update) in November, 2001.
version 1.0 in July, 2001.
- version 0.8
- version 0.7
- version 0.6
- version 0.5
- version 0.4
- version 0.3
- version 0.2
-version 0.1 in April, 1999.
Javassist, a Java-bytecode translator toolkit.
The contents of this software, Javassist, are subject to
the Mozilla Public License Version 1.1 (the "License"); Software distributed under the License is distributed on an "AS IS"
basis, WITHOUT WARRANTY OF The Original Code is Javassist.
The Initial Developer of the Original Code is Shigeru Chiba.
Portions created by the Initial Developer are Contributor(s): ______________________________________.
Alternatively, the contents of this software may be used under the
terms of the GNU Lesser General Public License Version 2.1 or later
(the "LGPL"), in which case the provisions of the LGPL are applicable
instead of those above. If you wish to allow use of your version of
this software only under the terms of the LGPL, and not to allow others to
use your version of this software under the terms of the MPL, indicate
your decision by deleting the provisions above and replace them with
the notice and other provisions required by the LGPL. If you do not
delete the provisions above, a recipient may use your version of this
software under the terms of either the MPL or the LGPL.
If you obtain this software as part of JBoss, the contents of this
software may be used under only the terms of the LGPL. To use them
under the MPL, you must obtain a separate package including only
Javassist but not the other part of JBoss.
All the contributors to the original source tree must agree to
the original license term described above.
The development of this software is sponsored in part by the PRESTO
programs of Japan
Science and Technology Corporation.
I'd like to thank Michiaki Tatsubori, Johan Cloetens,
Philip Tomlinson, Alex Villazon, Pascal Rapicault, Dan HE, Eric Tanter,
Michael Haupt, Toshiyuki Sasaki, Renaud Pawlak, Luc Bourlier,
Eric Bui, Lewis Stiller, Susumu Yamazaki, Rodrigo Teruo Tomita,
Marc Segura-Devillechaise, Jan Baudisch, Julien Blass, Yoshiki Sato,
Fabian Crabus, Bo Norregaard Jorgensen, Bob Lee, Bill Burke,
Remy Sanlaville, Muga Nishizawa, Alexey Loubyansky, Saori Oki,
Andreas Salathe, Dante Torres estrada, S. Pam, Nuno Santos,
Denis Taye, and Colin Sampaleanu
for their contributions.
Copyright notices
Copyright (C) 1999-2003 Shigeru Chiba. All Rights Reserved.
you may not use this software except in compliance
with the License. You may obtain a copy of the License at
http://www.mozilla.org/MPL/
ANY KIND, either express or implied.
See the License for the specific language governing rights and
limitations under the License.
Copyright (C) 1999-2003 Shigeru Chiba. All Rights Reserved.
Acknowledgments
Shigeru Chiba
(Email: chiba@acm.org)
Dept. of Math. and Computing Sciences,
Tokyo Institute of Technology