Question

我希望在两个日期之间获得所有Daylight Saving Time（DST）小时。

这是我的示例代码：

public static void main(String[] args) {

    Date startDate = new Date();
    Calendar startCalendar = Calendar.getInstance();
    startCalendar.setTime(startDate);
    startCalendar.set(2014, 2, 1, 0, 0, 0);
    startCalendar.set(Calendar.MILLISECOND, 0);

    Date endDate = new Date();
    Calendar endCalendar = Calendar.getInstance();
    endCalendar.setTime(endDate);
    endCalendar.set(2014, 2, 31, 0, 0, 0);
    endCalendar.set(Calendar.MILLISECOND, 0);

    DateTime startDateTime = new DateTime(startCalendar);
    DateTime endDateTime = new DateTime(endCalendar).plusDays(1);

    Hours hours = Hours.hoursBetween(startDateTime, endDateTime);

    // actual is 744
    System.out.println("Expected: 743, actual: " + hours.getHours());
}

嗯，我显然错过了一些东西，但我无法发现错误。

Answer 1

主要问题是您未能指定时区。

当我在西雅图运行你的代码时，我在2014年3月的时间里743小时。为什么？因为我的默认时区。在美国西海岸，Daylight Saving Time从2014年3月9日星期日02:00开始。请参阅此页面Time change dates in 2014。那天，第9天，实际上是23小时而不是24小时。

但如果冰岛有人运行完全相同的代码，她会得到744。为什么？因为冰岛人太聪明了，无法忍受夏令时的废话。

另外，作为一个好习惯，你应该在尝试使用几天时调用Joda-Time方法withTimeAtStartOfDay()。以前我们使用过Joda-Time的midnight方法，但是因为某些日历do not have a midnight中的某些日子而被弃用。

提示：请注意以standard命名的Joda-Time方法，文档解释的方法是24小时的假设。换句话说，这些方法忽略了夏令时变换。

以下是Java 7中使用Joda-Time 2.3的一些示例代码。

// © 2013 Basil Bourque. This source code may be used freely forevery by anyone taking full responsibility for doing so.

// Joda-Time - The popular alternative to Sun/Oracle's notoriously bad date, time, and calendar classes bundled with Java 7 and earlier.
// http://www.joda.org/joda-time/

// Joda-Time will become outmoded by the JSR 310 Date and Time API introduced in Java 8.
// JSR 310 was inspired by Joda-Time but is not directly based on it.
// http://jcp.org/en/jsr/detail?id=310

// By default, Joda-Time produces strings in the standard ISO 8601 format.
// https://en.wikipedia.org/wiki/ISO_8601

// Time Zone list: http://joda-time.sourceforge.net/timezones.html
org.joda.time.DateTimeZone seattleTimeZone = org.joda.time.DateTimeZone.forID("America/Los_Angeles");
org.joda.time.DateTimeZone icelandTimeZone = org.joda.time.DateTimeZone.forID("Atlantic/Reykjavik");

// Switch between using 'seattleTimeZone' and 'icelandTimeZone' to see different results (23 vs 24).
org.joda.time.DateTime theNinth = new org.joda.time.DateTime( 2014, 3, 9, 0, 0, seattleTimeZone ) ; // Day when DST begins.
org.joda.time.DateTime theTenth = theNinth.plusDays( 1 ); // Day after DST begins.

// Using "hoursBetween()" method with a pair of DateTimes.
org.joda.time.Hours hoursObject = org.joda.time.Hours.hoursBetween( theNinth.withTimeAtStartOfDay(), theTenth.withTimeAtStartOfDay() );
int hoursInt = hoursObject.getHours();
System.out.println( "Expected 23 from hoursInt, got: " + hoursInt );

// Using an Interval.
org.joda.time.Interval interval = new Interval( theNinth.withTimeAtStartOfDay(), theTenth.withTimeAtStartOfDay() );
System.out.println( "Expected 23 from interval, got: " + org.joda.time.Hours.hoursIn(interval).getHours() );

// Using a Period with Standard days.
org.joda.time.Period period = new org.joda.time.Period( theNinth.withTimeAtStartOfDay(), theTenth.withTimeAtStartOfDay() );
org.joda.time.Hours standardHoursObject = period.toStandardHours();
System.out.println( "Expected 24 from standardHoursObject, got: " + standardHoursObject.getHours() );

Answer 2

欢迎来到日期/时间处理的混乱。你的问题是时区。具体来说，无论您在哪个时区观察夏令时，并且在您的间隔期间发生开关（弹簧向前），这会将其缩短一个小时。请参阅此代码。

public class DateTimeTest {
    public static void main(String[] args) {
    DateTime startDateTime = new DateTime()
        .withYear(2014)
        .withMonthOfYear(3)
        .withDayOfMonth(1)
        .withHourOfDay(0)
        .withMinuteOfHour(0)
        .withSecondOfMinute(0)
        .withMillisOfSecond(0)
        .withZone(DateTimeZone.forID("US/Eastern"));

    DateTime endDateTime = new DateTime()
        .withYear(2014)
        .withMonthOfYear(3)
        .withDayOfMonth(31)
        .withHourOfDay(0)
        .withMinuteOfHour(0)
        .withSecondOfMinute(0)
        .withMillisOfSecond(0)
        .withZone(DateTimeZone.forID("US/Eastern"))
        .plusDays(1);

    System.out.println("Expected 744, got: " 
        + Hours.hoursBetween(startDateTime, endDateTime).getHours());  // 743

    DateTime startUtc = startDateTime.withZoneRetainFields(DateTimeZone.UTC);
    DateTime endUtc = endDateTime.withZoneRetainFields(DateTimeZone.UTC);

    System.out.println("Expected 744, got: " 
        + Hours.hoursBetween(startUtc, endUtc).getHours());  // 744
    }
}

Answer 3

我也想不出来（但是在Joda时间？），但是你可以解决这个问题。毫秒乘以3600000L的差异应该是准确的小时数。我试过了743。

如何在Joda日期之间获得正确的小时数？

3 个答案: