code: @SuppressWarnings("unchecked")
      private void addCallBackMethod(EntityMetadata metadata, Class<?> jpaAnnotation, CallbackMethod callbackMethod)
      {
          Map<Class<?>, List<? extends CallbackMethod>> callBackMethodsMap = metadata.getCallbackMethodsMap();
          List<CallbackMethod> list = (List<CallbackMethod>) callBackMethodsMap.get(jpaAnnotation);
          if (null == list)
          {
              list = new ArrayList<CallbackMethod>();
              callBackMethodsMap.put(jpaAnnotation, list);
          }
          list.add(callbackMethod);
      }
docs: Adds the call back method.
  
  @param metadata
  the metadata
  @param jpaAnnotation
  the jpa annotation
  @param callbackMethod
  the callback method