private static long unixTimestamp(
      int year, int month, int day, int hour, int minute, int second, int mills) {
    final int date = ymdToUnixDate(year, month, day);
    return (long) date * MILLIS_PER_DAY
        + (long) hour * MILLIS_PER_HOUR
        + (long) minute * MILLIS_PER_MINUTE
        + (long) second * MILLIS_PER_SECOND
        + mills;
  }
Convert unix timestamp (seconds since '1970-01-01 00:00:00' UTC) to datetime string in the
given format.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/util/DateTimeUtils.java