Date TimeZone conversion

Question

I have done conversion method from UTC String to date in local timezone, but it just returns the same date as in the String. What is wrong here?

 public static Date getUTCToDate(String utc){
    // String exampleOfUTCTime = "2016-09-27T19:35:32.717";

    try{
        Log.d("asd-timeBefore", "getUTCToDate: " + utc);
        DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS");
        formatter.setTimeZone(TimeZone.getDefault());
        Date d = formatter.parse(utc);
        Log.d("asd-timeAfter", "getUTCToDate: " + d);
        return d;
    } catch (ParseException e){
        e.printStackTrace();
    }
    return null;
}

Answer 1

tl;dr

LocalDateTime.parse( "2016-09-27T19:35:32.717" ).atZone( ZoneOffset.UTC )

Details

Your input string is not a UTC value: 2016-09-27T19:35:32.717. That String lacks any information about offset-from-UTC or time zone.

You are using troublesome old date-time classes, now legacy, supplanted by the java.time classes.

LocalDateTime

Parse that string as a LocalDateTime object lacking any offset or time zone.

That input string happens to comply with the ISO 8601 standard for date-time strings. The java.time classes use ISO 8601 formats by default when parsing/generating strings. So no need to specify a formatting pattern.

LocalDateTime ldt = LocalDateTime.parse( "2016-09-27T19:35:32.717" );

OffsetDateTime

If by context you know for certain that string was meant to represent a moment in UTC, then apply an offset to get a OffsetDateTime. Use the predefined constant ZoneOffset.UTC.

OffsetDateTime odt = ldt.atZone( ZoneOffset.UTC );

From there you can use DateTimeFormatter to generate Strings in various formats, if needed.

ZonedDateTime

If you want to view that same moment through the lens of some particular region’s time zone, apply a ZoneId to get a ZonedDateTime.

A time zone is an offset-from-UTC plus a set of rules for handling anomalies such as Daylight Saving Time (DST).

Specify a proper time zone name in the format of continent/region. Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).

ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = odt.atZoneSameInstant( z );

You can get the user’s current default time zone if desired. But be aware this default can change at any moment, even during runtime. So if important, you should ask the user for intended/desired time zone rather than assume.

ZoneId z = ZoneId.systemDefault();

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, .Calendar, & java.text.SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to java.time.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

Where to obtain the java.time classes?

• Java SE 8 and SE 9 and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • See How to use….

The ThreeTen-Extra project 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.

Answer 2

I need to use local timezone since app will be used in various countries.

If you want to format a date on the server side using the client's timezone, then you will have to pass the offset from GMT time in minutes from the client side. Use this JavaScript code:

var offset = new Date().getTimezoneOffset();

then pass this offset to your method as a parameter:

public static Date getUTCToDate(String utc, int offsetInMinutes) {
    // String exampleOfUTCTime = "2016-09-27T19:35:32.717";

    try {
        Log.d("asd-timeBefore", "getUTCToDate: " + utc);
        DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS Z");
        long offset = -1L*60*1000*offsetInMinutes;
        String[] timezones = TimeZone.getAvailableIDs(offset);
        formatter.setTimeZone(timezones[0]);
        Date d = formatter.parse(utc);
        Log.d("asd-timeAfter", "getUTCToDate: " + d);
        return d;
    } catch (ParseException e){
        e.printStackTrace();
    }
    return null;
}

Comments:

You'll notice that I included Z as a date format parameter in your SimpleDateFormat. This will inlcude the time zone displayed as an offset in hours from GMT time.

A Java Date is simply a point in time without regard to an offset. If you want timezone information from the client, you will have to bring it in yourself.

Answer 3

Answers with setTimeZone are correct, but as alternative, you can try to specify UTC in the string itself and indicate that you are using time zone in SimpleDateFormat class, e.g.:

public static Date getUTCToDate(String utc){
    // String exampleOfUTCTime = "2016-09-27T19:35:32.717 UTC";

    try{
        System.out.println("getUTCToDate: " + utc);
        DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS z");
        Date d = formatter.parse(utc);
        System.out.println("getUTCToDate: " + d);
        return d;
    } catch (ParseException e){
        e.printStackTrace();
    }
    return null;
}

Answer 4

If you want to get the formatted date and time in UTC format then you should do like this

formatter.setTimeZone(TimeZone.getTimeZone("UTC"));

Answer 5

Try to change your code, like this. It will convert UTC time zone to local time zone :

public static Date getUTCToDate(String utc){
    // String exampleOfUTCTime = "2016-09-27T19:35:32.717";

    try{
        Log.d("asd-timeBefore", "getUTCToDate: " + utc);
        DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS");
        formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
        Date d = formatter.parse(utc);
        Log.d("asd-timeAfter", "getUTCToDate: " + d);
        return d;
    } catch (ParseException e){
        e.printStackTrace();
    }
    return null;
}