Get TimeZone offset value from TimeZone without Ti

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

With java8 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 3

@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 4

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 5

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

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(so.getTotalSeconds());
}