Java中的自定义ZoneIds/Time Zones

Question

我正在尝试使用Java的ZoneId和ZoneOffsetTransitionRule对iCalendarVTIMEZONE对象进行建模。

我的VTIMEZONE对象看起来像

BEGIN:VTIMEZONE
TZID:Central European Standard Time
BEGIN:STANDARD
DTSTART:16010101T030000
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
RRULE:FREQ=YEARLY;INTERVAL=1;BYDAY=-1SU;BYMONTH=10
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:16010101T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
RRULE:FREQ=YEARLY;INTERVAL=1;BYMONTH=1;BYDAY=MO
END:DAYLIGHT
END:VTIMEZONE

我需要创建自己的ZoneId来对此进行建模，因为据我所知，没有具有这些偏移的ZoneId，夏令时从1月的第一个星期一开始(而不是3月的某个星期日(。

我有以下内容用于创建ZoneOffsetTransitionRule

ZoneOffsetTransitionRule of =
ZoneOffsetTransitionRule.of(Month.JANUARY, 1, DayOfWeek.MONDAY, LocalTime.of(2, 0),
false, ZoneOffsetTransitionRule.TimeDefinition.STANDARD, ZoneOffset.ofHours(1),
ZoneOffset.ofHours(1), ZoneOffset.ofHours(2));

但我不确定它是否正确，也不确定如何从中创建ZoneId。

• 这个转换规则对我的VTIMEZONE的DAYLIGHT组件建模准确吗
• 如何创建ZoneId，以便最终创建ZonedDateTime

Answer 1

获得ZoneId的唯一方法(至少如果我们不是非常熟练的话(是通过ZoneId及其子类ZoneOffset的工厂方法。起初，这可能会留下内置的ZoneIds。然而，有一个后门可以指定ZoneId.of可以产生的额外ZoneIds。它被称为ZoneRulesProvider。我们需要指定一个新的唯一ID，并且需要指定区域规则(因此名称为ZoneRulesProvider(。

所以有了你的ZoneOffsetTransitionRule，你已经在路上了。不过，我们需要其中两个，一个用于过渡到夏令时(通常发生在春季(，另一个用于在秋季转向另一个方向。

当然，下面的清单不是生产代码，只是为了证明开发和注册自己的ZoneRulesProvider是可行的。

final String customZoneId = "Custom-CEST-1";
final ZoneOffset standardOffset = ZoneOffset.ofHours(1);
final ZoneOffset summerTimeOffset = ZoneOffset.ofHours(2);
// At least one transistion is required
ZoneOffsetTransition initialTransition = ZoneOffsetTransition.of(
LocalDateTime.of(1601, 1, 1, 3, 0), summerTimeOffset, standardOffset);
List<ZoneOffsetTransition> transitionList = List.of(initialTransition);
// Rules for going to and from summer time (DST)
ZoneOffsetTransitionRule springRule =
ZoneOffsetTransitionRule.of(Month.JANUARY, 1, DayOfWeek.MONDAY, LocalTime.of(2, 0),
false, ZoneOffsetTransitionRule.TimeDefinition.STANDARD, standardOffset,
standardOffset, summerTimeOffset);
ZoneOffsetTransitionRule fallRule =
ZoneOffsetTransitionRule.of(Month.OCTOBER, -1, DayOfWeek.SUNDAY, LocalTime.of(2, 0),
false, ZoneOffsetTransitionRule.TimeDefinition.STANDARD, standardOffset,
summerTimeOffset, standardOffset);
ZoneRules rules = ZoneRules.of(standardOffset, standardOffset,
transitionList, transitionList, List.of(springRule, fallRule));
// The heart of the magic: the ZoneRulesProvider
ZoneRulesProvider customProvider = new ZoneRulesProvider() {
@Override
protected Set<String> provideZoneIds() {
return Set.of(customZoneId);
}
@Override
protected NavigableMap<String, ZoneRules> provideVersions(String zoneId) {
return new TreeMap<>(Map.of(customZoneId, rules));
}
@Override
protected ZoneRules provideRules(String zoneId, boolean forCaching) {
return rules;
}
};
// Registering the ZoneRulesProvider is the key to ZoneId using it
ZoneRulesProvider.registerProvider(customProvider);
// Get an instance of our custom ZoneId
ZoneId customZone = ZoneId.of(customZoneId);
// Transition to standard time was Sunday, October 29, 2017,
// so try the day before and the day after
System.out.println(LocalDate.of(2017, Month.OCTOBER, 28).atStartOfDay(customZone));
System.out.println(LocalDate.of(2017, Month.OCTOBER, 30).atStartOfDay(customZone));
// The special thing about our custom ZoneID is that transition to DST
// happened on Monday, January 1. Try the day before and the day after.
System.out.println(LocalDate.of(2017, Month.DECEMBER, 31).atStartOfDay(customZone));
System.out.println(LocalDate.of(2018, Month.JANUARY, 2).atStartOfDay(customZone));

代码打印：

2017-10-28T00:00+02:00[Custom-CEST-1]
2017-10-30T00:00+01:00[Custom-CEST-1]
2017-12-31T00:00+01:00[Custom-CEST-1]
2018-01-02T00:00+02:00[Custom-CEST-1]

我们看到，在转换到标准时间之前和转换到夏季时间之后，我们得到了预期的夏令时偏移量+02:00。