Java: Adding TimeZone to DateTimeFormatter

Question

The LocalDateTime API gives the possibility to add the TimeZone Name by using the key \"z\" in the formatter. I get an exception adding this key and don\'t understand why. I

Answer 1

LocalDateTime has two fields of type LocalDate and LocalTime.
LocalDate has fields day, month, and year.
LocalTime has fields hour, minute, second, and nano.

Nowhere in that is a time zone given. Which is by nature, since the javadoc of LocalDateTime says:

A date-time without a time-zone

So, if the "local" date/time value is already representing a time in UTC, and you want it formatted saying so, you have multiple options:

• Change the LocalDateTime to a ZonedDateTime by calling atZone():

  System.out.println(time.atZone(ZoneOffset.UTC)
                         .format(DateTimeFormatter.ofPattern("hh:mm:ss a z")));
  

• Specify an override time zone in the formatter by calling withZone():

  System.out.println(time.format(DateTimeFormatter.ofPattern("hh:mm:ss a z")
                                                  .withZone(ZoneOffset.UTC)));
  

• Format with a literal Z character:

  System.out.println(time.format(DateTimeFormatter.ofPattern("hh:mm:ss a 'Z'")));
  

All three of the above outputs:

11:59:22 PM Z

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Now, if the "local" date/time is really in a different time zone, you can use either of the first two, and just specify the actual zone.

E.g. if time zone is -04:00, use ZoneOffset.ofHours(-4), and you'll get:

11:59:22 PM -04:00

Or if you are in New York, use ZoneId.of("America/New_York"), and you'll get:

11:59:22 PM EDT

If the "local" date/time is for New York, but you want formatted text to be UTC, use both at the same time, i.e.

System.out.println(time.atZone(ZoneId.of("America/New_York"))
                       .format(DateTimeFormatter.ofPattern("hh:mm:ss a z")
                                                .withZone(ZoneOffset.UTC)));

With that, you get the time converted to:

03:59:22 AM Z