javassist.tools.reflect

(also recently known as interceptors or AOP?)

This package enables a metaobject to trap method calls and field accesses on a regular Java object. It provides a class Reflection, which is a main module for implementing runtime behavioral reflection. It also provides a class Loader and Compiler as utilities for dynamically or statically translating a regular class into a reflective class.

An instance of the reflective class is associated with a runtime metaobject and a runtime class metaobject, which control the behavior of that instance. The runtime metaobject is created for every (base-level) instance but the runtime class metaobject is created for every (base-level) class. Metaobject is the root class of the runtime metaobject and ClassMetaobject is the root class of the runtime class metaobject.

This package is provided as a sample implementation of the reflection mechanism with Javassist. All the programs in this package uses only the regular Javassist API; they never call any hidden methods.

The most significant class in this package is Reflection. See the description of this class first.

A ClassMetaobject is created for every class of reflective objects.

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.

A Metaobject is created for every object at the base level.

If a class is reflective, then all the method invocations on every instance of that class are intercepted by the runtime metaobject controlling that instance.