Java, How to change GMT time to local time?

Question

Server sends me time like this:

2012-06-08 17:00:00 +0100

I need to change it like HH:MM based on local time. For example this time is what time at Japan, India, US and etc.

How can I do this? Thanks

Answer 1

Option 1: using java.util.Date/Calendar:

First you need to parse the value to a Date, then reformat it in the format and time zone you're interested in:

SimpleDateFormat inputFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss z",
                                                    Locale.US);
Date date = inputFormat.parse(inputText);

// Potentially use the default locale. This will use the local time zone already.
SimpleDateFormat outputFormat = new SimpleDateFormat("HH:mm", Locale.US);
String outputText = outputFormat.format(date);

Option 2: using Joda Time

Joda Time is a much better date/time library for Java.

DateTimeFormatter inputFormatter = DateTimeFormat
    .forPattern("yyyy-MM-dd HH:mm:ss Z")
    .withLocale(Locale.US);

DateTime parsed = inputFormatter.parseDateTime(inputText);

DateTimeFormatter outputFormatter = DateTimeFormat
    .forPattern("HH:mm")
    .withLocale(Locale.US)
    .withZone(DateTimeZone.getDefault());

String outputText = outputFormatter.print(parsed);

Note that you should only convert to/from string representations when you really need to. Otherwise, use the most appropriate type based on your usage - this is where Joda Time really shines.

Answer 2

Use JodaTime. It's far better and safer than Java's Date and Time API. There are a lot of methods that return a LocalTime object (HH:MM).

As an example, new DateTime(your date time).toLocalTime();

Answer 3

java.util.Date is always in UTC. What makes you think it's in local time? I suspect the problem is that you're displaying it via an instance of Calendar which uses the local timezone, or possibly using Date.toString() which also uses the local timezone.

If this isn't the problem, please post some sample code.

I would, however, recommend that you use Joda Time anyway, which offers a much clearer API.

Answer 4

The other Answers are correct but outdated. Use java.time classes instead.

tl;dr

ZonedDateTime zdt_Kolkata = OffsetDateTime.parse( "2012-06-08 17:00:00 +0100" , DateTimeFormatter.ofPattern( "yyyy-MM-dd HH:mm:ss Z" ) ).atZone( ZoneId.of( "Asia/Kolkata" ) );

Using java.time

Define a DateTimeFormatter formatting pattern to match your input String.

String input = "2012-06-08 17:00:00 +0100";
DateTimeFormatter f = DateTimeFormatter.ofPattern( "yyyy-MM-dd HH:mm:ss Z" );

OffsetDateTime

Parse the String as an OffsetDateTime object that represents the +0100 in your input which means “one hour ahead of UTC”.

OffsetDateTime odt = OffsetDateTime.parse( input , f ); 

ZonedDateTime

Apply a ZoneId to produce a ZonedDateTime for any desired time zone. Specify a proper time zone name. 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 zoneId_Kolkata = ZoneId.of( "Asia/Kolkata" ); // India
ZonedDateTime zdt_Kolkata = odt.atZone( zoneId_Kolkata );

…and another…

ZoneId zoneId_Montréal = ZoneId.of( "Asia/Montreal" ); // Québec Canada
ZonedDateTime zdt_Montréal = odt.atZone( zoneId_Montréal );

Instant

For UTC, extract an Instant object. The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds.

Instant instant = zdt_Montréal.toInstant();

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the old troublesome 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.

Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport and further adapted to Android in ThreeTenABP.

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time.