How to transfer date and time from one time zone to another when changing the date?

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I'm new to working with dates, times and timezones in java, so don't judge strictly). I am developing an application that writes messages to the database at the current date. But there is a situation when a message may come to me from a different timezone and, accordingly, this is a different time and it will not coincide with my time, which I send to the database.

I receive the value "2021-07-28 15:30:00 Europe / Minsk" - date-time with timezone (It can also come in UTC), "Asia / Kamchatka" - timezone into which the date and time should be converted. I want to know the DATE "2021-07-28 15:30:00 Asia / Kamchatka" in the timezone "Europe/Minsk".

The catch is that there is a situation when, when adding time in the time zone (Asia/Kamchatka) 2021-07-28 15: 30: 00 + 9 = 2021-07-29 00:30. I need to get a DATE after all calculations without time.

localdate calendar timezone date java
1 Answers

I want to know the DATE "2021-07-28 15:30:00 Asia / Kamchatka" in the timezone "Europe / Minsk".

You can use ZonedDateTime#withZoneSameInstant to meet this requirement.

The catch is that there is a situation when, when adding time in the time zone (Asia / Kamchatka) 2021-07-28 15: 30: 00 + 9 = 2021-07-29 00:30. I need to get DATE after all calculations without time.

You can use ZonedDateTime#toLocalDate to meet this requirement.

Demo:

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 z", Locale.ENGLISH);
        String strDateTime = "2021-07-28 15:30:00 Asia/Kamchatka";
        ZonedDateTime zdtInput = ZonedDateTime.parse(strDateTime, dtf);
        ZonedDateTime zdtOuput = zdtInput.withZoneSameInstant(ZoneId.of("Europe/Minsk"));
        System.out.println(zdtInput);
        System.out.println(zdtOuput);
        System.out.println(zdtOuput.toLocalDate());
    }
}

Output:

2021-07-28T15:30+12:00[Asia/Kamchatka]
2021-07-28T06:30+03:00[Europe/Minsk]
2021-07-28

ONLINE DEMO

Learn more about the modern Date-Time API from Trail: Date Time.

Note: Quoted below is a valuable comment by Basil Bourque:

The example data in Question shows time zone names incorrectly spelled with a SPACE character on each side of the slash. I suggest you add a bit of code using String#replace to substitute the single character "/" for triple character " / " before parsing.

If it is the case, before parsing the date-time string, you need to remove the whitespace characters before and after the / separator. You can do so as follows:

String strDateTime = "2021-07-28 15:30:00 Asia / Kamchatka";
strDateTime = strDateTime.replaceAll("\\s+/\\s+", "/");

Rest of the code will work as it is.

user_108195730
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