将 Java 日期转换为 OffsetDateTime
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Converting Java Date to OffsetDateTime
提问by user6728767
I have an eta value that is an OffsetDateTime and I have a scheduledDate that is a Date type. If the eta isn't set I want to fall back to the Date.
我有一个 eta 值，它是一个 OffsetDateTime，我有一个 scheduleDate 是一个日期类型。如果 eta 未设置，我想回退到日期。
An example of the date is Tue Jul 21 10:32:28 PDT 2020. To convert this, I tried doing:
OffsetDateTime.ofInstant(dto.getScheduledTime().ToInstant(), ZoneOffset.UTC)
It feels like the utc offset is wrong since the Date has PDT in it already, but at the same time that's also not a timezoneId like "America/Los_Angeles".
日期的一个例子是Tue Jul 21 10:32:28 PDT 2020。为了转换它，我尝试这样做：
OffsetDateTime.ofInstant(dto.getScheduledTime().ToInstant(), ZoneOffset.UTC)
感觉 utc 偏移量是错误的，因为 Date 中已经包含 PDT，但同时它也不是像“America/Los_Angeles”这样的 timezoneId。
I'm a little confused on how to handle this.
我对如何处理这个有点困惑。
采纳答案by Basil Bourque
tl;dr
tl;博士
OffsetDateTime target, eta; // Modern java.time class.
java.util.Date scheduledDate; // Terrible legacy class.
if(Objects.isNull(eta)) { // If no eta, fall back to scheduledDate.
target = scheduledDate.toInstant().atOffset( ZoneOffset.UTC ); // Never use legacy class `java.util.Date` -- when encountered, immediately convert to modern `java.time.Instant`.
} else { // Else not null.
target = eta;
}
return target;
Better to completely avoid java.util.Date. When encountered, immediately convert to modern class Instant, and forget all about the Dateobject.
最好完全避免java.util.Date。遇到时，立即转换为现代类Instant，并忘记所有Date对象。
OffsetDateTime target, eta, scheduled;
scheduled = incomingJavaUtilDate.toInstant().atOffset(ZoneOffset.UTC);
target = Objects.isNull(eta) ? scheduledDate : eta; // Ternary operator. Short way of saying: If eta is null, go with scheduledDate, otherwise go with eta.
return target;
Date::toStringlies to you
Date::toString对你说谎
Firstly, understand that java.util.Daterepresents a moment in UTC, always in UTC?. However, its toStringmethod has the well-intentioned by terribly confusing anti-feature of dynamically applying the JVM's current default time zone. This creates the false impression that Datehas a time zone when in fact it does not?.
首先，了解java.util.Date代表 UTC 的时刻，始终是 UTC吗？. 然而，它的toString方法是善意的，因为动态应用 JVM 的当前默认时区这一非常令人困惑的反特性。这会造成错误的印象，即Date有时区，而实际上没有时区？.
Avoid legacy date-time classes
避免遗留的日期时间类
Secondly, you are needlessly and tragically mixing the very good modern java.timeclasses (OffsetDateTime) with the terribly awful legacy date-time classes (Date). Do not do this. Avoid the legacy classes entirely. They were obsoleted by the adoption of JSR 310back in 2014.
其次，您将非常好的现代java.time类 ( OffsetDateTime) 与非常糟糕的遗留日期时间类 ( Date)混为一谈，这是不必要且可悲的。不要这样做。完全避免遗留类。它们在 2014 年因采用JSR 310而过时。
Use java.time
使用java.time
If handed a java.util.Dateobject, immediately convert to java.time. Call the new conversion methods added to the old classes. The Instantclass directly replaces Date, as a moment in UTC, but with finer resolution of nanoseconds versus milliseconds.
如果交给一个java.util.Date对象，立即转换为java.time。调用添加到旧类的新转换方法。该Instant班可直接替换Date，作为UTC了一下，但纳秒与毫秒更高的分辨率。
Instant instant = myJavaUtilDate.toInstant(); // Convert from legacy class to modern class.
You should generally be tracking moments in UTC. You can do this as an Instantor as a OffsetDateTimewith its offset set to ZoneOffset.UTCconstant.
您通常应该在 UTC 中跟踪时刻。您可以将其作为偏移量设置为常量的anInstant或 aOffsetDateTime来执行ZoneOffset.UTC。
OffsetDateTime odt = instant.atOffset(ZoneOffset.UTC); // Same moment, no change in meaning whatsoever.
For UTC specifically, there is no difference between the instantand the odtin our code here. They both represent a moment in UTC. The difference is that OffsetDateTime(a) could carry an alternate offset-from-UTC value (hours-minutes-seconds), and (b) is more flexible, such as generating text in formats other than standard ISO 8601.
特别是对于 UTC，这里的代码中的instant和之间没有区别odt。它们都代表 UTC 中的一个时刻。不同之处在于OffsetDateTime(a) 可以携带一个替代的 UTC 偏移值（小时-分钟-秒），并且 (b) 更灵活，例如以标准ISO 8601以外的格式生成文本。
Understand that an offset-from-UTCis merely a number of hours, minutes, and seconds. Nothing more. A time zone, in contrast, is muchmore. A time zone is a history of past, present, and future changes to the offset used by the people of a particular region. For example, the people in region using America/Los_Angelestime zone change their offset-from-UTC twice a year in a silly practice known as Daylight Saving Time (DST)going from -08:00 to -07:00 and back again.
了解与 UTC的偏移量仅仅是小时、分钟和秒的数量。而已。一个时区，与此相反，是多了。时区是特定地区人民使用的偏移量的过去、现在和未来变化的历史。例如，使用America/Los_Angeles时区的地区的人们每年两次更改他们与 UTC 的偏移量，这种做法被称为夏令时 (DST)，从 -08:00 到 -07:00 并再次返回。
So generally a time zone is preferable over a mere offset. For example, to see your Datewe turned into a Instantthrough the wall-clock time used by most people on the west coast of US, apply the time zone America/Los_Angeles(ZoneId) to the Instantto get a ZonedDateTime.
所以通常时区比单纯的偏移更可取。例如，看到你Date，我们变成了Instant通过对美国西海岸使用的大多数人的挂钟时间，申请的时区America/Los_Angeles（ZoneId）的Instant获得ZonedDateTime。
ZoneId z = ZoneId.of("America/Los_Angeles");
ZonedDateTime zdt = instant.atZone(z);
You can get back to UTC by extracting a Instant.
您可以通过提取Instant.
Instant instant = zdt.toInstant();
And from there get back to a java.util.Date(if you must, otherwise avoid).
然后从那里回到 a java.util.Date（如果必须，否则避免）。
java.util.Date d = java.util.Date.from(instant);
?Actually, the java.time.Dateclass doeshave a time zone buried deep inside. Lacking any accessor (get/set) methods, it is unreachable. Its behaviors do not relate to our discussion here. Confusing? Yes. Yet another of many reasons to avoid the terrible legacy date-time classes.
? 实际上，java.time.Date班级内部确实有一个时区。缺少任何访问器（get/set）方法，它是无法访问的。它的行为与我们在这里的讨论无关。令人困惑？是的。避免可怕的遗留日期时间类的众多原因中的另一个。
