How to use DateTimeZone in Java

Question

I've been trying to convert a server's date and time to user's one with the following code

@Test
public void playingWithJodaTime() {

    LocalDateTime localDateTime = new LocalDateTime();
    System.out.println("server localDateTime : "
            + localDateTime.toDateTime(DateTimeZone.getDefault()).toDate());
    System.out.println("user's localDateTime : "
            + localDateTime.toDateTime(DateTimeZone.forID("Asia/Jakarta"))
                    .toDate());
}

Printed result

server localDateTime : Tue Dec 17 00:04:29 SGT 2013
user's localDateTime : Tue Dec 17 01:04:29 SGT 2013

However the printed result is not like what I expected since the server time zone is (UTC+08:00) Kuala Lumpur, Singapore while the user's is (UTC+07:00) Bangkok, Hanoi, Jakarta.

What did I do wrong here ?

Answer 1

You are converting DateTime to java Date (why?).
java.util.Date uses default JVM's time zone
So, you missed time zone at this conversion.

This example works as expected:

LocalDateTime localDateTime = new LocalDateTime();
System.out.println("server localDateTime : "
        + localDateTime.toDateTime(DateTimeZone.getDefault()));
System.out.println("user's localDateTime : "
        + localDateTime.toDateTime(DateTimeZone.forID("Asia/Jakarta")));  

if you want to convert joda DateTime to something else, then convert it to Calendar

  LocalDateTime localDateTime = new LocalDateTime();
  System.out.println("server localDateTime : "
        + localDateTime.toDateTime(DateTimeZone.getDefault()).toGregorianCalendar());
  System.out.println("user's localDateTime : "
        + localDateTime.toDateTime(DateTimeZone.forID("Asia/Jakarta")).toGregorianCalendar());

Answer 2

The error is the use of toDate(). Why? By saying toDate() you convert your LocalDateTime to a java.util.Date which is timezone-independent. But then you use implicitly the toString()-method on j.u.Date which uses your default timezone, so in both cases you get the same representation.

The solution is just to leave out the call of toDate(). JodaTime objects have better toString()-implementations closely following ISO standard and will print the result in different timezones as you have specified.