code: long getYearMonthDayMillis(int year, int month, int dayOfMonth) {
          long millis = getYearMillis(year);
          millis += getTotalMillisByYearMonth(year, month);
          return millis + (dayOfMonth - 1) * (long)DateTimeConstants.MILLIS_PER_DAY;
      }
docs: Get the milliseconds for a particular date.
  
  @param year The year to use.
  @param month The month to use
  @param dayOfMonth The day of the month to use
  @return millis from 1970-01-01T00:00:00Z