在 Java 8 中获取当前时间
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Getting current time in Java 8
提问by user2693135
I am exploring the new java.time API of Java 8. I am particularly trying to retrieve the current time (my current time zone, of a different time zone, and of a different offset).
我正在探索 Java 8 的新 java.time API。我特别想检索当前时间（我的当前时区、不同时区和不同偏移量）。
The code is:
代码是：
public static void getCurrentLocalTime(){
LocalTime time = LocalTime.now();
System.out.println("Local Time Zone: "+ZoneId.systemDefault().toString());
System.out.println("Current local time : " + time);
}
public static void getCurrentTimeWithTimeZone(){
LocalDateTime localtDateAndTime = LocalDateTime.now();
ZoneId zoneId = ZoneId.of("America/Los_Angeles");
ZonedDateTime dateAndTimeInLA = ZonedDateTime.of(localtDateAndTime, zoneId);
String currentTimewithTimeZone =dateAndTimeInLA.getHour()+":"+dateAndTimeInLA.getMinute();
System.out.println("Current time in Los Angeles: " + currentTimewithTimeZone);
}
public static void getCurrentTimeWithZoneOffset(){
LocalTime localtTime = LocalTime.now();
ZoneOffset offset = ZoneOffset.of("-08:00");
OffsetTime offsetTime = OffsetTime.of(localtTime, offset);
String currentTimewithZoneOffset =offsetTime.getHour()+":"+offsetTime.getMinute();
System.out.println("Current time with offset -08:00: " + currentTimewithZoneOffset);
}
But, when I call the methods I get the same time-of-day (my system time), which is obviously not what I am expecting.
但是，当我调用这些方法时，我得到了相同的时间（我的系统时间），这显然不是我所期望的。
The output of the method calls:
方法调用的输出：
Current time in Los Angeles: 19:59
Local Time Zone: Asia/Calcutta
Current local time : 19:59:20.477
Current time with offset -08:00: 19:59
Even after setting a different time zone and offset, why am I getting the same time?
即使设置了不同的时区和偏移量，为什么我得到相同的时间？
回答by assylias
LocalDateTime.now()always returns the current date/time in your default timezone (say 13 October @ 11.20am in London). When you create a ZonedDateTimeor OffsetTimefrom it with a specific ZoneIdor ZoneOffset, you get the same date and time but in a different time zone (for example 13 october at 11.20am in Los Angeles), which represents a different instant in time.
LocalDateTime.now()始终返回默认时区中的当前日期/时间（比如伦敦的 10 月 13 日 @ 11.20am）。当您使用特定的or创建 a ZonedDateTimeor 时，您将获得相同的日期和时间，但位于不同的时区（例如，洛杉矶的 10 月 13 日上午 11 点 20 分），这代表了不同的时刻。OffsetTimeZoneIdZoneOffset
You are probably looking for something like:
您可能正在寻找类似的东西：
Instant now = Instant.now();
ZoneId zoneId = ZoneId.of("America/Los_Angeles");
ZonedDateTime dateAndTimeInLA = ZonedDateTime.ofInstant(now, zoneId);
This will calculate the current date and time in Los Angeles: 13 october, 3.20am.
这将计算洛杉矶的当前日期和时间：10 月 13 日，凌晨 3 点。
回答by Tunaki
Consider the following fixed methods:
考虑以下固定方法：
public static void getCurrentLocalTime() {
LocalTime time = LocalTime.now();
System.out.println("Local Time Zone: " + ZoneId.systemDefault().toString());
System.out.println("Current local time : " + time);
}
public static void getCurrentTimeWithTimeZone() {
LocalDateTime localDateAndTime = LocalDateTime.now(ZoneId.of("America/Los_Angeles"));
System.out.println("Current time in Los Angeles: " + localDateAndTime.toLocalTime());
}
public static void getCurrentTimeWithZoneOffset() {
LocalTime localTime = LocalTime.now(ZoneOffset.of("-08:00"));
System.out.println("Current time with offset -08:00: " + localTime);
}
What changed is that instead of calling now(), the call is made to now(zone). That is because now()always return the current system time in your time-zone. The calls to atZone, OffsetTime.ofor ZoneDateTime.ofdo not change the date/time, it only tells Java Time that the date should be understood at a date/time in this timezone.
改变的是，不是调用now()，而是调用now(zone). 那是因为now()始终以您的时区返回当前系统时间。到通话atZone，OffsetTime.of或ZoneDateTime.of不更改日期/时间，它只是告诉Java的时间日期应该在这个时区的日期/时间来理解。
When calling these 3 methods, here's the output on my machine:
调用这 3 个方法时，这是我机器上的输出：
Local Time Zone: Europe/Paris
Current local time : 12:32:21.560
Current time in Los Angeles: 03:32:21.579
Current time with offset -08:00: 02:32:21.580
To make this very clear: you're in Europe and call LocalDateTime.now().atZone(ZoneId.of("America/Los_Angeles"))- you are creating a date/time which represents the current-time in Europe as if you were located in Los Angeles, so you are creating a date/time which is actually in the futurefor Los Angeles residents (8 or 9 hours in the future, depending on DST).
明确地说：您在欧洲并打电话LocalDateTime.now().atZone(ZoneId.of("America/Los_Angeles"))- 您正在创建一个日期/时间来表示欧洲的当前时间，就好像您位于洛杉矶一样，因此您正在创建一个实际上在的日期/时间洛杉矶居民的未来（未来8 或 9 小时，取决于夏令时）。
回答by mlewandowski
There is also another way of displaying time in another zone by using withZoneSameInstant:
还有另一种显示另一个区域的时间的方法withZoneSameInstant：
// now, in current zone,
// 2016-04-13T14:24:57.618+02:00[Europe/Warsaw]
ZonedDateTime now = ZonedDateTime.now();
// 2016-04-13T05:24:57.618-07:00[America/Los_Angeles]
ZonedDateTime losAngelesDateTime = now.withZoneSameInstant(ZoneId.of("America/Los_Angeles"));
