Convert between Java LocalDateTime and Epoch
August 30, 2019
LocalDateTime and epoch time. An epoch is an instant in time used as an origin of particular calendar era. Epoch is a reference point from which a time is measured. The epoch reference point for LocalDateTime is 1970-01-01T00:00:00Z in UTC. When we convert a local date-time such as 2019-11-15T13:15:30 into epoch seconds, then the result will be time gap in seconds from 1970-01-01T00:00:00Z to 2019-11-15T13:15:30. In the same way, when we convert epoch seconds such as 1567109422 to LocalDateTime then the resulting LocalDateTime will be obtained by adding 1567109422 seconds to 1970-01-01T00:00:00Z.
1. Find the code snippet to convert
LocalDateTime to epoch seconds using LocalDateTime.toEpochSecond().
long timeInSeconds = localDateTime.toEpochSecond(ZoneOffset.UTC);
LocalDateTime using LocalDateTime.ofEpochSecond().
LocalDateTime localDateTime = LocalDateTime.ofEpochSecond(timeInSeconds, 0, ZoneOffset.UTC);
LocalDateTime and epoch time in detail.
Contents
1. LocalDateTime to Epoch
To convertLocalDateTime to epoch seconds or milliseconds is the time calculation starting from 1970-01-01T00:00:00Z up to given local date-time. Find the code.
LocalDateTimeToEpoch.java
package com.concretepage;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
public class LocalDateTimeToEpoch {
public static void main(String[] args) {
//1970-01-01T00:00:00Z
LocalDateTime localDateTime = LocalDateTime.parse("2019-11-15T13:15:30");
//LocalDateTime to epoch seconds
long timeInSeconds = localDateTime.toEpochSecond(ZoneOffset.UTC);
System.out.println(timeInSeconds);
//LocalDateTime to epoch milliseconds
Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant();
long timeInMillis = instant.toEpochMilli();
System.out.println(timeInMillis);
}
}
1573823730 1573803930000
1.1 LocalDateTime to Epoch Seconds
LocalDateTime provides toEpochSecond() method to convert local date-time into epoch seconds. Find the Java doc.
long toEpochSecond(ZoneOffset offset)
toEpochSecond() combines this local date-time and the specified offset to calculate the epoch-second value. toEpochSecond() calculates number of seconds starting from 1970-01-01T00:00:00Z up to given local date-time.
long timeInSeconds = localDateTime.toEpochSecond(ZoneOffset.UTC);
1.2 LocalDateTime to Epoch Milliseconds
To convertLocalDateTime to epoch milliseconds, we can use Instant.toEpochMilli() that converts this instant to the number of milliseconds from the epoch of 1970-01-01T00:00:00Z. To get epoch milliseconds, first we will convert LocalDateTime to Instant and then will use its toEpochMilli() method.
Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant(); long timeInMillis = instant.toEpochMilli();
2. Epoch to LocalDateTime
The given epoch seconds or milliseconds are converted intoLocalDateTime by adding the given time to 1970-01-01T00:00:00Z. Find the code.
EpochToLocalDateTime.java
package com.concretepage;
import java.sql.Timestamp;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
public class EpochToLocalDateTime {
public static void main(String[] args) {
//Epoch point of time is 1970-01-01T00:00:00Z
long timeInSeconds = 1567109422L;
//Using LocalDateTime.ofEpochSecond
LocalDateTime localDateTime = LocalDateTime.ofEpochSecond(timeInSeconds, 0, ZoneOffset.UTC);
System.out.println(localDateTime);
//Using Instant
localDateTime = LocalDateTime.ofInstant(Instant.ofEpochSecond(timeInSeconds), ZoneId.systemDefault());
System.out.println(localDateTime);
localDateTime = LocalDateTime.ofInstant(Instant.ofEpochSecond(timeInSeconds, 0), ZoneId.systemDefault());
System.out.println(localDateTime);
long timeInMillis = 1567109422123L;
localDateTime = LocalDateTime.ofInstant(Instant.ofEpochMilli(timeInMillis), ZoneId.systemDefault());
System.out.println(localDateTime);
//Using Timestamp
localDateTime = new Timestamp(timeInMillis).toLocalDateTime();
System.out.println(localDateTime);
}
}
2019-08-29T20:10:22 2019-08-30T01:40:22 2019-08-30T01:40:22 2019-08-30T01:40:22.123 2019-08-30T01:40:22.123
2.1 Epoch to LocalDateTime using LocalDateTime.ofEpochSecond()
LocalDateTime.ofEpochSecond() obtains an instance of LocalDateTime using seconds from the epoch of 1970-01-01T00:00:00Z. Find the Java doc.
static LocalDateTime ofEpochSecond(long epochSecond, int nanoOfSecond, ZoneOffset offset)
LocalDateTime localDateTime = LocalDateTime.ofEpochSecond(timeInSeconds, 0, ZoneOffset.UTC);
2.2 Epoch to LocalDateTime using Instant
Instant provides following methods to handle epoch time.
1. This method obtains an instance of
Instant using seconds from the epoch of 1970-01-01T00:00:00Z.
static Instant ofEpochSecond(long epochSecond)
localDateTime = LocalDateTime.ofInstant(Instant.ofEpochSecond(timeInSeconds), ZoneId.systemDefault());
Instant using seconds from the epoch of 1970-01-01T00:00:00Z and nanosecond fraction of second.
static Instant ofEpochSecond(long epochSecond, long nanoAdjustment)
localDateTime = LocalDateTime.ofInstant(Instant.ofEpochSecond(timeInSeconds, 0), ZoneId.systemDefault());
Instant using milliseconds from the epoch of 1970-01-01T00:00:00Z.
static Instant ofEpochMilli(long epochMilli)
localDateTime = LocalDateTime.ofInstant(Instant.ofEpochMilli(timeInMillis), ZoneId.systemDefault());
2.3 Epoch to LocalDateTime using Timestamp
Find thejava.sql.Timestamp constructor.
public Timestamp(long time)
Timestamp object using milliseconds time value since 1970-01-01T00:00:00Z.
Find the code snippet.
localDateTime = new Timestamp(timeInMillis).toLocalDateTime();
References
Class LocalDateTimeClass Instant
