public Class Loader

To run a program, say MyApp, including a reflective class, you must write a start-up program as follows:

public class Main {
  public static void main(String[] args) throws Throwable {
    javassist.tools.reflect.Loader cl
        = (javassist.tools.reflect.Loader)Main.class.getClassLoader();
    cl.makeReflective("Person", "MyMetaobject",
                      "javassist.tools.reflect.ClassMetaobject");
    cl.run("MyApp", args);
  }
}

Then run this program as follows:

% java javassist.tools.reflect.Loader Main arg1, ...

This command runs Main.main() with arg1, ... and Main.main() runs MyApp.main() with arg1, ... The Person class is modified to be a reflective class. Method calls on a Person object are intercepted by an instance of MyMetaobject.

Also, you can run MyApp in a slightly different way:

public class Main2 {
  public static void main(String[] args) throws Throwable {
    javassist.tools.reflect.Loader cl = new javassist.tools.reflect.Loader();
    cl.makeReflective("Person", "MyMetaobject",
                      "javassist.tools.reflect.ClassMetaobject");
    cl.run("MyApp", args);
  }
}

This program is run as follows:

% java Main2 arg1, ...

The difference from the former one is that the class Main is loaded by javassist.tools.reflect.Loader whereas the class Main2 is not. Thus, Main belongs to the same name space (security domain) as MyApp whereas Main2 does not; Main2 belongs to the same name space as javassist.tools.reflect.Loader. For more details, see the notes in the manual page of javassist.Loader.

The class Main2 is equivalent to this class:

public class Main3 {
  public static void main(String[] args) throws Throwable {
    Reflection reflection = new Reflection();
    javassist.Loader cl
        = new javassist.Loader(ClassPool.getDefault(reflection));
    reflection.makeReflective("Person", "MyMetaobject",
                              "javassist.tools.reflect.ClassMetaobject");
    cl.run("MyApp", args);
  }
}

Note:

javassist.tools.reflect.Loader does not make a class reflective if that class is in a java.* or javax.* pacakge because of the specifications on the class loading algorithm of Java. The JVM does not allow to load such a system class with a user class loader.

To avoid this limitation, those classes should be statically modified with javassist.tools.reflect.Compiler and the original class files should be replaced.