在 Java 中将 GMT 转换为 IST？
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Convert GMT to IST in java?
提问by harishtps
I have a GMT field in which the user enter a time to be converted to IST (for eg: in hour field 18, minute field 30, in session field am/pm). I need to get those inputs and convert to IST in java???
我有一个 GMT 字段，用户在其中输入要转换为 IST 的时间（例如：在小时字段 18、分钟字段 30、会话字段 am/pm 中）。我需要获取这些输入并在 java 中转换为 IST ？？？
回答by Michael Borgwardt
This is very easy and obvious if you realize that the timezone is only relevant for a date formatted as String - second/millisecond timestamps (of which java.util.Dateis merely a wrapper) are always implicitly UTC (what GMT is properly called). And converting between such a timestamp and a string always uses a timezone, both ways.
如果您意识到时区仅与格式化为字符串的日期相关，这将非常容易和明显 - 秒/毫秒时间戳（其中java.util.Date只是一个包装器）总是隐含的 UTC（GMT 的正确名称）。并且在这样的时间戳和字符串之间转换总是使用时区，两种方式。
So this is what you need to do:
所以这就是你需要做的：
DateFormat utcFormat = new SimpleDateFormat(patternString);
utcFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
DateFormat indianFormat = new SimpleDateFormat(patternString);
indianFormat .setTimeZone(TimeZone.getTimeZone("Asia/Kolkata"));
Date timestamp = utcFormat.parse(inputString);
String output = indianFormat.format(timestamp);
回答by Erik
Well, joda-time iseasier. Try something like this
那么，乔达时间是比较容易。尝试这样的事情
DateTime dt = new DateTime(<year>,<month>,<day>, <hour>,<minute>, <second>, <millisecond>);
DateTime dtIST = dt.withZone(DateTimeZone.forTimeZone(TimeZone.getTimeZone("IST");
Note here that the use of the three letter abbreviation is deprecated and that time zones should be referred to like "America/Los_Angeles" refers to PST.I haven't the time to get the corrsesponding for IST right now but something should be left as an exercise to the reader!
请注意，这里不推荐使用三个字母的缩写，并且时区应该被称为“America/Los_Angeles”指的是 PST。我现在没有时间获取 IST 的对应信息，但应该保留一些内容给读者的练习！
UPDATE: As Basil Bourque states in the comments, Joda-Time is in maintenance mode. Use java.time instead.
更新：正如 Basil Bourque 在评论中所说，Joda-Time 处于维护模式。改用 java.time。
回答by Basil Bourque
tl;dr
tl;博士
OffsetDateTime.of(
LocalDate.now( ZoneOffset.UTC ) ,
LocalTime.of( 18 , 30 ),
ZoneOffset.UTC
).atZoneSameInstant( ZoneId.of( "Asia/Kolkata" ) )
Details
细节
The modern approach uses the java.time classes.
现代方法使用 java.time 类。
Get the current date in UTCas a LocalDatewithout time-of-day and without time zone or offset.
获取当前日期UTC作为一个LocalDate没有时间的天，没有时区或偏差。
LocalDate localDate = LocalDate.now( ZoneOffset.UTC );
Specify the time per user inputs as a LocalTimewithout a date and without a time zone or offset.
将每个用户输入的时间指定为LocalTime没有日期和时区或偏移量。
LocalTime localTime = LocalTime.of( 18 , 30 );
Put them together with an offset-from-UTCof zero, UTCitself as the constant ZoneOffset.UTC, to get an OffsetDateTime.
将它们与UTC的偏移量为零（UTC本身作为常量 ）放在一起ZoneOffset.UTC，以获得OffsetDateTime.
OffsetDateTime odt = OffsetDateTime.of( localDate , localTime, ZoneOffset.UTC );
Apply a time zone as a ZoneIdto get a ZonedDateTimefor India time. Or by IST did you mean Irish Standard Time? Iran Standard Time?
将时区应用为 aZoneId以获得ZonedDateTime印度时间。或者 IST 是指爱尔兰标准时间吗？伊朗标准时间？
Specify a proper time zone namein the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. Never use the 3-4 letter abbreviation such as ESTor ISTas they are nottrue time zones, not standardized, and not even unique(!).
以、、 或等格式指定正确的时区名称。永远不要使用 3-4 个字母的缩写，例如或因为它们不是真正的时区，不是标准化的，甚至不是唯一的（！）。continent/regionAmerica/MontrealAfrica/CasablancaPacific/AucklandESTIST
ZoneId z = ZoneId.of( "Asia/Kolkata" );
ZonedDateTime zdt = odt.atZoneSameInstant( z );
See this code live at IdeOne.com.
localDate.toString(): 2017-02-13
localTime.toString(): 18:30
odt.toString(): 2017-02-13T18:30Z
zdt.toString(): 2017-02-14T00:00+05:30[Asia/Kolkata]
localDate.toString(): 2017-02-13
localTime.toString(): 18:30
odt.toString(): 2017-02-13T18:30Z
zdt.toString(): 2017-02-14T00:00+05:30[亚洲/加尔各答]
About java.time
关于 java.time
The java.timeframework is built into Java 8 and later. These classes supplant the troublesome old legacydate-time classes such as java.util.Date, Calendar, & SimpleDateFormat.
该java.time框架是建立在Java 8和更高版本。这些类取代了麻烦的旧的遗留日期时间类，例如java.util.Date, Calendar, & SimpleDateFormat。
The Joda-Timeproject, now in maintenance mode, advises migration to the java.timeclasses.
现在处于维护模式的Joda-Time项目建议迁移到java.time类。
To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.
要了解更多信息，请参阅Oracle 教程。并在 Stack Overflow 上搜索许多示例和解释。规范是JSR 310。
Where to obtain the java.time classes?
从哪里获得 java.time 类？
- Java SE 8and SE 9and later
- Built-in.
- Part of the standard Java API with a bundled implementation.
- Java 9 adds some minor features and fixes.
- Java SE 6and SE 7
- Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
- Android
- The ThreeTenABPproject adapts ThreeTen-Backport(mentioned above) for Android specifically.
- See How to use ThreeTenABP….
- Java SE 8和SE 9及更高版本
- 内置。
- 具有捆绑实现的标准 Java API 的一部分。
- Java 9 添加了一些小功能和修复。
- Java SE 6和SE 7
- 多的java.time功能后移植到Java 6和7在ThreeTen-反向移植。
- 安卓
- 所述ThreeTenABP项目适应ThreeTen-反向移植（上述）为Android特异性。
- 请参阅如何使用ThreeTenABP ...。
The ThreeTen-Extraproject extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.
该ThreeTen-额外项目与其他类扩展java.time。该项目是未来可能添加到 java.time 的试验场。你可能在这里找到一些有用的类，比如Interval，YearWeek，YearQuarter，和更多。
回答by felix Antony
When I add the below code, it worked for me.
当我添加以下代码时，它对我有用。
DateFormat utcFormat = new SimpleDateFormat("yyyy-MM-dd-HH-mm");
utcFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
DateFormat indianFormat = new SimpleDateFormat("dd-HH-mm");
utcFormat.setTimeZone(TimeZone.getTimeZone("IST"));
Date timestamp = utcFormat.parse("2019-04-26-19-00");
String istTime = indianFormat.format(timestamp);
