Java TimeZone.getTimeZone("PDT") not working

Question

It returns the default timezone for GMT.

Using the SimpleTimeFormat with "z" for timezone, it prints "PDT". But "PDT" is not in the list returned from TimeZone.getAvailableIDs(). Really strange!

Anyone knows why "PDT" is not a standard tz? How to deal with this? Someone invokes my API passing in "PDT" as the timezone. Thanks.

Answer 1

PDT is not a time zone

Anyone knows why "PDT" is not a standard tz?

Because “PDT” is not a time zone!

The “PDT” is a pseudo-time zone used by the media to indicate vaguely a set of time zones plus an indicator if they intended during the period when Daylight Saving Time (DST) is engaged or not (PST). Avoid these 2-4 letter codes as they are not true time zones, not standardized, and are not even unique(!).

Proper time zone names

Specify a proper time zone name in the format of continent/region, such as America/Montreal, Africa/Casablanca, or Pacific/Auckland.

By PDT any of these time zones, and more, may be intended:

ZoneId z = ZoneId.of( "America/Los_Angeles" ) ;
ZoneId z = ZoneId.of( "America/Tijuana" ) ;
ZoneId z = ZoneId.of( "America/Whitehorse" ) ;

But PDT might not mean this zone as Arizona does not participate in the Daylight Saving Time (DST) nonsense, and the D in the middle means DST.

ZoneId z = ZoneId.of( "America/Phoenix" ) ;

Avoid legacy date-time classes

Avoid SimpleTimeFormat class as it is a part of the troublesome old date-time classes that are now legacy, supplanted by the java.time classes. Use DateTimeFormatter instead.

Avoid TimeZone as well. Replaced by ZoneId.

Pass ZoneId, not string

Someone invokes my API passing in "PDT" as the timezone.

Change your API to take a ZoneId as an argument, rather than a mere String. That ensures valid values and gives you type-safety.

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes. Hibernate 5 & JPA 2.2 support java.time.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later - Part of the standard Java API with a bundled implementation.
  • Java 9 brought some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android (26+) bundle implementations of the java.time classes.
  • For earlier Android (<26), the process of API desugaring brings a subset of the java.time functionality not originally built into Android.
    • If the desugaring does not offer what you need, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above) to Android. See How to use ThreeTenABP….

Answer 2

"PDT" is an abbreviation for Pacific Daylight Time. It is used in conjunction with Pacific Standard Time to make up the Pacific time zone.

The time zone identifier for the Pacific time zone is "America/Los_Angeles". You should use that instead.

Read the timezone tag wiki, and Wikipedia's article on the tz database.