Timezone conversion
I need to convert from one timezone to another timezone in my project.
I am able to convert from my current timezone to another but not from a different timezone to another.
For example I am in India, and I am able to convert from India to US using Date d=new Date(); and assigning it to a calendar object and setting the time zone.
However, I cannot do this from different timezone to another timezone. For example, I am in India, but I am having trouble converting timezones from the US to the UK.
Solution 1:
tl;dr
ZonedDateTime.now( ZoneId.of( "Pacific/Auckland" )) // Current moment in a particular time zone.
.withZoneSameInstant( ZoneId.of( "Asia/Kolkata" )) // Same moment adjusted into another time zone.
Details
The java.util.Date class has no time zone assigned†, yet it's toString implementation confusingly applies the JVM's current default time zone.
Avoid java.util.Date & .Calendar
This is one of many reasons to avoid the notoriously troublesome java.util.Date, .Calendar, and SimpleDateFormat classes bundled with Java. Avoid them. Instead use either:
- The java.time package built into Java 8 and inspired by Joda-Time.
- Joda-Time
java.time
Java 8 and later has the java.time package built-in. This package was inspired by Joda-Time. While they share some similarities and class names, they are different; each has features the other lacks. One notable difference is that java.time avoids constructors, instead uses static instantiation methods. Both frameworks are led by the same man, Stephen Colbourne.
Much of the java.time functionality has been back-ported to Java 6 & 7 in the ThreeTen-Backport project. Further adapted to Android in the ThreeTenABP project.
In the case of this Question, they work in the same fashion. Specify a time zone, and call a now method to get current moment, then create a new instance based on the old immutable instance to adjust for time zone.
Note the two different time zone classes. One is a named time zone including all the rules for Daylight Saving Time and other such anomalies plus an offset from UTC while the other is only the offset.
ZoneId zoneMontréal = ZoneId.of("America/Montreal");
ZonedDateTime nowMontréal = ZonedDateTime.now ( zoneMontréal );
ZoneId zoneTokyo = ZoneId.of("Asia/Tokyo");
ZonedDateTime nowTokyo = nowMontréal.withZoneSameInstant( zoneTokyo );
ZonedDateTime nowUtc = nowMontréal.withZoneSameInstant( ZoneOffset.UTC );
Joda-Time
Some example code in Joda-Time 2.3 follows. Search StackOveflow for many more examples and much discussion.
DateTimeZone timeZoneLondon = DateTimeZone.forID( "Europe/London" );
DateTimeZone timeZoneKolkata = DateTimeZone.forID( "Asia/Kolkata" );
DateTimeZone timeZoneNewYork = DateTimeZone.forID( "America/New_York" );
DateTime nowLondon = DateTime.now( timeZoneLondon ); // Assign a time zone rather than rely on implicit default time zone.
DateTime nowKolkata = nowLondon.withZone( timeZoneKolkata );
DateTime nowNewYork = nowLondon.withZone( timeZoneNewYork );
DateTime nowUtc = nowLondon.withZone( DateTimeZone.UTC ); // Built-in constant for UTC.
We have four representations of the same moment in the timeline of the Universe.
†Actually the java.util.Date class does have a time zone buried within its source code. But the class ignores that time zone for most practical purposes. So, as shorthand, it’s often said that j.u.Date has no time zone assigned. Confusing? Yes. Avoid the mess that is j.u.Date and go with Joda-Time and/or java.time.
Solution 2:
Some examples
Convert time between timezone
Converting Times Between Time Zones
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.TimeZone;
public class TimeZoneExample {
public static void main(String[] args) {
// Create a calendar object and set it time based on the local
// time zone
Calendar localTime = Calendar.getInstance();
localTime.set(Calendar.HOUR, 17);
localTime.set(Calendar.MINUTE, 15);
localTime.set(Calendar.SECOND, 20);
int hour = localTime.get(Calendar.HOUR);
int minute = localTime.get(Calendar.MINUTE);
int second = localTime.get(Calendar.SECOND);
// Print the local time
System.out.printf("Local time : %02d:%02d:%02d\n", hour, minute, second);
// Create a calendar object for representing a Germany time zone. Then we
// wet the time of the calendar with the value of the local time
Calendar germanyTime = new GregorianCalendar(TimeZone.getTimeZone("Europe/Berlin"));
germanyTime.setTimeInMillis(localTime.getTimeInMillis());
hour = germanyTime.get(Calendar.HOUR);
minute = germanyTime.get(Calendar.MINUTE);
second = germanyTime.get(Calendar.SECOND);
// Print the local time in Germany time zone
System.out.printf("Germany time: %02d:%02d:%02d\n", hour, minute, second);
}
}
Solution 3:
Date date = new Date();
String formatPattern = ....;
SimpleDateFormat sdf = new SimpleDateFormat(formatPattern);
TimeZone T1;
TimeZone T2;
// set the Calendar of sdf to timezone T1
sdf.setTimeZone(T1);
System.out.println(sdf.format(date));
// set the Calendar of sdf to timezone T2
sdf.setTimeZone(T2);
System.out.println(sdf.format(date));
// Use the 'calOfT2' instance-methods to get specific info
// about the time-of-day for date 'date' in timezone T2.
Calendar calOfT2 = sdf.getCalendar();
Solution 4:
The "default" time zone can be avoided entirely by just setting the time zone appropriately for the Calendar object. However, I would personally suggest that you use Joda Time as a far superior API for date and time operations in Java. Amongst other things, time zone conversion is very simple in Joda.
It's not clear what your current code looks like and why you're only able to convert via the default time zone, but in Joda Time you'd just specify the time zone explicitly when creating (say) a DateTime object, and then use withZone(DateTimeZone zone).
If you could tell us more about how you're getting input data, we could give a fuller example.