javassist/Examples.md

How to run program examples

JDK 1.4 or later is needed.

0. If you have Apache Ant

Run the sample-all task. Otherwise, follow the instructions below.

1. Move to the directory where this Examples.md file is located.

In the following instructions, we assume that the javassist.jar file is included in the class path. For example, the javac and java commands must receive the following classpath option:

-classpath ".:javassist.jar"

If the operating system is Windows, the path separator must be not : (colon) but ; (semicolon). The java command can receive the -cp option as well as -classpath.

If you don’t want to use the class-path option, you can make javassist.jar included in the CLASSPATH environment:

export CLASSPATH=.:javassist.jar

or if the operating system is Windows:

set CLASSPATH=.;javassist.jar

Otherwise, you can copy javassist.jar to the directory <java-home>/jre/lib/ext.

<java-home> depends on the system. It is usually /usr/local/java or c:\j2sdk1.4\, etc.

2. sample/Test.java

This is a very simple program using Javassist.

To run, type the commands:

% javac sample/Test.java
% java sample.Test

For more details, see sample/Test.java

3. sample/reflect/*.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 sample/reflect/*.java
% java javassist.tools.reflect.Loader sample.reflect.Main Joe

Compare this result with that of the regular execution without reflection:

% java 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 javassist.tools.reflect.Compiler sample.reflect.Person -m sample.reflect.VerboseMetaobj

Then,

% java sample.reflect.Person Joe

4. sample/duplicate/*.java

This is another example of reflective programming. To run, type the commands:

% javac sample/duplicate/*.java
% java 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

5. sample/vector/*.java

This example shows the use of Javassit for producing a class representing a vector of a given type at compile time.

To run, type the commands:

% javac sample/vector/*.java
% java sample.preproc.Compiler sample/vector/Test.j
% javac sample/vector/Test.java
% java sample.vector.Test

Note: javassist.jar is unnecessary to compile and execute sample/vector/Test.java. For more details, see sample/vector/Test.j and sample/vector/VectorAssistant.java.

6. sample/rmi/*.java

This demonstrates the javassist.rmi package. To run, type the commands:

% javac sample/rmi/*.java
% java 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 javassist.web.Viewer localhost 5001 sample.rmi.CountApplet

7. sample/evolve/*.java

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 sample/evolve/*.java
% java 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.)

8. sample/hotswap/*.java

This shows dynamic class reloading by the JPDA. It needs JDK 1.4 or later. To run, first type the following commands:

% cd sample/hotswap
% javac *.java
% cd logging
% javac *.java
% cd ..

If your Java is 1.4, then type:

% java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8000 Test

If you are using Java 5, then type:

% java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=8000 Test

Note that the class path must include JAVA_HOME/lib/tools.jar.