Convert UTC datetime to local datetime using java.time-CodePudding

I have a UTC date-time like this (a String): 2022-11-22T17:15:00

And a ZoneID like this: "America/Tijuana"

Using java.time API, I want to get the actual datetime for that zone, which is: 2022-11-22T09:15:00 (the time is 09:15 instead of 17:15)

ZonedDateTime.toLocalDateTime() returns: 2022-11-22T17:15
ZonedDateTime.toString() returns: 2022-11-22T17:15-08:00[America/Tijuana]

None of the above gives me what I'm looking for.

This is my code:

    ZoneId zonaID = ZoneId.of('America/Tijuana');
    CharSequence dateUTC = "2022-11-22T17:15:00";
    LocalDateTime dateTimeL = LocalDateTime.parse(dateUTC);
    ZonedDateTime myZDT = ZonedDateTime.now();
    ZonedDateTime myZDTFinal = myZDT.of(dateTimeL, zonaID);
    System.out.println("using toLocalDateTime: "   myZDTFinal.toLocalDateTime());
    System.out.println("using toString: "   myZDTFinal.toString());

I know that this might be a duplicated question but there's so many questions about date-times and I just haven't been able to figure out this.

Any help will be really appreciated.

CodePudding user response：

You have to convert your date to UTC, then convert the convert this zone to your expected zone using withZoneSameInstant like this:

ZonedDateTime toUTCZone  = ZonedDateTime.of(dateTimeL, ZoneOffset.UTC);
ZonedDateTime myZDTFinal = toUTCZone.withZoneSameInstant(zonaID);

Output

2022-11-22T09:15-08:00[America/Tijuana]

CodePudding user response：

`ZonedDateTime#withZoneSameInstant`

Use it to convert a ZonedDateTime into another ZonedDateTime of the corresponding ZoneId.

Finally, get the LocalDateTime out of the ZonedDateTime by using ZonedDateTime#toLocalDateTime.

LocalDateTime
    .parse("2022-11-22T17:15:00") // Parse the given date-time string into LocalDateTime
    .atZone(ZoneOffset.UTC) // Convert it into a ZonedDateTime 
    .withZoneSameInstant(ZoneId.of("America/Tijuana")) // Convert the result into a ZonedDateTime at another time-zome
    .toLocalDateTime() // Convert the result into LocalDateTime

Demo:

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

public class Main {
    public static void main(String[] args) {
        LocalDateTime ldtInTijuana = LocalDateTime.parse("2022-11-22T17:15:00")
                .atZone(ZoneOffset.UTC)
                .withZoneSameInstant(ZoneId.of("America/Tijuana"))
                .toLocalDateTime();
        System.out.println(ldtInTijuana);

        // Custom format
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuu-MM-dd'T'HH:mm:ss", Locale.ENGLISH);
        String formatted = ldtInTijuana.format(formatter);
        System.out.println(formatted);
    }
}

Output:

2022-11-22T09:15
2022-11-22T09:15:00

Note that LocalDateTime#toString removes second and fraction-of-second values if they are zero. If you want to keep them (as you have posted in your question), you can do so by using a DateTimeFormatter as shown above.

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