Java 如何使日期与语言环境无关？
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How to make Date locale-independent?
提问by folone
I have a db, that stores dates in OleDateTimeformat, in GMT timezone. I've implemented a class, extending Datein java to represent that in classic date format. But my class is locale-dependent (I'm in GMT+2). Therefore, it converts the date in the db as date - 2 hours. How do I make it convert the date correctly? I want my class to be locale-independent, always using GMT timezone. Actually, the question is:
我有一个数据库，它OleDateTime以格林威治标准时间时区的格式存储日期。我已经实现了一个类，Date在 java 中扩展以表示经典日期格式。但是我的课程是语言环境相关的（我在 GMT+2）。因此，它将数据库中的日期转换为date - 2 hours. 如何让它正确转换日期？我希望我的课程与语言环境无关，始终使用 GMT 时区。其实问题是：
class MyOleDateTime extends Date {
static {
Locale.setDefault(WhatGoesHere?)
}
// ... some constructors
// ... some methods
}
采纳答案by Alexander Temerev
Well, it's better to use the Calendar object like suggested in other answers. However, if you reallywant to set global timezone, you can use TimeZone.setDefault(TimeZone.getTimeZone("UTC"));early in your application code. There is also user.timezoneJava system property.
好吧，最好像其他答案中建议的那样使用 Calendar 对象。但是，如果您确实想设置全局时区，则可以TimeZone.setDefault(TimeZone.getTimeZone("UTC"));在应用程序代码的早期使用。还有user.timezoneJava系统属性。
Also (just fun to know), it appears that the only country actually living by GMT/UTC time (without daylight saving changes) is Liberia.
另外（知道很有趣），似乎唯一实际生活在 GMT/UTC 时间（没有夏令时更改）的国家是利比里亚。
In fact, Dateobjects per se are alwayslocale- and timezone-independent. Its getTime()method will always return the number of milliseconds passed since January 1, 1970 00:00:00 (not counting leap seconds) in UTC. But if you want to get something else than milliseconds, you have to use Calendar, which istimezone-dependent. But it is the right way to go. You don't use that deprecated methods in Dateclass, do you?
事实上，Date对象本身总是与语言环境和时区无关的。它的getTime()方法将始终以 UTC 形式返回自 1970 年 1 月 1 日 00:00:00（不计算闰秒）以来经过的毫秒数。但是，如果你想要得到的东西比别的毫秒，你必须使用Calendar，这是时区相关。但这是正确的方法。你不会在Date课堂上使用那些不推荐使用的方法，对吗？
回答by kgiannakakis
回答by Michael Borgwardt
A Dateislocale-independent, always using GMT timezone. It's just a wrapper around a millisecond timestamp in GMT (more correctly: UTC).
一个日期是语言环境无关，总是使用GMT时区。它只是 GMT 中毫秒时间戳的包装器（更准确地说：UTC）。
The only things in Datethat are timezone dependant are the deprecated methods like getDay()- that's why they're deprecated. Those use the default time zone. The correct thing to do is to avoid using those deprecated methods - notto set the default timezone to UTC! That could cause problems elsewhere, and you can't prevent other parts of the code from setting the default timezone to something else.
唯一Date与时区相关的是不推荐使用的方法，例如getDay()- 这就是不推荐使用它们的原因。那些使用默认时区。正确的做法是避免使用那些已弃用的方法 -不要将默认时区设置为 UTC！这可能会导致其他地方出现问题，并且您无法阻止代码的其他部分将默认时区设置为其他内容。
回答by Jesper
As Michael Borgwardt has already said, the Java Dateobject does not know anything about timezones. It's just a wrapper for a number of milliseconds since 01-01-1970 00:00:00 UTC.
正如 Michael Borgwardt 已经说过的，JavaDate对象对时区一无所知。它只是自 01-01-1970 00:00:00 UTC 以来数毫秒的包装器。
You start dealing with timezones only when you for example convert the Dateobject to a Stringusing a DateFormat. You set the timezone on the DateFormatto specify in which timezone you want to see the Date.
例如，只有当您使用 a将Date对象转换为 a时，您才开始处理时区。您在 上设置时区以指定要在哪个时区中查看.StringDateFormatDateFormatDate
DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss Z");
df.setTimeZone(TimeZone.getTimeZone("UTC"));
String text = df.format(date); // text will contain date represented in UTC
回答by James Ovcarik
Here's a snippet I used to calculate the GMT offset from the Calendarinstance and format it. I appreciate all the help I've gotten from this site, its nice to contribute. I hope this helps someone somewhere. Enjoy.
这是我用来计算Calendar实例的 GMT 偏移量并对其进行格式化的片段。我感谢我从这个网站得到的所有帮助，很高兴做出贡献。我希望这可以帮助某个地方的人。享受。
Calendar calInst = Calendar.getInstance();
//calculate the offset to keep calendar instance GMT
int gmtOffsetMilli = calInst.get(Calendar.ZONE_OFFSET);
long gmtOffsetHr = TimeUnit.HOURS.convert(gmtOffsetMilli, TimeUnit.MILLISECONDS);
calInst = Calendar.getInstance(TimeZone.getTimeZone("GMT " + gmtOffsetHr));
