Question

我使用Java 8的新java.time实现，并想知道UTC到CET时间转换结果的输出。

ZonedDateTime utcTime = ZonedDateTime.of(2014, 7, 1, 8, 0, 0, 0, ZoneId.of("UTC"));
ZonedDateTime cetTime = ZonedDateTime.ofInstant(utcTime.toInstant(), ZoneId.of("CET"));
System.out.println("Summer-UTC-Time: " + utcTime);
System.out.println("Summer-CET-Time: " + cetTime);

System.out.println();

utcTime = ZonedDateTime.of(2014, 1, 1, 8, 0, 0, 0, ZoneId.of("UTC"));
cetTime = ZonedDateTime.ofInstant(utcTime.toInstant(), ZoneId.of("CET"));
System.out.println("Winter-UTC-Time: " + utcTime);
System.out.println("Winter-CET-Time: " + cetTime);

我预计CET时间总是+1时间，但我得到了：

Summer-UTC-Time: 2014-07-01T08:00Z[UTC]
Summer-CET-Time: 2014-07-01T10:00+02:00[CET] -> +2 **Unexpected**

Winter-UTC-Time: 2014-01-01T08:00Z[UTC]
Winter-CET-Time: 2014-01-01T09:00+01:00[CET] -> +1 Expected

显然我必须处理夏令时，这是我在使用CET时没想到的。 java.time CET真的是CEST吗？如果是，如果我需要CET，我应该使用哪个区域？

Answer 1

IANA definition of CET符合中欧的时区规则，包括冬季和夏季时间。可以看到规则here，其中显示“CET”基于"C-Eur"，其中包括夏令时。

在java.time中，您还可以看到完整的规则集：

ZoneId zone = ZoneId.of("CET");
System.out.println(zone);
System.out.println(zone.getRules());
for (ZoneOffsetTransition trans : zone.getRules().getTransitions()) {
  System.out.println(trans);
}
for (ZoneOffsetTransitionRule rule : zone.getRules().getTransitionRules()) {
  System.out.println(rule);
}

