Java - Instrumenting with proxies

Using the InvocationHandler interface one can create a simple, yet sophisticated, means of instrumenting a class to obtain statistics about its usage:

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.InvocationTargetException;

public class MyProxy implements InvocationHandler {

private Object _target;
public Object getTarget() { return _target; }
public void setTarget(Object target) { _target = target; }

public MyProxy(Object target) {
_target = target;
} // constructor

public Object invoke(Object proxy,
Method method,
Object[] args)
throws Throwable {

Object result = null;

long start = System.currentTimeMillis();

try {
result = method.invoke(_target, args);
} catch (InvocationTargetException ite) {
long stop = System.currentTimeMillis();
// log the exception here

throw ite.getCause();
}

long stop = System.currentTimeMillis();
// log the invokation results
// (_target, method, stop - start);

return result;
} // invoke()

public static Object createProxy(Object target) {
Object result = target;

Class targetClass = target.getClass();
result = Proxy.newProxyInstance(
targetClass.getClassLoader(),
targetClass.getInterfaces(),
new MyProxy(target)
);


return result;
} // createProxy()

} // class MyProxy