How do I convert LocalDate to ZonedDateTime?

By Wayan in Java 8, Java Date Time API 0 Comment

You can use the atStartOfDay() method from LocalDate class to convert a LocalDate into a LocalDateTime. Then, you need to convert LocalDateTime to a ZonedDateTime using the atZone() method.

Here is an example:

package org.kodejava.datetime;

import java.time.*;

public class LocalDateToZonedDateTimeExample {
    public static void main(String[] args) {
        // Create a LocalDate
        LocalDate date = LocalDate.of(2023, Month.JULY, 9);
        System.out.println("LocalDate: " + date);

        // Convert LocalDate to LocalDateTime
        LocalDateTime dateTime = date.atStartOfDay();
        System.out.println("LocalDateTime: " + dateTime);

        // Convert LocalDateTime to ZonedDateTime
        ZonedDateTime zonedDateTime = dateTime.atZone(ZoneId.systemDefault());
        System.out.println("ZonedDateTime: " + zonedDateTime);
    }
}

Output:

LocalDate: 2023-07-09
LocalDateTime: 2023-07-09T00:00
ZonedDateTime: 2023-07-09T00:00+08:00[Asia/Makassar]

In this example, we’re creating a LocalDate for July 9, 2023. Then we’re converting it to a LocalDateTime, and then to a ZonedDateTime. The atStartOfDay() method returns a LocalDateTime set to the start of the day (00:00) on the date of this LocalDate. The atZone() method then takes the ZoneId and returns a ZonedDateTime representing the start of the day in that timezone.

The ZoneId.systemDefault() returns the system default time zone. If you want to convert it to a specific time zone, you can specify the timezone as a string, like this: ZoneId.of("America/New_York").

How do I convert datetime between time zones?

By Wayan in Java 8, Java Date Time API 0 Comment

The ZonedDateTime class is part of the Java Date-Time Package (java.time.*), released in Java 8 to address the shortcomings of the old date-time classes such as java.util.Date, java.util.Calendar, and java.util.SimpleDateFormat.

Some of the key features are:

  • It represents a date-time with a timezone in the ISO-8601 calendar system, such as ‘2007-12-03T10:15:30+01:00 Europe/Paris’.
  • It provides a lot of methods to play with year, month, day, hour, minute, second and nanosecond fields of the datetime.
  • It’s an immutable class, which is good for multithreaded environments.
  • It provides a fluent interface, which allows method calls to be chained.

Using Java java.time package (which is part of Java 8 and later), you can convert dates between time zones like this:

package org.kodejava.datetime;

import java.time.*;

public class ZonedDateTimeExample {
    public static void main(String[] args) {

        // Create a ZonedDateTime instance for the current date/time
        // in the current timezone
        ZonedDateTime now = ZonedDateTime.now();

        // Create a ZonedDateTime instance for the current date/time
        // in a different timezone
        ZonedDateTime nowInJakarta = now.withZoneSameInstant(ZoneId.of("Asia/Jakarta"));

        // Print the current date/time in the current timezone
        System.out.println("Current date/time: " + now);

        // Print the current date/time in the different timezone
        System.out.println("Current date/time in Jakarta: " + nowInJakarta);
    }
}

Output:

Current date/time: 2024-01-20T21:33:31.236022700+08:00[Asia/Makassar]
Current date/time in Jakarta: 2024-01-20T20:33:31.236022700+07:00[Asia/Jakarta]

The withZoneSameInstant method is used to adjust the date and time based on the timezone. It can be used to convert a datetime value to the datetime in another timezone.

This program will create a ZonedDateTime object representing the current date and time, and then create another ZonedDateTime object that represents the current date and time in Jakarta. Finally, it will print both dates to the console.

How do I use java.time.ZoneId class?

By Wayan in Java 8, Java Date Time API 0 Comment

java.time.ZoneId is a class in Java’s Date-Time API used to represent a time zone identifier. This identifier is used to get a ZoneRules, which then can be used to convert between an Instant and a LocalDateTime.

Here is how you can use the ZoneId class in a simple way:

package org.kodejava.datetime;

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

public class ZoneIdExample {
    public static void main(String[] args) {
        // Get the system default ZoneId
        ZoneId defaultZoneId = ZoneId.systemDefault();
        System.out.println("System Default TimeZone : " + defaultZoneId);

        // Get ZoneId instance using the specified zone ID as a string
        ZoneId londonZoneId = ZoneId.of("Europe/London");
        System.out.println("London ZoneId : " + londonZoneId);

        // Get ZonedDateTime using ZoneId
        ZonedDateTime zonedDateTimeInLondon = ZonedDateTime.now(londonZoneId);
        System.out.println("Current date and time in London: " + zonedDateTimeInLondon);
    }
}

Output:

System Default TimeZone : Asia/Makassar
London ZoneId : Europe/London
Current date and time in London: 2024-01-19T06:43:23.076855Z[Europe/London]

In the above code:

  • ZoneId.systemDefault() is used to get the system default ZoneId.
  • ZoneId.of(String zoneId) is used to get a ZoneId instance using the specified zone ID as a string. You can get all available zone IDs by calling ZoneId.getAvailableZoneIds().
  • ZonedDateTime.now(ZoneId zoneId) is used to get the current date and time in the specified time zone.

Please note that the ZoneId is immutable and thread-safe, it ensures the class can be used safely in multithreaded systems.