Java 8 examples to show you how to convert from Instant to LocalDateTime
1. Instant -> LocalDateTime
The java.time.LocalDateTime has no concept of time zone, just provide a zero offset UTC+0.
InstantExample1.java
package com.mkyong.date;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
public class InstantExample1 {
    public static void main(String[] argv) {
        // Parse a ISO 8601 Date directly
        //Instant instant = Instant.parse("2016-08-18T06:17:10.225Z");
        Instant instant = Instant.now();
        System.out.println("Instant : " + instant);
        //Convert instant to LocalDateTime, no timezone, add a zero offset / UTC+0
        LocalDateTime ldt = LocalDateTime.ofInstant(instant, ZoneOffset.UTC);
        System.out.println("LocalDateTime : " + ldt);
    }
}
Output
Instant : 2016-08-18T06:17:10.225Z
LocalDateTime : 2016-08-18T06:17:10.225
2. LocalDateTime -> Instant
InstantExample2.java
package com.mkyong.date;
import java.time.*;
public class InstantExample2 {
    public static void main(String[] argv) {
        // Hard code a date time
        LocalDateTime dateTime = LocalDateTime.of(2016, Month.AUGUST, 18, 6, 17, 10);
        System.out.println("LocalDateTime : " + dateTime);
        // Convert LocalDateTime to Instant, UTC+0
        Instant instant = dateTime.toInstant(ZoneOffset.UTC);
        System.out.println("Instant : " + instant);
    }
}
Output
Instant : 2016-08-18T06:17:10.225Z
LocalDateTime : 2016-08-18T06:17:10.225
References
- Wikipedia – ISO 8601 date format
- Instant JavaDoc
- LocaldateTime JavaDoc