英文:
How do I convert a Java Date into an Instant for a given timezone?
问题
我有一个Date类的实例和一个时区（例如Europe/London）。我如何将其转换为Instant？以下是正确的方法吗？
LocalDateTime localDateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
ZonedDateTime zonedDateTime = ZonedDateTime.of(localDateTime, ZoneId.of(timeZone));
Instant instant = zonedDateTime.toInstant();
英文:
I have an instance of the Date class and a time zone (e.g Europe/London). How do I convert this into an Instant? Is the below the correct way of doing this?
LocalDateTime localDateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());
ZonedDateTime zonedDateTime = ZonedDateTime.of(localDateTime, ZoneId.of(timeZone));
Instant instant = zonedDateTime.toInstant();
答案1
得分: 4
# 简而言之
myJavaUtilDate.toInstant()
不需要使用 `LocalDateTime`、`ZoneId`、`ZonedDateTime` 类。
# 详情
你说：
>我有一个 `Date` 类的实例
java.util.Date myJavaUtilDate = … ;
这个类现在已经过时，多年前被 JSR 310 中定义的现代 *java.time* 类所取代。具体而言，被 `java.time.Instant` 取代，用于表示一个时刻，时间轴上的特定点，与 UTC 时区的时间子午线相隔零小时-零分-零秒。
>以及一个时区（例如 Europe/London）
ZoneId z = ZoneId.of( "Europe/London" ) ;
> 如何将其转换为 Instant？
不需要时区。`java.util.Date` 和 `java.time.Instant` 都表示在 UTC 中看到的时刻，如上所述。
对 *旧* 类添加了新的 👉 **转换方法**。查找 `to…` 和 `from…` 的[命名约定][1]。你可以在旧类和现代类之间相互转换。坚持使用现代类。只有在与尚未更新为 *java.time* 的旧代码进行交互时才使用旧的日期时间类。
java.time.Instant instant = myJavaUtilDate.toInstant() ;
另一个方向：
java.util.Date d = java.util.Date.from( instant ) ;
在这个方向上要注意数据丢失。`Instant` 的分辨率为纳秒，而 `java.util.Date` 的分辨率为毫秒。
[1]: https://docs.oracle.com/javase//tutorial/datetime/overview/naming.html
英文:
tl;dr
myJavaUtilDate.toInstant()
No need for LocalDateTime, ZoneId, ZonedDateTime classes.
Details
You said:
>I have an instance of the Date class
java.util.Date myJavaUtilDate = … ;
This class is now legacy, years ago supplanted by the modern java.time classes defined in JSR 310. Specifically replaced by java.time.Instant, to represent a moment, a specific point on the timeline, as seen with an offset of zero hours-minutes-seconds from the temporal meridian of UTC.
>and a time zone (e.g Europe/London)
ZoneId z = ZoneId.of( "Europe/London" ) ;
> How do I convert this into an Instant?
No need for the time zone. Both java.util.Date and java.time.Instant represent a moment as seen in UTC, as described above.
New 👉 conversion methods were added to the old classes. Look for the naming conventions of to… & from…. You can convert back and forth between the legacy classes and the modern classes. Stick to the modern classes. Use the legacy date-time classes only to interoperate with old code not yet updated to java.time.
java.time.Instant instant = myJavaUtilDate.toInstant() ;
And the other direction:
java.util.Date d = java.util.Date.from( instant ) ;
Beware of data loss in this other direction. An Instant has a resolution of nanoseconds, while java.util.Date resolves to milliseconds.
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