java - JodaTime - how to get current time in UTC

Question

I want to get the current time in UTC. What I do so far is following (just for testing purposes):

    DateTime dt = new DateTime();
    DateTimeZone tz = DateTimeZone.getDefault();
    LocalDateTime nowLocal = new LocalDateTime();
    DateTime nowUTC = nowLocal.toDateTime(DateTimeZone.UTC);

    Date d1 = nowLocal.toDate();
    Date d2 = nowUTC.toDate();

    L.d("tz: " + tz.toString());
    L.d("local: " + d1.toString());
    L.d("utc: " + d2.toString());

• d1 is my local time, that's fine
• d2 is my local time + 1, but should be local time - 1...

My local time zone is UTC+1 (according to the debug output and the list here: https://www.joda.org/joda-time/timezones.html)...

How do I correctly convert from one time zone to another (inclusive the millisecond representation)?

EDIT

I need the date/milliseconds... It's NOT about displaying the time correctly....

EDIT 2

Now, with the help of a comment and an answer, I tried following:

    DateTimeZone tz = DateTimeZone.getDefault();
    DateTime nowLocal = new DateTime();
    LocalDateTime nowUTC = nowLocal.withZone(DateTimeZone.UTC).toLocalDateTime();
    DateTime nowUTC2 = nowLocal.withZone(DateTimeZone.UTC);

    Date dLocal = nowLocal.toDate();
    Date dUTC = nowUTC.toDate();
    Date dUTC2 = nowUTC2.toDate();

    L.d(Temp.class, "------------------------");
    L.d(Temp.class, "tz    : " + tz.toString());
    L.d(Temp.class, "local : " + nowLocal +     " | " + dLocal.toString());
    L.d(Temp.class, "utc   : " + nowUTC +       " | " + dUTC.toString()); // <= WORKING SOLUTION
    L.d(Temp.class, "utc2  : " + nowUTC2 +      " | " + dUTC2.toString());

OUTPUT

tz    : Europe/Belgrade
local : 2015-01-02T15:31:38.241+01:00 | Fri Jan 02 15:31:38 MEZ 2015
utc   : 2015-01-02T14:31:38.241 | Fri Jan 02 14:31:38 MEZ 2015
utc2  : 2015-01-02T14:31:38.241Z | Fri Jan 02 15:31:38 MEZ 2015

What I wanted was, that the local date displays 15 o'clock and utc date displays 14 o'clock... For now, this seems to work...

----- EDIT3 - Final solution -----

Hopefully, this is a good solution... I think, i respects all tipps i got...

    DateTimeZone tz = DateTimeZone.getDefault();
    DateTime nowUTC = new DateTime(DateTimeZone.UTC);
    DateTime nowLocal = nowUTC.withZone(tz);

    // This will generate DIFFERENT Dates!!! As I want it!
    Date dLocal = nowLocal.toLocalDateTime().toDate();
    Date dUTC = nowUTC.toLocalDateTime().toDate();

    L.d("tz    : " + tz.toString());
    L.d("local : " + nowLocal +     " | " + dLocal.toString());
    L.d("utc   : " + nowUTC +       " | " + dUTC.toString());

Output:

tz    : Europe/Belgrade
local : 2015-01-03T21:15:35.170+01:00 | Sat Jan 03 21:15:35 MEZ 2015
utc   : 2015-01-03T20:15:35.170Z | Sat Jan 03 20:15:35 MEZ 2015

Answer 1

You're making it far more complicated than you need to:

DateTime dt = new DateTime(DateTimeZone.UTC);

No conversion required at all. If you find you actually need to convert, you can use withZone. I'd suggest you avoid going via LocalDateTime, however, as that way you can lose information due to time zone transitions (two different instants can have the same local time in the same time zone, because clocks go back and repeat local time.

Having said all of this, for the sake of testability I personally like using a Clock interface which allows me to get the current time (e.g. as an Instant). You can then use dependency injection to inject a real system clock when running in production, and a fake clock with a preset time for tests. Java 8's java.time package has this idea built into it, btw.