Overriding a Java application’s time zone

Your application’s time zone is usually determined by the machine’s time zone on which the app is running. Sometimes, however, you may need to override the time zone the application thinks it’s in.

To change the time zone for a particular application without changing the machine’s time zone, set the system property user.timezone to the time zone that you want your program to run in. You can set this system property when you start the virtual machine by passing a command line parameter:

java -Duser.timezone=UTC TimeZoneTip

The class below creates a Date object and prints it to standard out:

public class TimeZoneTip {
public static void main(String args[]) {
System.out.println(new java.util.Date());
}
}

When the program is run without the user.timezone property set, the output is:

Sun Jun 28 19:38:27 EDT 2003

In this case, the time zone defaulted to the time zone of the machine the program was running on: Eastern Daylight Time (EDT).

When the program is run with the user.timezone property set to Coordinated Universal Time (UTC), the output is:

Sun Jun 28 23:39:59 UTC 2003

When you need an application to run in a particular time zone, the solution is just a switch away. There are other system properties that can affect your application’s environment. Check out the tool documentation for the Java virtual machine to find out more.