How do I display a date with a custom timezone?

Question

Lets say I have a string that represents a date that looks like this:

"Wed Jul 08 17:08:48 GMT 2009"

So I parse that string into a date object like this:

DateFormat formatter = new SimpleDateFormat("EEE MMM dd HH:mm:ss ZZZ yyyy");
Date fromDate = (Date)formatter.parse(fromDateString);

That gives me the correct date object. Now I want to display this date as a CDT value.

I've tried many things, and I just can't get it to work correctly. There must be a simple method using the DateFormat class to get this to work. Any advice? My last attempt was this:

formatter.setTimeZone(toTimeZone);
String result = formatter.format(fromDate);

Answer 1

Use "zzz" instead of "ZZZ": "Z" is the symbol for an RFC822 time zone.

DateFormat formatter = new SimpleDateFormat("EEE MMM dd HH:mm:ss zzz yyyy");

Having said that, my standard advice on date/time stuff is to use Joda Time, which is an altogether better API.

EDIT: Short but complete program:

import java.text.*;
import java.util.*;

public class Test
{
    public List<String> names;

    public static void main(String [] args)
        throws Exception // Just for simplicity!
    {
        String fromDateString = "Wed Jul 08 17:08:48 GMT 2009";
        DateFormat formatter = new SimpleDateFormat
            ("EEE MMM dd HH:mm:ss zzz yyyy");
        Date fromDate = (Date)formatter.parse(fromDateString);
        TimeZone central = TimeZone.getTimeZone("America/Chicago");
        formatter.setTimeZone(central);
        System.out.println(formatter.format(fromDate));
    }
}

Output: Wed Jul 08 12:08:48 CDT 2009

Answer 2

Using:

formatter.setTimeZone(TimeZone.getTimeZone("US/Central"));

outputs:

Wed Jul 08 12:08:48 CDT 2009

for the date in your example on my machine. That is after substituting zzz for ZZZ in the format string.

Answer 3

Sorry for digging out an old-thread. But I was wondering if there is a java-class that holds all the time-zone-ids as a constant class. So instead of having to hard-code the time-zone-id while setting time-zone like this:

formatter.setTimeZone(TimeZone.getTimeZone("US/Central"));

we would instead be doing something more standard/uniform:

formatter.setTimeZone(TimeZone.getTimeZone(SomeConstantClass.US_CENTRAL)); 

where SomeConstantClass.java is a class that holds the constants referring to the different time-zone-ids that are supported by the TimeZone class.

Answer 4

The modern way is with the java.time classes.

ZonedDateTime

Specify a formatting pattern to match your input string. The codes are similar to SimpleDateFormat but not exactly. Be sure to read the class doc for DateTimeFormatter. Note that we specify a Locale to determine what human language to use for name of day-of-week and name of month.

String input = "Wed Jul 08 17:08:48 GMT 2009";
DateTimeFormatter f = DateTimeFormatter.ofPattern ( "EEE MMM dd HH:mm:ss z uuuu" , Locale.ENGLISH );
ZonedDateTime zdt = ZonedDateTime.parse ( input , f );

zdt.toString(): 2009-07-08T17:08:48Z[GMT]

We can adjust that into any other time zone.

Specify a proper time zone name in the format of continent/region. Never use the 3-4 letter abbreviation such as CDT or EST or IST as they are not true time zones, not standardized, and not even unique(!).

I will guess that by CDT you meant a time zone like America/Chicago.

ZoneId z = ZoneId.of( "America/Chicago" );
ZonedDateTime zdtChicago = zdt.withZoneSameInstant( z );

zdtChicago.toString() 2009-07-08T12:08:48-05:00[America/Chicago]

Instant

Generally best to work in UTC. For that extract an Instant. The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).

This Instant class is a basic building-block class of java.time. You can think of ZonedDateTime as an Instant plus a ZoneId.

Instant instant = zdtChicago.toInstant();

instant.toString(): 2009-07-08T17:08:48Z

---

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, & java.text.SimpleDateFormat.

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

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

Where to obtain the java.time classes?

• Java SE 8 and SE 9 and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • See How to use….

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.