public static void timestamp2Date() {
  long timeMillis = System.currentTimeMillis();
  Date date = new Date(timeMillis);
}

public static void date2Timestamp() {
  Date date = new Date();
  long timeMillis = date.getTime();
}

public static void timestamp2LocalDateTime() {
  long timeMillis = System.currentTimeMillis();
  ZoneId zoneId = ZoneId.systemDefault();
  LocalDateTime localDateTime = Instant.ofEpochMilli(timeMillis).atZone(zoneId).toLocalDateTime();
}

public static void localDateTime2Timestamp() {
  ZoneId zoneId = ZoneId.systemDefault();
  LocalDateTime now = LocalDateTime.now();
  long epochMilli = now.atZone(zoneId).toInstant().toEpochMilli();
}