Getting the current time millis from device and converting it into a new date with different timezone [duplicate]

问题

This question already has answers here:

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How to Parse Date from GMT TimeZone to IST TimeZone and Vice Versa in android (4 answers)

Closed last year.

Here the that problem that i'm facing is -

First i have created a date object which will give me current date and time with device timezone i.e

Date date = new Date(); // Let say the time zone is India - GMT (+05:30)
The value of date is = "Mon Sep 24 13:54:06 GMT+05:30 2018"

No i have a Date formatter using which i have converted the following date object.

SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss z");
sdf.setTimeZone(TimeZone.getTimeZone(loadPreferences(Utility.TIMEZONE_NAME)));
// Here the timezone is Hawaii (GMT-10:00)

Now getting the time as per the new time zone i.e., Hawaii

String dateS = sdf.format(date); 
// This will give you the date with new timezone - "2018/09/23 22:24:06 GMT-10:00"

Now converting this string date to date object as -

Date newDate = sdf.parse(dateS);

Now the new date which i'm getting is not as per the timezone which i have passed.

The value of newDate which i'm getting is = "Mon Sep 24 13:54:06 GMT+05:30 2018" 
//This is device timezone not the one i have set.

I have already tried "Z", "z", "X", "ZZ", "ZZZZZ" in the date formatter still no luck.

If any of you have any idea reading this then let me know.

回答1:

Two messages:

Your expectations are wrong. A Date hasn’t got a time zone, it cannot have. So what you are trying to obtain is impossible using Date and SimpleDateFormat no matter how you write the code.
The classes Date, SimpleDateFormat and TimeZone are long outdated and poorly designed. Their modern replacements are in java.time, the date and time API introduced in 2014.

ZonedDateTime

A modern ZonedDateTime has a time zone as the name says:

    DateTimeFormatter formatter 
            = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss z", Locale.US);
    ZonedDateTime nowInHawaii = ZonedDateTime.now(ZoneId.of("Pacific/Honolulu"));
    String dateS = nowInHawaii.format(formatter);
    System.out.println(dateS);

Output from this snippet was:

2018/09/24 18:43:19 HST

If you want the offset in the output, change the formatter thusly:

    DateTimeFormatter formatter 
            = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss OOOO", Locale.US);

2018/09/24 18:45:53 GMT-10:00

Question: Can I use `java.time` on Android?

Yes, java.time works nicely on older and newer Android devices. It just requires at least Java 6.

In Java 8 and later and on new Android devices (from API level 26, I’m told) the modern API comes built-in.
In Java 6 and 7 get the ThreeTen Backport, the backport of the modern classes (ThreeTen for JSR 310, where the modern API was first described).
On (older) Android, use the Android edition of ThreeTen Backport. It’s called ThreeTenABP. Make sure you import the date and time classes from package org.threeten.bp and subpackages.

Links

Oracle tutorial: Date Time, explaining how to use java.time.
ThreeTen Backport project
ThreeTenABP, Android edition of ThreeTen Backport
Question: How to use ThreeTenABP in Android Project, with a very thorough explanation.
Java Specification Request (JSR) 310.

回答2:

Please try to debug the value that is coming from 'loadPreferences(Utility.TIMEZONE_NAME)' and make sure it is same as "US/Hawaii"

Also try to debug by using this -

sdf.setTimeZone(TimeZone.getTimeZone("US/Hawaii"));

来源：https://stackoverflow.com/questions/52475409/getting-the-current-time-millis-from-device-and-converting-it-into-a-new-date-wi

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java

android

date

time

timezone