code: public static Date requireDateParameter (
          HttpServletRequest req, String name, String invalidDataMessage)
          throws DataValidationException
      {
          return parseDateParameter(getParameter(req, name, false), invalidDataMessage);
      }
docs: Fetches the supplied parameter from the request and converts it to a date. The value of the
  parameter should be a date formatted like so: 2001-12-25. If the parameter does not exist or
  is not a well-formed date, a data validation exception is thrown with the supplied message.