Set default timezone in java

TimeZone represents a time zone offset, and also figures out daylight savings. Typically, you get a TimeZone using getDefault which creates a TimeZone based on the time zone where the program is running. For example, for a program running in Japan, getDefault creates a TimeZone object based on Japanese Standard Time. You can also get a TimeZone using getTimeZone along with a time zone ID. For instance, the time zone ID for the U.S. Pacific Time zone is «America/Los_Angeles». So, you can get a U.S. Pacific Time TimeZone object with:

TimeZone tz = TimeZone.getTimeZone("America/Los_Angeles");

You can use the getAvailableIDs method to iterate through all the supported time zone IDs. You can then choose a supported ID to get a TimeZone . If the time zone you want is not represented by one of the supported IDs, then a custom time zone ID can be specified to produce a TimeZone. The syntax of a custom time zone ID is:

CustomID: GMT Sign Hours : Minutes GMT Sign Hours Minutes GMT Sign Hours Sign: one of + - Hours: Digit Digit Digit Minutes: Digit Digit Digit: one of 0 1 2 3 4 5 6 7 8 9

Hours must be between 0 to 23 and Minutes must be between 00 to 59. For example, «GMT+10» and «GMT+0010» mean ten hours and ten minutes ahead of GMT, respectively. The format is locale independent and digits must be taken from the Basic Latin block of the Unicode standard. No daylight saving time transition schedule can be specified with a custom time zone ID. If the specified string doesn’t match the syntax, «GMT» is used. When creating a TimeZone , the specified custom time zone ID is normalized in the following syntax:

NormalizedCustomID: GMT Sign TwoDigitHours : Minutes Sign: one of + - TwoDigitHours: Digit Digit Minutes: Digit Digit Digit: one of 0 1 2 3 4 5 6 7 8 9

Three-letter time zone IDs

For compatibility with JDK 1.1.x, some other three-letter time zone IDs (such as «PST», «CTT», «AST») are also supported. However, their use is deprecated because the same abbreviation is often used for multiple time zones (for example, «CST» could be U.S. «Central Standard Time» and «China Standard Time»), and the Java platform can then only recognize one of them.

Field Summary

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Class TimeZone

Typically, you get a TimeZone using getDefault which creates a TimeZone based on the time zone where the program is running. For example, for a program running in Japan, getDefault creates a TimeZone object based on Japanese Standard Time.

You can also get a TimeZone using getTimeZone along with a time zone ID. For instance, the time zone ID for the U.S. Pacific Time zone is «America/Los_Angeles». So, you can get a U.S. Pacific Time TimeZone object with:

TimeZone tz = TimeZone.getTimeZone("America/Los_Angeles");

CustomID: GMT Sign Hours : Minutes GMT Sign Hours Minutes GMT Sign Hours Sign: one of + - Hours: Digit Digit Digit Minutes: Digit Digit Digit: one of 0 1 2 3 4 5 6 7 8 9

Hours must be between 0 to 23 and Minutes must be between 00 to 59. For example, «GMT+10» and «GMT+0010» mean ten hours and ten minutes ahead of GMT, respectively.

The format is locale independent and digits must be taken from the Basic Latin block of the Unicode standard. No daylight saving time transition schedule can be specified with a custom time zone ID. If the specified string doesn’t match the syntax, «GMT» is used.

When creating a TimeZone , the specified custom time zone ID is normalized in the following syntax:

NormalizedCustomID: GMT Sign TwoDigitHours : Minutes Sign: one of + - TwoDigitHours: Digit Digit Minutes: Digit Digit Digit: one of 0 1 2 3 4 5 6 7 8 9

Three-letter time zone IDs

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How to Set the JVM Time Zone

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1. Overview

The users of our applications can be demanding when it comes to timestamps. They expect our applications to detect their time zones automatically, and display timestamps in the correct time zone.

In this tutorial, we’ll take a look at several ways we can modify the time zone of the JVM. We’ll also learn about some of the pitfalls associated with managing the time zone.

2. Introduction to Time Zone

By default, the JVM reads time zone information from the operating system. This information gets passed to the TimeZone class, which stores the time zone and calculates the daylight saving time.

We can call the method getDefault, which will return the time zone where the program is running. Furthermore, we can obtain a list of supported time zone IDs from the application using TimeZone.getAvailableIDs().

When naming the time zone, Java relies on the naming convention of the tz database.

3. Changing the Time Zone

In this section, we’re going to take a look at several ways we can change the time zone in the JVM.

3.1. Setting an Environment Variable

Let’s begin by seeing how we can use an environment variable to change the time zone. We can add or modify an environment variable TZ.

For example, in Linux-based environments, we can use the export command:

export TZ="America/Sao_Paulo"

After setting the environment variable, we can see that the time zone of our running application is now America/Sao_Paulo:

Calendar calendar = Calendar.getInstance(); assertEquals(calendar.getTimeZone(), TimeZone.getTimeZone("America/Sao_Paulo"));

3.2. Setting a JVM Argument

An alternative to setting an environment variable is setting the JVM argument user.timezone. This JVM argument takes precedence over the environment variable TZ.

For example, we can use the flag -D when we run our application:

java -Duser.timezone="Asia/Kolkata" com.company.Main

Likewise, we can also set the JVM argument from the application:

System.setProperty("user.timezone", "Asia/Kolkata");

We can now see that the time zone is Asia/Kolkata:

Calendar calendar = Calendar.getInstance(); assertEquals(calendar.getTimeZone(), TimeZone.getTimeZone("Asia/Kolkata"));

3.3. Setting the Time Zone From the Application

Finally, we can also modify the JVM time zone from the application using the TimeZone class. This approach takes precedence over both the environment variable and the JVM argument.

Setting the default time zone is easy:

TimeZone.setDefault(TimeZone.getTimeZone("Portugal"));

As expected, the time zone is now Portugal:

Calendar calendar = Calendar.getInstance(); assertEquals(calendar.getTimeZone(), TimeZone.getTimeZone("Portugal"));

4. Pitfalls

4.1. Using Three-letter Time Zone IDs

Even though it’s possible to use three-letter IDs to represent the time zone, it’s not recommended.

Instead, we should use the longer names, as the three-letter IDs are ambiguous. For example, IST could be either India Standard Time, Irish Standard Time or Israel Standard Time.

4.2. Global Settings

Note that each of the above approaches is setting the timezone globally for the entire application. In modern applications, though, setting the timezone is often more nuanced than that.

For example, we probably need to translate time into the end user’s timezone, and so a global timezone wouldn’t make much sense. If a global timezone isn’t needed, consider specifying the time zone directly on each date-time instance. Either ZonedDateTime or OffsetDateTime is a handy class for this.

5. Conclusion

In this tutorial, we explained several ways to modify the time zone of the JVM. We saw that we could either set a system-wide environment variable, change a JVM argument or modify it programmatically from our application.

As usual, all the examples used in this article are available over on GitHub.

Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:

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