code: public void setInvocationHandler(Object proxy, InvocationHandler handler) {
          Field field = getInvocationHandlerField();
          try {
              field.set(proxy, handler);
          } catch (IllegalArgumentException e) {
              throw new RuntimeException(e);
          } catch (IllegalAccessException e) {
              throw new RuntimeException(e);
          }
      }
docs: Sets the invocation handler for a proxy created from this factory.
  
  @param proxy the proxy to modify
  @param handler the handler to use