How to Convert an Instant to LocalDateTime or LocalDate or LocalTime in Java

1. What is Instant in Java?

In Java, Instant is a class in the Java Standard Library (java.time package) that represents a specific point in time without any timezone associated with it, i.e., UTC. An Instant is an immutable representation of a point in time, with a resolution of nanoseconds. It is used to represent timestamps, elapsed time, and other time-related values.

Instant can be created from epoch time, which is the number of seconds that have elapsed since January 1, 1970, at 00:00:00 UTC, or from other date and time-related values, such as LocalDateTime or ZonedDateTime.

An Instant in Java does not have a time zone associated with it. An Instant represents a single point in time, independent of any particular time zone. The value of an Instant is the same regardless of where in the world it is being used, and it does not change based on daylight saving time or other time zone changes.

2. What is LocalDateTime, LocalDate, LocalTime?

LocalDateTime, LocalDate and LocalTime are classes in the Java Standard Library (java.time package) that represent date and time information in a more human-readable format.

LocalDateTime represents a date and time without a time zone, such as 2022-01-20 12:30:15.

LocalDate represents a date without a time or time zone, such as 2022-01-20.

LocalTime represents a time without a date or time zone, such as 12:30:15.

These classes are used when you don't need to track time zones and just need to represent date and time values in a more readable format. They are also used when you need to perform operations on date and time values that don't require knowledge of a specific time zone.

LocalDateTime, LocalDate and LocalTime still provide methods to obtain the current date and time in the default time zone (local time zone where JVM is running) without storing time zone details.

LocalDateTime, LocalDate, LocalTime are not the same across the world. LocalDateTime represents a date and time in the context of a specific time zone. Different time zones have different offsets from Coordinated Universal Time (UTC), so the same LocalDateTime in one time zone will have a different equivalent in another time zone.

Now, let's look at how to convert Instant to LocalDateTime or LocalDate, or LocalTime.

3. Convert from Instant to LocalDateTime/LocalDate/LocalTime

There are two ways to convert from Instant:

3.1. Using atZone() and specifying a ZoneId

The Instant class provides a method atZone which returns ZonedDateTime at the specified time zone. Using this ZonedDateTime, we can convert to LocalDateTime and others.

Instant instant = Instant.now();

LocalDateTime localDateTime = instant.atZone(ZoneId.systemDefault()).toLocalDateTime();

LocalDate localDate = instant.atZone(ZoneId.systemDefault()).toLocalDate();

LocalTime localTime = instant.atZone(ZoneId.systemDefault()).toLocalTime();

3.2. Using ofInstant() of LocalDateTime/LocalDate/LocalTime

All these three classes provide the method ofInstant which accepts Instant and zone ID and converts it to an object of the respective class:

Instant instant = Instant.now();

LocalDateTime.ofInstant(instant, ZoneId.systemDefault())

LocalDate.ofInstant(instant, ZoneId.systemDefault())

LocalTime.ofInstant(instant, ZoneId.systemDefault())

Even though LocalDateTime/LocalDate/LocalTime don't store the time zone information, they always represent date & time in the context of a specific time zone, be it either the system default time zone or any specific time zone across the world. So we need to pass Zone Id along with instant.

4. Conclusion

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