打印：

CET
ZoneRules[currentStandardOffset=+01:00]
Transition[Gap at 1916-04-30T23:00+01:00 to +02:00]
Transition[Overlap at 1916-10-01T01:00+02:00 to +01:00]
Transition[Gap at 1917-04-16T02:00+01:00 to +02:00]
Transition[Overlap at 1917-09-17T03:00+02:00 to +01:00]
Transition[Gap at 1918-04-15T02:00+01:00 to +02:00]
Transition[Overlap at 1918-09-16T03:00+02:00 to +01:00]
Transition[Gap at 1940-04-01T02:00+01:00 to +02:00]
Transition[Overlap at 1942-11-02T03:00+02:00 to +01:00]
Transition[Gap at 1943-03-29T02:00+01:00 to +02:00]
Transition[Overlap at 1943-10-04T03:00+02:00 to +01:00]
Transition[Gap at 1944-04-03T02:00+01:00 to +02:00]
Transition[Overlap at 1944-10-02T03:00+02:00 to +01:00]
Transition[Gap at 1945-04-02T02:00+01:00 to +02:00]
Transition[Overlap at 1945-09-16T03:00+02:00 to +01:00]
Transition[Gap at 1977-04-03T02:00+01:00 to +02:00]
Transition[Overlap at 1977-09-25T03:00+02:00 to +01:00]
Transition[Gap at 1978-04-02T02:00+01:00 to +02:00]
Transition[Overlap at 1978-10-01T03:00+02:00 to +01:00]
Transition[Gap at 1979-04-01T02:00+01:00 to +02:00]
Transition[Overlap at 1979-09-30T03:00+02:00 to +01:00]
Transition[Gap at 1980-04-06T02:00+01:00 to +02:00]
Transition[Overlap at 1980-09-28T03:00+02:00 to +01:00]
Transition[Gap at 1981-03-29T02:00+01:00 to +02:00]
Transition[Overlap at 1981-09-27T03:00+02:00 to +01:00]
Transition[Gap at 1982-03-28T02:00+01:00 to +02:00]
Transition[Overlap at 1982-09-26T03:00+02:00 to +01:00]
Transition[Gap at 1983-03-27T02:00+01:00 to +02:00]
Transition[Overlap at 1983-09-25T03:00+02:00 to +01:00]
Transition[Gap at 1984-03-25T02:00+01:00 to +02:00]
Transition[Overlap at 1984-09-30T03:00+02:00 to +01:00]
Transition[Gap at 1985-03-31T02:00+01:00 to +02:00]
Transition[Overlap at 1985-09-29T03:00+02:00 to +01:00]
Transition[Gap at 1986-03-30T02:00+01:00 to +02:00]
Transition[Overlap at 1986-09-28T03:00+02:00 to +01:00]
Transition[Gap at 1987-03-29T02:00+01:00 to +02:00]
Transition[Overlap at 1987-09-27T03:00+02:00 to +01:00]
Transition[Gap at 1988-03-27T02:00+01:00 to +02:00]
Transition[Overlap at 1988-09-25T03:00+02:00 to +01:00]
Transition[Gap at 1989-03-26T02:00+01:00 to +02:00]
Transition[Overlap at 1989-09-24T03:00+02:00 to +01:00]
Transition[Gap at 1990-03-25T02:00+01:00 to +02:00]
Transition[Overlap at 1990-09-30T03:00+02:00 to +01:00]
Transition[Gap at 1991-03-31T02:00+01:00 to +02:00]
Transition[Overlap at 1991-09-29T03:00+02:00 to +01:00]
Transition[Gap at 1992-03-29T02:00+01:00 to +02:00]
Transition[Overlap at 1992-09-27T03:00+02:00 to +01:00]
Transition[Gap at 1993-03-28T02:00+01:00 to +02:00]
Transition[Overlap at 1993-09-26T03:00+02:00 to +01:00]
Transition[Gap at 1994-03-27T02:00+01:00 to +02:00]
Transition[Overlap at 1994-09-25T03:00+02:00 to +01:00]
Transition[Gap at 1995-03-26T02:00+01:00 to +02:00]
Transition[Overlap at 1995-09-24T03:00+02:00 to +01:00]
Transition[Gap at 1996-03-31T02:00+01:00 to +02:00]
Transition[Overlap at 1996-10-27T03:00+02:00 to +01:00]
Transition[Gap at 1997-03-30T02:00+01:00 to +02:00]
Transition[Overlap at 1997-10-26T03:00+02:00 to +01:00]
TransitionRule[Gap +01:00 to +02:00, SUNDAY on or after MARCH 25 at 02:00 STANDARD, standard offset +01:00]
TransitionRule[Overlap +02:00 to +01:00, SUNDAY on or after OCTOBER 25 at 02:00 STANDARD, standard offset +01:00]

这里的关键是要了解时区标识符和该标识符的"short name"是两个不同的元素。标识符始终固定为“CET”，但名称在“CET”和“CEST”之间更改。

Answer 2

因为您知道偏移并且不想使用DTS，为什么不使用ZoneOffset.ofHours(1)方法而不是ZoneId.of("CET")？

~~此外，你可以在任何ZoneId实例上调用normalized()使其成为一个固定的偏移，但听起来不如从开头使用偏移量那么可靠。~~

来自ZoneId javadoc：

ZoneId用于标识用于在a之间进行转换的规则   即时和LocalDateTime。有两种不同类型的ID：


固定偏移 - 与UTC / Greenwich完全解析的偏移量，对所有本地日期时间使用相同的偏移量

地理区域 - 用于查找从UTC /格林威治的偏移量的特定规则集适用的区域


大多数固定偏移量由ZoneOffset表示。调用normalized（）   在任何ZoneId上将确保将表示固定的偏移ID   作为ZoneOffset。

如果您没有使用固定偏移量，那么您正在使用地理区域，这意味着如果观察到DTS，它将取决于该区域。 PST也是如此。即使夏季时间被称为PDT，你也会看到它观察DTS。是的，这令人困惑，但这是大多数工具的工作方式。请阅读完整的ZoneId javadoc以获得更详尽的说明（Time-zone IDs部分）。

java.time：CET时区是否考虑夏令时？

2 个答案: