从纪元开始获取天数

Question

我想计算从纪元 (1970-01-01) 开始的天数。我试过 joda-time

try {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    Date date1 = sdf.parse("2013-05-03 07:00:00");
    Date date2 = sdf.parse("2013-05-03 23:30:00");


    MutableDateTime epoch = new MutableDateTime();
    epoch.setDate(0); //Set to Epoch time
    System.out.println("Epoch: " + epoch);
    Days days1 = Days.daysBetween(epoch, new MutableDateTime(date1.getTime()));
    Days days2 = Days.daysBetween(epoch, new MutableDateTime(date2.getTime()));
    System.out.println("1) Days Since Epoch: " + days1.getDays());
    System.out.println("2) Days Since Epoch: " + days2.getDays());
} catch (ParseException e) {
    e.printStackTrace(); 
}

并使用逻辑：

// Create Calendar instance
    Calendar calendar1 = Calendar.getInstance();
    Calendar calendar2 = Calendar.getInstance();
    calendar2.setTime(date);
    // Set the values for the calendar fields YEAR, MONTH, and DAY_OF_MONTH.

// calendar1.set(calendar1.YEAR, calendar1.MONTH, Calendar.DAY_OF_MONTH); calendar1.set(1970, 1, 1);

    /*
     * Use getTimeInMillis() method to get the Calendar's time value in
     * milliseconds. This method returns the current time as UTC
     * milliseconds from the epoch
     */
    long miliSecondForDate1 = calendar1.getTimeInMillis();
    long miliSecondForDate2 = calendar2.getTimeInMillis();

    // Calculate the difference in millisecond between two dates
    long diffInMilis = miliSecondForDate2 - miliSecondForDate1;

    /*
     * Now we have difference between two date in form of millsecond we can
     * easily convert it Minute / Hour / Days by dividing the difference
     * with appropriate value. 1 Second : 1000 milisecond 1 Hour : 60 * 1000
     * millisecond 1 Day : 24 * 60 * 1000 milisecond
     */

    long diffInSecond = diffInMilis / 1000;
    long diffInMinute = diffInMilis / (60 * 1000);
    long diffInHour = diffInMilis / (60 * 60 * 1000);
    long diffInDays = diffInMilis / (24 * 60 * 60 * 1000);
    if(logger.isInfoEnabled()) {
        logger.info("Difference in Seconds : " + diffInSecond);
        logger.info("Difference in Minute : " + diffInMinute);
        logger.info("Difference in Hours : " + diffInHour);
        logger.info("Difference in Days : " + diffInDays);
    }

我得到了这两个的不同结果。有人可以帮助我哪里错了。

谢谢。

Answer 1

17006 和 17007 相差 1 天。这种差异很可能来自您所在时区的 7:00 和 23:30 在其他时区的不同日期，例如 UTC。或者反过来，UTC 中的那些时间恰好在您所在时区的不同日期。因此计数减一。我不了解JodaTime，所以我不能给你准确的细节。

16975 和 17006 之间相差 31 天或整月。我可以告诉你这是从哪里来的。 Calendar 月份是从 0 开始的：1 月是 0 月，2 月是 1 月，等等。所以 calendar1.set(1970, 1, 1) 将您的日历设置为 February 1, 1970，31 天后时代。请改用 calendar1.set(1970, Calendar.JANUARY, 1)。您还需要控制 Calendar 的小时、分钟和秒。您可以在 set() 之前致电 clear() 以确保时间是午夜。

如果你可以使用Java8，你可以这样做：

    DateTimeFormatter format = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss");
    OffsetDateTime t1 = LocalDateTime.parse("2013-05-03 07:00:00", format)
            .atOffset(ZoneOffset.UTC);
    OffsetDateTime t2 = LocalDateTime.parse("2013-05-03 23:30:00", format)
            .atOffset(ZoneOffset.UTC);

    System.out.println("1) Days Since Epoch: " + ChronoUnit.DAYS.between(Instant.EPOCH, t1));
    System.out.println("2) Days Since Epoch: " + ChronoUnit.DAYS.between(Instant.EPOCH, t2));

这会打印：

1) Days Since Epoch: 15828
2) Days Since Epoch: 15828

如果您想使用不同的时区：

    DateTimeFormatter format = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss");
    ZonedDateTime t1 = LocalDateTime.parse("2013-05-03 07:00:00", format)
            .atZone(ZoneId.systemDefault());
    ZonedDateTime t2 = LocalDateTime.parse("2013-05-03 23:30:00", format)
            .atZone(ZoneId.systemDefault());

    System.out.println("1) Days Since Epoch: " + ChronoUnit.DAYS.between(Instant.EPOCH, t1));
    System.out.println("2) Days Since Epoch: " + ChronoUnit.DAYS.between(Instant.EPOCH, t2));

您可以填写所需的时区而不是ZoneId.systemDefault()。

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