Java GregorianCalendar 和 DST 转换时间

Question

我有一个 GregorianCalendar，我正在尝试设置时间。我从一个日历中获取日期，从另一日历中获取时间。除了 DST 切换日的凌晨 2 点外，它大部分时间都有效。

例如，日期为 3/10/2013、时间为 2:40AM、目标输出为 3/10/2013 2:40AM，我得到 3/10/2013 3:40AM:

GregorianCalendar reportingDate = //some instance with a relevant date (in this case 3/10/2013)
GregorianCalendar targetTime = //some instance with a relevant time (in this case 2:40AM)
Calendar combination = Calendar.getInstance();
combination.set(Calendar.YEAR, reportingDate.get(Calendar.YEAR));
combination.set(Calendar.MONTH, reportingDate.get(Calendar.MONTH));
combination.set(Calendar.DAY_OF_YEAR, reportingDate.get(Calendar.DAY_OF_YEAR));
combination.set(Calendar.HOUR, targetTime.get(Calendar.HOUR));
combination.set(Calendar.AM_PM, targetTime.get(Calendar.AM_PM));
combination.set(Calendar.MINUTE, targetTime.get(Calendar.MINUTE));
combination.set(Calendar.SECOND, targetTime.get(Calendar.SECOND));

一旦代码在组合日历上设置 AM_PM，时间就会切换到凌晨 3:40。我希望它不要切换。我认为这与目标时间日历被创建为纪元日期上的时间有关，但我希望目标时间的具体日期并不重要......

Answer 1

基于这个输出...我认为这就是 Java 处理 DST 的方式？好像凌晨 2-3 点就被遗忘了

请参阅下面我的评论

final Calendar reportingDate = Calendar.getInstance();
reportingDate.set(Calendar.YEAR, 2013);
reportingDate.set(Calendar.MONTH, Calendar.MARCH);
reportingDate.set(Calendar.DAY_OF_MONTH, 10);

final Calendar targetTime = Calendar.getInstance();
targetTime.set(Calendar.AM_PM, Calendar.AM);
targetTime.set(Calendar.HOUR_OF_DAY, 3);
targetTime.set(Calendar.MINUTE, 0);
targetTime.set(Calendar.SECOND, 0);
targetTime.set(Calendar.MILLISECOND, 0);

final Calendar combination = Calendar.getInstance();
combination.set(Calendar.YEAR, reportingDate.get(Calendar.YEAR));
combination.set(Calendar.MONTH, reportingDate.get(Calendar.MONTH));
combination.set(Calendar.DAY_OF_YEAR, reportingDate.get(Calendar.DAY_OF_YEAR));
combination.set(Calendar.HOUR, targetTime.get(Calendar.HOUR));
combination.set(Calendar.AM_PM, targetTime.get(Calendar.AM_PM));
combination.set(Calendar.MINUTE, targetTime.get(Calendar.MINUTE));
combination.set(Calendar.SECOND, targetTime.get(Calendar.SECOND));
combination.set(Calendar.MILLISECOND, targetTime.get(Calendar.MILLISECOND));

final long timeAtCombined = combination.getTimeInMillis();

final SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy HH:mm:ss.SSSZ");
sdf.setTimeZone(TimeZone.getTimeZone("US/Eastern"));

// subtract one minute
System.out.println(sdf.format(combination.getTime()));
combination.add(Calendar.MILLISECOND, -1);
System.out.println(sdf.format(combination.getTime()));

// millis @ 3
System.out.println(sdf.format(new Date(timeAtCombined)));
// millis @ 3 - 1ms
System.out.println(sdf.format(new Date(timeAtCombined - 1)));

输出

03/10/2013 03:00:00.000-0400
03/10/2013 01:59:59.999-0500
03/10/2013 03:00:00.000-0400
03/10/2013 01:59:59.999-0500