Dynamic implementation for interface/abstract class in Java

What's the de-facto solution for building dynamic implementation of interfaces and/or abstract classes? What I basically want is:

interface IMyEntity {
  int getValue1();
  void setValue1(int x);
}
...
class MyEntityDispatcher implements WhateverDispatcher {
  public Object handleCall(String methodName, Object[] args) {
     if(methodName.equals("getValue1")) {
       return new Integer(123);
     } else if(methodName.equals("setValue")) {
       ...
     }
     ...
  }
}
...
IMyEntity entity = Whatever.Implement<IMyEntity>(new MyEntityDispatcher());
entity.getValue1(); // returns 123