code: public ResponseWrapper retractMessage(String username, long messageId)
              throws APIConnectionException, APIRequestException {
          StringUtils.checkUsername(username);
          return _httpClient.sendPost(_baseUrl + messagePath + "/" + username + "/" + messageId + "/retract", null);
      }
docs: retract message
  消息撤回
  @param username 用户名
  @param messageId message id
  @return No Content， Error Code：
  855001 out of retract message time, the effective time is within 3 minutes after sending message
  855003 the retract message is not exist
  855004 the message had been retracted
  @throws APIConnectionException connect exception
  @throws APIRequestException request exception