Investigate the difference between JDK and Spark's time zone offset calculation

  private[sql] def getOffsetFromLocalMillis(millisLocal: Long, tz: TimeZone): Long = {
    var guess = tz.getRawOffset
    // the actual offset should be calculated based on milliseconds in UTC
    val offset = tz.getOffset(millisLocal - guess)
    if (offset != guess) {
      guess = tz.getOffset(millisLocal - offset)
      if (guess != offset) {
        // fallback to do the reverse lookup using java.sql.Timestamp
        // this should only happen near the start or end of DST
        val days = Math.floor(millisLocal.toDouble / MILLIS_PER_DAY).toInt
        val year = getYear(days)
        val month = getMonth(days)
        val day = getDayOfMonth(days)

        var millisOfDay = (millisLocal % MILLIS_PER_DAY).toInt
        if (millisOfDay < 0) {
          millisOfDay += MILLIS_PER_DAY.toInt
        }
        val seconds = (millisOfDay / 1000L).toInt
        val hh = seconds / 3600
        val mm = seconds / 60 % 60
        val ss = seconds % 60
        val ms = millisOfDay % 1000
        val calendar = Calendar.getInstance(tz)
        calendar.set(year, month - 1, day, hh, mm, ss)
        calendar.set(Calendar.MILLISECOND, ms)
        guess = (millisLocal - calendar.getTimeInMillis()).toInt
      }
    }
    guess
  }

            if (zone instanceof ZoneInfo) {
                ((ZoneInfo)zone).getOffsetsByWall(millis, zoneOffsets);
            } else {
                int gmtOffset = isFieldSet(fieldMask, ZONE_OFFSET) ?
                                    internalGet(ZONE_OFFSET) : zone.getRawOffset();
                zone.getOffsets(millis - gmtOffset, zoneOffsets);
            }