java 1.8 時間戳localdatetime轉換

java 1.8 中 關於LocalDateTime 的與long 的轉換，在1.8 localdateTime 中對於時區設置是敏感的，這個須要留意

public static void main(String[] args) {
    Period sixMonths = Period.ofMonths(1);
    LocalDate date = LocalDate.now();
    LocalDate future = date.minus(sixMonths);
    System.out.println(future);
    LocalDateTime d =
            LocalDateTime.ofInstant(Instant.ofEpochMilli(System.currentTimeMillis()), ZoneId.systemDefault());

    System.out.println(d.minus(sixMonths).atZone(ZoneId.systemDefault()).toInstant().toEpochMilli());
    ZoneId zoneId = ZoneId.systemDefault(); // or: ZoneId.of("Europe/Oslo");
    long epoch = date.atStartOfDay(zoneId).toEpochSecond();
    System.out.println(epoch);
    System.out.println(new Date(1490585496969l));
    System.out.println(ZoneId.systemDefault());
    Set<String> set = new HashSet<>();
    if (set.isEmpty()){
        System.out.println("true");
    }
}