Java – ZonedDateTime does not correctly convert to Date object?

I have the following Java code:

Date convertedDate = Date.from(zonedDateTime.toInstant());

The Issue I am having is that convertedDateis not correct in comparison to the zonedDateTime object.

For Example when I have a zonedDateTime object of:

2021-09-16T12:00

with zone:

Africa/Abidjan

The code above converts this to:

Thu Sep 16 13:00:00 BST 2021

What I would be expecting here is

 Thu Sep 16 10:00:00 BST 2021

As the Africa/Abidjan timezone is 2 hours ahead of BST.

How can I solve this?

Answer

java.time

The java.util Date-Time API and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern Date-Time API^*.

Solution using java.time, the modern Date-Time API:

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;

public class Main {
    public static void main(String[] args) {
        // The given ZonedDateTime
        ZonedDateTime zdtAbidjan = ZonedDateTime.of(
                                        LocalDateTime.of(LocalDate.of(2021, 9, 16),
                                        LocalTime.of(12, 0)),
                                        ZoneId.of("Africa/Abidjan")
                                    );
        System.out.println(zdtAbidjan);

        ZonedDateTime zdtLondon = zdtAbidjan.withZoneSameInstant(ZoneId.of("Europe/London"));
        System.out.println(zdtLondon);
    }
}

Output:

2021-09-16T12:00Z[Africa/Abidjan]
2021-09-16T13:00+01:00[Europe/London]

ONLINE DEMO

• The Z in the output is the timezone designator for zero-timezone offset. It stands for Zulu and specifies the Etc/UTC timezone (which has the timezone offset of +00:00 hours).

• From the output, it is clear that 2021-09-16T12:00Z[Africa/Abidjan] is equal to 2021-09-16T13:00+01:00[Europe/London].

Learn more about 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.}