Is there any way to convert ZoneId to ZoneOffset in Java 8?

Question

I have an epoch second and a zoneId (see method1 below).

It can be convert to LocalDateTime with system default zoneId, but I don't find the way to convert epoch second to LocalDateTime (see method2 below), because there is no ZoneOffset.systemDefault. I think it's obscure.

import java.time.{Instant, LocalDateTime, ZoneId, ZoneOffset}

val epochSecond = System.currentTimeMillis() / 1000

// method1
LocalDateTime.ofInstant(Instant.ofEpochSecond(epochSecond), ZoneId.systemDefault())

// method2
LocalDateTime.ofEpochSecond(epochSecond, 0, ZoneOffset.MAX)

NOTE

The source code presented above is Scala.

What language/dialect are you using to make the bulk import `import java.time.{Instant, LocalDateTime, ZoneId, ZoneOffset}` work? It's an `unexpected token` for me in Java 11. — Snackoverflow, Feb 25 '19 at 10:10
I have discussed the theory behind `java.time` at length here: https://stackoverflow.com/a/56508200/145989 — Ondra Žižka, Jun 08 '19 at 17:57

Stanislav Bashkyrtsev · Accepted Answer · 2020-05-26T13:28:23.837

154

Here is how you can get ZoneOffset from ZoneId:

Instant instant = Instant.now(); //can be LocalDateTime
ZoneId systemZone = ZoneId.systemDefault(); // my timezone
ZoneOffset currentOffsetForMyZone = systemZone.getRules().getOffset(instant);

NB: ZoneId can have different offset depending on point in time and the history of the particular place. So choosing different Instants would result in different offsets.

NB2: ZoneId.of() can return a ZoneOffset instead of ZoneId if UTC+3/GMT+2/etc is passed as opposed to a time zone like Africa/Cairo. So if UTC/GMT offsets are passed then historical/geographical/daylight-saving information of the Instant won't be taken into account - you'll simply work with the specified offset.

edited May 26 '20 at 13:28

answered May 28 '16 at 16:43

Stanislav Bashkyrtsev

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This gives incorrect value if current instant is in DST, but at the moment of calculation it was without DST – msangel Apr 13 '20 at 13:11
I checked that and it works depending on another condition. Updated answer with that. – msangel Apr 14 '20 at 13:27

Basil Bourque · Answer 2 · 2021-05-24T15:41:28.953

tl;dr

ZonedDateTime.now( 
    ZoneId.of( "America/Montreal" ) 
)

…of current default time zone…

ZonedDateTime.now( 
    ZoneId.systemDefault() 
)

Details

The Answer by Stanislav Bshkyrtsev correctly and directly answers your Question.

But, there are larger issues involved, as suggested in the Answer by Jon Skeet.

`LocalDateTime`

I don't find the way to convert epoch second to LocalDateTime

LocalDateTime purposely has no concept of time zone or offset-from-UTC. Not likely what you want. The Local… means any locality, not any one particular locality. This class does not represent a moment, only potential moments along a range of about 26-27 hours (the range of time zones around the globe).

`Instant`

No need to start with epoch seconds if you are trying to get current time. Get the current 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).

Instant instant = Instant.now();

Inside of that Instant is a count of nanoseconds-from-epoch. But we do not really care.

See also, What's the difference between Instant and LocalDateTime?

`ZonedDateTime`

If you want to see that moment through the lens of a particular region’s wall-clock time, apply a ZoneId to get a ZonedDateTime.

ZoneId z = ZoneId.of( "Europe/Paris" );
ZonedDateTime zdt = instant.atZone( z );

As a shortcut, you can do directly to the ZonedDateTime.

ZonedDateTime zdt = ZonedDateTime.now( z );

A ZonedDateTime has an Instant within it. Call zdt.toInstant() to get the same moment in time as a basic value in UTC. Same number of nanoseconds-since-epoch either way, as a ZonedDateTime or as a Instant.

Seconds-since-epoch given

If you are given a count of seconds-since-epoch, and the epoch is the first moment of 1970 in UTC (1970-01-01T00:00:00Z), then feed that number to Instant.

long secondsSinceEpoch = 1_484_063_246L ;
Instant instant = Instant.ofEpochSecond( secondsSinceEpoch ) ;

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.

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 adds 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 bundle implementations of the java.time classes.
For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

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.

GeertPt · Answer 3 · 2015-09-17T09:59:38.987

47

There is no one-to-one mapping. A ZoneId defines a geographic extent in which a set of different ZoneOffsets is used over time. If the timezone uses daylight saving time, its ZoneOffset will be different between summer and winter.

