Java Instant
last modified July 10, 2024
In this article we show how to use Instant to define moments in time in Java.
Instant represents a specific moment in time on the timeline. It's
akin to a single point on a never-ending line. Unlike other date and time
classes, Instant doesn't inherently include time zone information.
Instead, it measures time as the number of seconds and nanoseconds elapsed since
a specific point in time, known as the epoch.
The epoch is January 1st, 1970, at 00:00:00 Coordinated Universal Time (UTC). Positive Instant values represent times after the epoch, while negative values indicate times before.
Common use cases for Instant include:
- Recording timestamps for events within an application.
- Storing timestamps in databases where UTC is the preferred time format.
- Performing calculations based on the number of seconds or nanoseconds elapsed since a specific point in time.
Current timestamp
We get the current timestamp with Instant.now.
import java.time.Instant;
void main() {
var timestamp = Instant.now();
System.out.println("The current timestamp: " + timestamp);
}
The example prints the current timestamp.
$ java Main.java The current timestamp: 2024-07-10T14:37:39.890616200Z
Unix time
Unix time (also known as POSIX time or epoch time) is a system for describing a point in time, defined as the number of seconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970, minus the number of leap seconds that have taken place since then.
import java.time.Instant;
void main() {
Instant now = Instant.now();
long unixTime = now.toEpochMilli();
System.out.println(unixTime);
}
We compute the current Unix time in milliseconds.
$ java Main.java 1720623471356
The plus/minus methods
The plus/minus methods can be used to add datetime
units to the instant.
import java.time.Instant;
import java.time.temporal.ChronoUnit;
void main() {
var timestamp = Instant.now();
var res = timestamp.plus(5, ChronoUnit.DAYS);
System.out.println(res);
res = timestamp.plusSeconds(78566);
System.out.println(res);
res = timestamp.minus(57, ChronoUnit.HOURS);
System.out.println(res);
}
The example gets the current instant and adds 5 days, 78566 seconds, and subtracts 57 hours.
$ java Main.java 2024-07-15T14:42:46.830593700Z 2024-07-11T12:32:12.830593700Z 2024-07-08T05:42:46.830593700Z
Formatting Instant
We use DateTimeFormatter to format instants.
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
void main() {
var timestamp = Instant.now();
System.out.println(timestamp);
DateTimeFormatter df1 = DateTimeFormatter.ISO_DATE_TIME.withZone(ZoneId.of("UTC"));
System.out.println(df1.format(timestamp));
DateTimeFormatter df2 = DateTimeFormatter.RFC_1123_DATE_TIME.withZone(ZoneId.of("UTC"));;
System.out.println(df2.format(timestamp));
}
Since Instant does not include date or time components, only
represents a point in time, we add the zone with
withZone(ZoneId.of("UTC")).
$ java Main.java 2024-07-10T14:51:09.957078500Z 2024-07-10T14:51:09.9570785Z[UTC] Wed, 10 Jul 2024 14:51:09 GMT
Converting to LocalDateTime
In the following example we show how to convert an Instnt to
LocalDateTime.
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
void main() {
Instant now = Instant.now();
LocalDateTime localDateTimePST = LocalDateTime.ofInstant(now, ZoneId.of("Europe/Bratislava"));
System.out.println("Current time in Bratislava: " + localDateTimePST);
}
In the example we convert the Instant to LocalDateTime
for a specific time zone (Europe/Bratislava).
$ java Main.java Current time in Bratislava: 2024-07-10T16:54:46.319805200
Source
Java Instant - language reference
In this article we have used Java Instant to define moments in time.
Author
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