code: public static String requireParameter (
          HttpServletRequest req, String name, String missingDataMessage)
          throws DataValidationException
      {
          String value = getParameter(req, name, true);
          if (StringUtil.isBlank(value)) {
              throw new DataValidationException(missingDataMessage);
          }
          return value;
      }
docs: Fetches the supplied parameter from the request. If the parameter does not exist, a data
  validation exception is thrown with the supplied message.