Get TimeZone offset value from TimeZone without TimeZone name

Question

I need to save the phone's timezone in the format [+/-]hh:mm

I am using TimeZone class to deal with this, but the only format I can get is the following:

PST -05:00
GMT +02:00

I would rather not substring the result, is there any key or option flag I can set to only get the value and not the name of that timezone (GMT/CET/PST...)?

Answer 1

I need to save the phone's timezone in the format [+/-]hh:mm

No, you don't. Offset on its own is not enough, you need to store the whole time zone name/id. For example I live in Oslo where my current offset is +02:00 but in winter (due to dst ) it is +01:00. The exact switch between standard and summer time depends on factors you don't want to explore.

So instead of storing + 02:00 (or should it be + 01:00 ?) I store "Europe/Oslo" in my database. Now I can restore full configuration using:

TimeZone tz = TimeZone.getTimeZone("Europe/Oslo")

Want to know what is my time zone offset today?

tz.getOffset(new Date().getTime()) / 1000 / 60   //yields +120 minutes

However the same in December:

Calendar christmas = new GregorianCalendar(2012, DECEMBER, 25);
tz.getOffset(christmas.getTimeInMillis()) / 1000 / 60   //yields +60 minutes

Enough to say: store time zone name or id and every time you want to display a date, check what is the current offset (today) rather than storing fixed value. You can use TimeZone.getAvailableIDs() to enumerate all supported timezone IDs.

Answer 2

@MrBean - I was in a similar situation where I had to call a 3rd-party web service and pass in the Android device's current timezone offset in the format +/-hh:mm. Here is my solution:

public static String getCurrentTimezoneOffset() {

    TimeZone tz = TimeZone.getDefault();  
    Calendar cal = GregorianCalendar.getInstance(tz);
    int offsetInMillis = tz.getOffset(cal.getTimeInMillis());

    String offset = String.format("%02d:%02d", Math.abs(offsetInMillis / 3600000), Math.abs((offsetInMillis / 60000) % 60));
    offset = (offsetInMillis >= 0 ? "+" : "-") + offset;

    return offset;
} 

Answer 3

With Java 8 now, you can use:

Integer offset  = ZonedDateTime.now().getOffset().getTotalSeconds();

to get the current system time offset from UTC. Then you can convert it to any format you want. Found it useful for my case.

Example: https://docs.oracle.com/javase/tutorial/datetime/iso/timezones.html

Answer 4

With Java 8, you can achieve this with the following code:

TimeZone tz = TimeZone.getDefault();
String offsetId = tz.toZoneId().getRules().getStandardOffset(Instant.now()).getId();

and the offsetId will be something like +01:00 .

Please notice the function getStandardOffset() needs an Instant as parameter. It is the specific time point, at which you want to check the offset of given timezone, as timezone's offset may vary during time . For the reason of some areas have Daylight Saving Time .

I think it is the reason why @Tomasz Nurkiewicz recommands not to store offset in signed hour format directly, but to check the offset each time you need it.

Answer 5

ZoneId here = ZoneId.of("Europe/Kiev");
ZonedDateTime hereAndNow = Instant.now().atZone(here);
String.format("%tz", hereAndNow);

will give you a standardized string representation like "+0300"

Answer 6

We can easily get the millisecond offset of a TimeZone with only a TimeZone instance and System.currentTimeMillis() . Then we can convert from milliseconds to any time unit of choice using the TimeUnit class.

Like so:

public static int getOffsetHours(TimeZone timeZone) {
    return (int) TimeUnit.MILLISECONDS.toHours(timeZone.getOffset(System.currentTimeMillis()));
}

Or if you prefer the new Java 8 time API

public static ZoneOffset getOffset(TimeZone timeZone) { //for using ZoneOffsett class
    ZoneId zi = timeZone.toZoneId();
    ZoneRules zr = zi.getRules();
    return zr.getOffset(LocalDateTime.now());
}

public static int getOffsetHours(TimeZone timeZone) { //just hour offset
    ZoneOffset zo = getOffset(timeZone);
    TimeUnit.SECONDS.toHours(zo.getTotalSeconds());
}

Answer 7

java.time : the modern date-time API

You can get the offset of a timezone using ZonedDateTime#getOffset .

Note that the offset of a timezone that observes DST changes as per the changes in DST. For other places (eg India), it remains fixed. Therefore, it is recommended to mention the moment when the offset of a timezone is shown. A moment is mentioned as Instant.now() and it represents the date-time in UTC (represented by Z which stands for Zulu and specifies the timezone offset of +00:00 hours).

Display offset of all timezones returned by ZoneId.getAvailableZoneIds() :

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

public class Main {
    public static void main(String[] args) {
        // Test
        Instant instant = Instant.now();
        System.out.println("Timezone offset at " + instant);
        System.out.println("==============================================");
        ZoneId.getAvailableZoneIds()
            .stream()
            .sorted()
            .forEach(strZoneId -> System.out.printf("%-35s: %-6s%n",
                strZoneId, getTzOffsetString(ZoneId.of(strZoneId), instant)));
    }

    static String getTzOffsetString(ZoneId zoneId, Instant instant) {
        return ZonedDateTime.ofInstant(instant, zoneId).getOffset().toString();
    }
}

Output:

Timezone offset at 2021-05-05T21:45:34.150901Z
==============================================
Africa/Abidjan                     : Z     
Africa/Accra                       : Z     
Africa/Addis_Ababa                 : +03:00
...
...
...    
W-SU                               : +03:00
WET                                : +01:00
Zulu                               : Z  

Learn more about the the modern date-time API ^* from Trail: Date Time .

---

^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project .}

Answer 8

I know this is old, but I figured I'd give my input. I had to do this for a project at work and this was my solution.

I have a Building object that includes the Timezone using the TimeZone class and wanted to create zoneId and offset fields in a new class.

So what I did was create:

private String timeZoneId;
private String timeZoneOffset;

Then in the constructor I passed in the Building object and set these fields like so:

this.timeZoneId = building.getTimeZone().getID();
this.timeZoneOffset = building.getTimeZone().toZoneId().getId();

So timeZoneId might equal something like "EST" And timeZoneOffset might equal something like "-05:00"

I would like to not that you might not