Furthermore, the daylight saving time rules may have changed over time, so the ZoneOffset could be different for e.g. 13/10/2015 compared to 13/10/1980.

So you can only find the ZoneOffset for a ZoneId on a particular Instant.

See also https://en.wikipedia.org/wiki/Tz_database

edited Sep 17 '15 at 09:59

answered Sep 17 '15 at 09:41

GeertPt

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I know that, but how is it done?If I know the LocaDate and have a ZoneId, how do I convert it into a ZoneOffset. My use-case is a string that contains a time and a zone. I want to parse the string into an OffsetTime, without droping the zone information. – Kai Moritz Dec 01 '15 at 08:26

score 11 · Answer 4 · answered Sep 17 '15 at 09:29

As the documentation says, "This is primarily intended for low-level conversions rather than general application usage."

Going via Instant makes perfect sense to me - your epoch second is effectively a different representation of an Instant, so convert to an Instant and then convert that into a particular time zone.

score 9 · Answer 5 · answered Mar 16 '17 at 19:12

I hope the first two lines of my solution below are helpful. My problem was I had a LocalDateTime and the name of a time zone, and I needed an instant so I could build a java.util.Date, because that's what MongoDB wanted. My code is Scala, but it's so close to Java here I think there should be no problem understanding it:

val zid = ZoneId.of(tzName)                                // "America/Los_Angeles"
val zo: ZoneOffset = zid.getRules.getOffset(localDateTime) // ⇒ -07:00
                                         // 2017-03-16T18:03

val odt = OffsetDateTime.of(localDateTime, zo) // ⇒ 2017-03-16T18:03:00-07:00
val instant = odt.toInstant                    // ⇒ 2017-03-17T01:03:00Z
val issued = Date.from(instant)

I posted this answer here because this was the page that came up when I was searching for a way to do what I eventually figured out. — gknauth, Mar 16 '17 at 19:15

score 3 · Answer 6 · edited Nov 16 '18 at 15:39

3

The following returns the amount of time in milliseconds to add to UTC to get standard time in this time zone:

TimeZone.getTimeZone(ZoneId.of("Europe/Amsterdam")).getRawOffset()

edited Nov 16 '18 at 15:39

pheeleeppoo

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answered Jan 05 '18 at 10:12

Jelmer

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localZoneOffset = ZoneOffset.ofTotalSeconds(TimeZone.getTimeZone(localTimeZone).getRawOffset / 1000) – Vitamon Mar 26 '21 at 13:32

score 3 · Answer 7 · answered Aug 16 '20 at 22:11

I have an epoch second and a zoneId. Is there any way to convert ZoneId to ZoneOffset in java 8?

Get ZonedDateTime from epoch second and Zone Id
Get ZoneOffset from ZonedDateTime

Demo:

import java.time.Instant;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;

public class Main {
    public static void main(String[] args) {
        // Get ZonedDateTime from epoch second and Zone Id
        ZonedDateTime zdt = Instant.ofEpochSecond(1597615462L).atZone(ZoneId.of("Europe/London"));

        // Get ZoneOffset from ZonedDateTime
        ZoneOffset offset = zdt.getOffset();

        System.out.println(offset);
    }
}

Output:

+01:00

score 0 · Answer 8 · answered Oct 12 '21 at 11:49

0

Since you are looking for the default zone offset

ZonedDateTime.now().getOffset()

answered Oct 12 '21 at 11:49

abbas

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score 0 · Answer 9 · answered Dec 11 '21 at 12:14

This does it without creating an Instant or such objects to pull it out.

public static ZoneOffset offset() {
    return offset(ZoneId.systemDefault());                 // Default system zone id
}
public static ZoneOffset offset(ZoneId id) {
    return ZoneOffset.ofTotalSeconds((int) 
        TimeUnit.MILLISECONDS.toSeconds(
            TimeZone.getTimeZone(id).getRawOffset()        // Returns offset in milliseconds 
        )
    );
}

score 0 · Answer 10 · answered Aug 11 '22 at 15:20

Here is what we use. First convert zone id to timezone, then get the offset in millis, then convert to seconds, then create a ZoneOffset.

public static final ZoneOffset toOffset(ZoneId zoneId) {
    return Optional.ofNullable(zoneId)
            .map(TimeZone::getTimeZone)
            .map(TimeZone::getRawOffset)
            .map(Duration::ofMillis)
            .map(Duration::getSeconds)
            .map(Number::intValue)
            .map(ZoneOffset::ofTotalSeconds)
            .orElse(null);
}