How to change miillisecond to Date Object in yyyy-MM-dd HH:mm:ss format

Question

How to change milliseconds to Date object in yyyy-MM-dd HH:mm:ss format like 2017-04-12 23:14:52?

Answer 1

You cannot do that. For a couple of reasons.

TL;DR: Don’t use Date, use Instant. Neither of these can have a format in them. Formatting into a string is dependent on time zone, so you need to choose a time zone.

First, I understand from the discussion that you are asking for a java.util.Date object having the format yyyy-MM-dd HH:mm:ss. A Date object does not have and cannot have a format in it. The thing you should try to understand here is the difference between data itself and presentation of data to a user. An int may hold the value 25389, but it doesn’t hold it in the format 25389 (in fact the internal representation is quite different from 25389). The same int may be presented to a user as 25389, 000025389, 25,389 or +25389, just to mention a few out of many possibilities. The formatting happens outside the int while the int stays just the same.

Similarly, a Date object holds a point in time. The same date may be formatted into for example 2017-04-12 23:14:52 or April 12, 2017 11:14:52 PM. It may even be formatted for different time zones, which would be a good idea if the system has users in different time zones. Alternatively we may show the user a calendar leaf and/or a clock showing the time. Again, formatting happens outside of the Date while the Date stays just the same.

Elaborating on the time zone issue, the same point in time represented by the same millisecond value could be formatted to 2017-04-12 17:44:52 in UTC, 2017-04-12 19:44:52 in my time zone, 2017-04-12 23:14:52 in Asia/Kolkata time zone or even 2017-04-13 05:44:52 in Pacific/Auckland time zone. Note that in the last case not even the date is the same. So there is not just one way to change your milliseconds into the format you asked for. We need to know which time zone you want it for before we can help you.

So what I believe you need is not one thing, but two

1. A way to store your point in time in your program.
2. A way to format your point in time into a string in yyyy-MM-dd HH:mm:ss format for a user in some time zone.

For storing your point in time, use either of

• A long for the milliseconds value you already have
• A java.time.Instant object.

Why didn’t I mention java.util.Date? Because this class is long outdated. Its design turned out to be troublesome very quickly. They tried to repair it by deprecating most of the methods and introducing java.util.Calendar, but that didn’t work very well either. Finally, drawing on the experiences from a library known as Joda-Time they introduced the java.time classes in Java 8 in 2014. That’s three years ago as of writing, and counting. So IMHO we should by now have thrown Date and friends overboard and started using the newer classes. So prefer Instant over Date.

Changing your milliseconds to an Instant is straightforward:

    long milliseconds = 1492019092000L;
    Instant pointInTime = Instant.ofEpochMilli(milliseconds);

For formatting your instant into a string for the user, as I said, we require a time zone. Then do

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm:ss");
    String formattedDateTimeString = pointInTime.atZone(ZoneId.of("Asia/Kolkata"))
            .format(formatter);

So you need to fill in the desired time zone where I put ZoneId.of("Asia/Kolkata"). If you want to use the JVM’s current time zone setting, just fill in ZoneId.systemDefault(). Beware, though, that the time zone setting may be changed, even by an unrelated program running in the same JVM, so relying on this may be fragile.

The result of the above code snippet is a string like

2017-04-12 23:14:52

PS If after reading the above you really insist, here’s how to get a java.util.Date from the above:

    Date myOutdatedDateInstance = Date.from(pointInTime);

(and excuse me for repeating, it still doesn’t have the desired format, that is not possible).

Answer 2

You can try this sample code.

public class MillDateConverter {

    public static String dFormat = "yyy-MM-dd HH:mm:ss";
    private static SimpleDateFormat simpleDateFormat = new SimpleDateFormat(dFormat);


    public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance();
        long milliSec=Long.parseLong("1086073200000");
        System.out.println(milliSec);
        calendar.setTimeInMillis(milliSec);
        System.out.println(simpleDateFormat.format(calendar.getTime()));

    }

}