How to create a Java or Scala date from a Long value

By Alvin Alexander. Last updated: May 18, 2022

Scala/Java date FAQ: How do I create a Scala Date from a Long value? When I give the Java Date class constructor a Long value it returns a date from 1970.

Solution

You need to multiply the Long value by 1000, and also make sure you pass a Long value into the Date constructor. The Scala REPL shows how this works:

scala> import java.util._
import java.util._

# WRONG: 1970?
scala> val d = new Date(1513714678)
d: java.util.Date = Sun Jan 18 05:28:34 MST 1970

# WRONG: multiply by 1000 and it’s still 1970?
scala> val d = new Date(1513714678 * 1000)
d: java.util.Date = Thu Jan 22 12:56:29 MST 1970

# SOLUTION: multiply by 1000 and make sure you pass in a Long
scala> val d = new Date(1513714678 * 1000L)
d: java.util.Date = Tue Dec 19 13:17:58 MST 2017

The reason you need to do these two things are:

The Java Date constructor expects the time to be in milliseconds, not seconds
The Date constructor expects a Long value

In the second case I haven’t looked into the Date source code to see why an integer causes such a problem with the Date constructor. All I can say at this time is that passing an Integer/Int value into the Date constructor clearly causes a problem.

On a personal note, I ran into this problem when working with a MySQL database for a Drupal website. Drupal is written in PHP, and PHP dates are stored as a Long value, as shown in my 1513714678 example.

Example Long-to-Date functions

While I’m in the neighborhood, here are two “Long to Date” functions that I created in that Scala/Drupal app:

import java.text.SimpleDateFormat
import java.util.Date

object DateUtils {

    def formatDateForBlogPages(date: Long): String = {
        val d = new Date(date * 1000L)
        new SimpleDateFormat("LLLL d, yyyy").format(d)
    }

    def formatDateForSitemap(date: Long): String = {
        val d = new Date(date * 1000L)
        new SimpleDateFormat("yyyy-MM-d").format(d)
    }

}

In summary, if you wanted to see how to create a Scala Date from a Long value, I hope this example is helpful.