Java Default Timezone Issue Under Linux

1、Description
I encountered a problem with Java 1.7 running under Redhat Linux where Java was not detecting the correct default timezone from the operating system. It was defaulting to the

US/Pacific

timezone even though the Linux date command returned the correct timezone (

US/Eastern

in my case).To test what the default timezone of your JVM is, compile and run the following code:

import java.util.Date;
import java.util.TimeZone;

public class TimeTest {

public static void main(String args[]) {
long time = System.currentTimeMillis();
String millis = Long.toString(time);
Date date = new Date(time);
System.out.println("Current time in milliseconds = " + millis + " => " + date.toString());
System.out.println("Current time zone: " + TimeZone.getDefault().getID());
}
}

If the default timezone that Java is using does not match your system timezone (the Linux date command is one way of checking), the JVM is not successfully detecting your system timezone.2、Solution
Under Linux, you can force Java to use a particular timezone by setting the

TZ

environment variable to an appropriate value. To set the

TZ

environment variable for all instances of thebash shell, create a shell script in the

/etc/profile.d

directory with a line similar to this:

export TZ="US/Eastern"

[Please note: All of the examples on this page use the

US/Eastern

timezone. Please substitute your timezone, as appropriate.]If your system does not support the

/etc/profile.d

directory, add the previous line to the

/etc/profile

initialization script.Under most versions of Linux, you can determine your system default timezone by checking where the symbolic link

/etc/localtime

points to by using the

ls -l /etc/localtime

command. The response will look something like this:

/etc/localtime -> /usr/share/zoneinfo/US/Eastern

The portion of the name after

/usr/share/zoneinfo/

is your

TZ

value.Any shell scripts that are started through

/etc/init.d

do not run the

/etc/profile

code. Therefore, any Java programs you start via

/etc/init.d

must have an explicit

export TZ="US/Eastern"

in order to work correctly.Once you have set the

TZ

variable (you must log out and log back in to see the change), it will become part of your shell environment. To check that you have successfully set the value of

TZ

, type the following command at your shell prompt:

echo $TZ

3、Alternatives
You can also force the use of a particular default timezone in Java either through programming or with a Java system property. The programming alternative is the least attractive as it requires that you change your Java programs by adding a line early in the program like this:

TimeZone.setDefault(TimeZone.getTimeZone("US/Eastern"))

To set the default timezone using a system property, set the

user.timezone

property to your time zone. One place to do this is on command line that starts your Java interpreter using the

-D

startup option, like this:

java -Duser.timezone=US/Eastern CLASS_NAME

While this last technique works, be forewarned that this property is not part of the Java specification.