incomplete Object information when serialize object with Gson

    @PostMapping("/message/send?access_token={access_token}")
    MessageResponseDTO send(@RequestParam("access_token") String accessToken, @RequestBody AbsMessage message);

Such as the code, I need to call it,the interface has different performance depends on the Object passed. However AbsMessage is a abstract class,when I call it need to pass an object which instance of AbsMessage. But the reuest body doesn't conatin any field from the runtime sub class whic I passed. All fields are from the abstract class. I find the cause at last.

  GsonEncoder#encode(Object object, Type bodyType, RequestTemplate template)
  @Override
  public void encode(Object object, Type bodyType, RequestTemplate template) {
    template.body(gson.toJson(object, bodyType));
  }

It serializes object with the type which declared in the function,not runtime type of the passed object. If gson.toJson(object),It appears normal.