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javadatetime
Viswanath Alikonda
Viswanath Alikonda

Reputation: 137

Calendar in Java is not working for UTC timezone

My code:

TimeZone timeZone = TimeZone.getTimeZone("UTC");
Calendar cal = (Calendar) Calendar.getInstance(timeZone);
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EE MMM dd HH:mm:ss zzz yyyy", Locale.US);
System.out.println("Gregorian cal time:"+cal.getTime());
System.out.println("utc time: "+simpleDateFormat.format(cal.getTime()));

Both the print statements are showing the same local time.

Upvotes: 0

Views: 628

Answers (3)

Basil Bourque
Basil Bourque

Reputation: 338574

tl;dr

Instant.now()

Avoid legacy date-time classes

You are using troublesome old date-time classes, now legacy, supplanted by the java.time classes. The legacy classes are an awful mess, poorly designed, confusing, and flawed. Avoid them.

Instant

The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction). 

Instant instant = Instant.now();

instant.toString(): 2017-02-23T03:30:58.431Z

The format of that string generated by toString is standard ISO 8601 format. The Z on the end is short for Zulu and means UTC.

That's it, you are done.

ZonedDateTime

If you want to see that same moment as the wall-clock time of some particular region, then apply a ZoneId to get a ZonedDateTime.

Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland. 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( "Asia/Kolkata" );
ZonedDateTime zdt = instant.atZone( z );

zdt.toString(): 2017-02-23T09:00:58.431+05:30[Asia/Kolkata]

India is five and a half hours ahead of UTC. So when adjusted into Asia/Kolkata time zone, note how the time-of-day jumps from 03:30 to 09:00.

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, & SimpleDateFormat.

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

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?

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, andfz more.

Upvotes: 0

Thomas Fritsch
Thomas Fritsch

Reputation: 10127

You need to set the TimeZone of your DateFormatter to "UTC"

SimpleDateFormat simpleDateFormat = new SimpleDateFormat("EE MMM dd HH:mm:ss zzz yyyy", Locale.US);
simpleDateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
System.out.println("utc time: "+simpleDateFormat.format(cal.getTime()));

Upvotes: 1

Viswanath Alikonda
Viswanath Alikonda

Reputation: 137

LocalDateTime utc_time = LocalDateTime.now(ZoneId.of("UTC"));
System.out.println("Date: "+utc_time);

works fine

Upvotes: 0

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