Java 9 – How to convert java.util.Date to LocalTime using ofInstant() method ?

August 26, 2022 SJ Java 8, Java 8 Date/Time 0

In this article, we will learn how to convert Date to LocalTime using newly introduced method in Java 1.9 version

Date class in Java 1.8 version :

  • There are 2 new methods introduced in Java 1.8 version for Date class, those are
    1. from(Instant) – This static method obtains an instance of Date from an Instant object
    2. toInstant() – This method converts invoking Date object to an Instant
  • Note: Many legacy methods of Date class are deprecated

1. Convert Date to LocalTime in Java 1.9 version :

  • First, convert Date to an Instant using toInstant() method of Date class
  • In Java 1.9 version a new method LocalTime.ofInstant() introduced for conversion from an Instant to LocalTime,
    • LocalTime.ofInstant​(Instant, ZoneId) – gets an instance of LocalTime from an Instant and zone ID passed

ConvertJavaUtilDateToLocalTime.java

package in.bench.resources.java9.conversion;

import java.time.Instant;
import java.time.LocalTime;
import java.time.ZoneId;
import java.util.Date;

public class ConvertJavaUtilDateToLocalTime {

	public static void main(String[] args) {

		// 1. get current date/time using java.util.Date
		Date date = new Date();
		System.out.println("Current Date/time is :- \n" 
				+ date);


		// 2. get default time zone
		ZoneId zoneId = ZoneId.systemDefault();
		System.out.println("\nDefault time-zone is :- \n" 
				+ zoneId);


		// 3. First, convert Date to Instant
		Instant instant = date.toInstant();
		System.out.println("\nInstant is :- \n" 
				+ instant);


		// 4. Second, Instant -> LocalTime
		LocalTime localTime = LocalTime
				.ofInstant(instant, zoneId);
		System.out.print("\nLocalTime is :- \n" 
				+ localTime);
	}
}

Output:

Current Date/time is :- 
Thu Aug 25 09:38:34 IST 2022

Default time-zone is :- 
Asia/Calcutta

Instant is :- 
2022-08-25T04:08:34.908Z

LocalTime is :- 
09:38:34.908

2. Convert LocalTime to Date :

  • LocalTime consist of only Time information whereas java.util.Date requires Date, Time and Zone information
    • java.util.Date = Date + LocalTime + Zone information
    • For LocalTime to java.util.Date conversion, Time-Zone and Date information is required
  • Date.from() method accepts Instant as input-argument
    1. First, convert LocalTime to LocalDateTime by adding/combining LocalDate using atDate() method of LocalTime
    2. Second, convert LocalDateTime to ZonedDateTime by adding/combining Zone information using atZone() method of LocalDateTime
    3. Third, convert ZonedDateTime to Instant using toInstant() method of ZonedDateTime which returns an Instant
    4. Finally, pass above converted Instant to Date.from() method which will return java.util.Date
  • Converted java.util.Date will have,
    1. Date part added as today’s date
    2. Adding System default Zone information
    3. Time part remain same as that of LocalTime
  • In short, LocalTime -> LocalDateTime -> ZonedDateTime -> Instant -> java.util.Date
  • Lets see an example for conversion of LocalTime to java.util.Date in the below illustration

ConvertLocalTimeToJavaUtilDate.java

package in.bench.resources.java9.conversion;

import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalTime;
import java.time.Month;
import java.time.ZoneId;
import java.util.Date;

public class ConvertLocalTimeToJavaUtilDate {

	public static void main(String[] args) {

		// 1. get current system time
		LocalTime localTime = LocalTime.now();
		System.out.println("Current system time is :- \n" 
				+ localTime);


		// 2. get current system date
		LocalDate localDate = LocalDate.of(2022, Month.AUGUST, 26);
		System.out.println("\nCurrent system date is :- \n" 
				+ localDate);


		// 3. get default time zone
		ZoneId zoneId = ZoneId.systemDefault();
		System.out.println("\nDefault time-zone is :- \n" 
				+ zoneId);


		// 4. convert LocalTime -> LocalDateTime -> ZonedDateTime -> Instant
		Instant instant = localTime // LocalTime
				.atDate(localDate) // LocalDateTime
				.atZone(zoneId) // ZonedDateTime
				.toInstant(); // Instant
		System.out.println("\nCurrent Instant at UTC/GMT is :- \n" 
				+ instant);


		// 5. finally convert to Date
		Date date = Date.from(instant);
		System.out.print("\nConverted Date/time is :- \n" + date);
	}
}

Output:

Current system time is :- 
09:55:16.088092700

Current system date is :- 
2022-08-26

Default time-zone is :- 
Asia/Calcutta

Current Instant at UTC/GMT is :- 
2022-08-26T04:25:16.088092700Z

Converted Date/time is :- 
Fri Aug 26 09:55:16 IST 2022

Related Articles:

References:

Happy Coding !!
Happy Learning !!

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