Java 8 examples to show you how to convert from Instant to ZonedDateTime

1. Instant -> ZonedDateTime

Example to convert a Instant UTC+0 to a Japan ZonedDateTime UTC+9

package com.mkyong.date;

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

public class InstantZonedDateTime1 {

    public static void main(String[] argv) {

        // Z = UTC+0
        Instant instant = Instant.now();

        System.out.println("Instant : " + instant);

        // Japan = UTC+9
        ZonedDateTime jpTime = instant.atZone(ZoneId.of("Asia/Tokyo"));

        System.out.println("ZonedDateTime : " + jpTime);

        System.out.println("OffSet : " + jpTime.getOffset());

    }

}

Output

Instant : 2016-08-18T06:17:10.225Z
LocalDateTime : 2016-08-18T06:17:10.225

2. ZonedDateTime -> Instant

Convert the Japan ZonedDateTime UTC+9 back to a Instant UTC+0/Z, review the result, the offset is taken care automatically.

package com.mkyong.date;

import java.time.*;

public class InstantZonedDateTime2 {

    public static void main(String[] argv) {

        LocalDateTime dateTime = LocalDateTime.of(2016, Month.AUGUST, 18, 6, 57, 38);

        // UTC+9
        ZonedDateTime jpTime = dateTime.atZone(ZoneId.of("Asia/Tokyo"));

        System.out.println("ZonedDateTime : " + jpTime);

        // Convert to instant UTC+0/Z , java.time helps to reduce 9 hours
        Instant instant = jpTime.toInstant();

        System.out.println("Instant : " + instant);

    }

}

Output

ZonedDateTime : 2016-08-18T06:57:38+09:00[Asia/Tokyo]
Instant : 2016-08-17T21:57:38Z

References

1. Wikipedia – ISO 8601 date format
2. Instant JavaDoc
3. ZoneddateTime JavaDoc

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