Convert date from GMT timezone to local time zone -- using ISO_OFFSET_DATE_TIME

Question

I have a date, assumed to be in GMT, which I want to convert to local time zone using the ISO_OFFSET_DATE_TIME formatting.

Basically, I want to go from:

2018-03-13 03:00:00.0

to:

2018-03-13T00:00:00-09:00

Obviously this would change, depending on your local time zone.

Any ideas on how I could do this?

Answer 1

You can leverage ZonedDateTime for this. You just need to read in the date as UTC and convert it as needed. You might get something like this:

String readPattern = "yyyy-MM-dd HH:mm:ss.S";
DateTimeFormatter readDateTimeFormatter = DateTimeFormatter.ofPattern(readPattern).withZone(ZoneOffset.UTC);
LocalDateTime utcLocalDateTime = LocalDateTime.parse("2018-03-13 03:00:00.0", readDateTimeFormatter);
ZonedDateTime localZonedDateTime = utcLocalDateTime.atOffset(ZoneOffset.UTC).atZoneSameInstant(ZoneId.systemDefault());
String writePattern = "yyyy-MM-dd HH:mm:ssXXX";
DateTimeFormatter writeDateTimeFormatter = DateTimeFormatter.ofPattern(writePattern);
System.out.println(writeDateTimeFormatter.format(localZonedDateTime));

For more info, see:

• https://docs.oracle.com/javase/8/docs/api/java/time/ZonedDateTime.html
• https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html

Answer 2

Parse the date-time string into LocalDateTime :

DateTimeFormatter dtf = DateTimeFormatter.ofPattern("u-M-d H:m:s.S", Locale.ENGLISH);
LocalDateTime ldt = LocalDateTime.parse("2018-03-13 03:00:00.0", dtf);

Combine this with UTC offset to create an OffsetDateTime :

OffsetDateTime odtUtc = ldt.atOffset(ZoneOffset.UTC);

Create its copy with offset set as -09:00 while keeping the instant same:

OffsetDateTime odtUtcMinus9 = odtUtc.withOffsetSameInstant(ZoneOffset.of("+09:00"));

Demo:

import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("u-M-d H:m:s.S", Locale.ENGLISH);
        LocalDateTime ldt = LocalDateTime.parse("2018-03-13 03:00:00.0", dtf);
        System.out.println(ldt); // 2018-03-13T03:00

        OffsetDateTime odtUtc = ldt.atOffset(ZoneOffset.UTC);
        System.out.println(odtUtc); // 2018-03-13T03:00Z

        OffsetDateTime odtUtcMinus9 = odtUtc.withOffsetSameInstant(ZoneOffset.of("+09:00"));
        System.out.println(odtUtcMinus9); // 2018-03-13T12:00+09:00
    }
}

Note that the timezone offset is a fixed thing ie it is independent of the DST . If you are looking for an automatic adjustment of timezone offset as per the DST, use ZonedDateTime . The methods are very much similar to what we have used in the last demo.

Demo:

import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("u-M-d H:m:s.S", Locale.ENGLISH);
        LocalDateTime ldt = LocalDateTime.parse("2018-03-13 03:00:00.0", dtf);
        System.out.println(ldt); // 2018-03-13T03:00

        ZonedDateTime zdtUtc = ldt.atZone(ZoneId.of("Etc/UTC"));
        System.out.println(zdtUtc); // 2018-03-13T03:00Z[Etc/UTC]

        ZonedDateTime zdtAmericaAdak = zdtUtc.withZoneSameInstant(ZoneId.of("America/Adak"));
        System.out.println(zdtAmericaAdak); // 2018-03-12T18:00-09:00[America/Adak]

        // A custom format
        DateTimeFormatter dtfOutput = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss.SSSXXX", Locale.ENGLISH);
        String formatted = dtfOutput.format(zdtAmericaAdak);
        System.out.println(formatted); // 2018-03-12 18:00:00.000-09:00
    }
}   

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

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^{* 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 .}