code: public String date (String format, Object arg)
      {
          Date when = massageDate(arg);
          if (when == null) {
              return format;
          }
          SimpleDateFormat fmt = new SimpleDateFormat(format, getLocale());
          return fmt.format(when);
      }
docs: Uses {@link SimpleDateFormat} to translate the supplied {@link
  Long} or {@link Date} argument into a formatted date string using
  the locale appropriate to the current request.