public static long createDate(final Integer year, final Integer month, final Integer day) {
        final ZonedDateTime dateTime = LocalDate.of(year, month, day).atStartOfDay(UTC);
        final long millis = dateTime.toInstant().toEpochMilli();
        return millis;
    }
Create a date in the same way.

@param year  e.g. 2001
@param month e.g. 01
@param day   e.g. 31
stroom-util/src/main/java/stroom/util/PeriodUtil.java