Get the number of days, weeks, and months, since Epoch in Java

Question

I\'m trying to get the number of days, weeks, months since Epoch in Java.

The Java Calendar class offers things like calendar.get(GregorianCalendar.DAY_OF_YEAR), or

Answer 1

I'm kind of surprised that almost all answers are actually calculating days between epoch and now. With java.time.LocalDate it's as simple as:

LocalDate.now().toEpochDay()

Answer 2

Date.getTime() - Returns the number of milliseconds since January 1, 1970, 00:00:00 GMT represented by this Date object.

You can use this and knowledge of how many milliseconds are in the intervals you care about to do the calculations.

Answer 3

I wouldn't expect there to be an elegant way of doing it since it is not a very common requirement. I can't help but wonder why you want to do it...

But anyway, the way I would do it is to subtract the epoch date from the Calendar and then get the fields you want:

Calendar timeSinceEpoch = Calendar.getInstance();
timeSinceEpoch.add(Calendar.YEAR, -1970);

int yearsSinceEpoch = timeSinceEpoch.get(Calendar.YEAR);
int monthsSinceEpoch = timeSinceEpoch.get(Calendar.MONTH) + 12 * yearsSinceEpoch;

Answer 4

Long currentMilli = System.currentTimeMillis();
Long seconds = currentMilli / 1000;
Long minutes = seconds / 60;
Long hours = minutes / 60;
Long days = hours / 24;
System.out.println("Days since epoch : "  + days);

or

System.out.println("Days since epoch : "  + ((int) currentMilli / 86400000));

Answer 5

You can use the Joda Time library to do this pretty easily - I use it for anything time related other than using the standard Java Date and Calendar classes. Take a look at the example below using the library:

MutableDateTime epoch = new MutableDateTime();
epoch.setDate(0); //Set to Epoch time
DateTime now = new DateTime();

Days days = Days.daysBetween(epoch, now);
Weeks weeks = Weeks.weeksBetween(epoch, now);
Months months = Months.monthsBetween(epoch, now);

System.out.println("Days Since Epoch: " + days.getDays());
System.out.println("Weeks Since Epoch: " + weeks.getWeeks());
System.out.println("Months Since Epoch: " + months.getMonths());

When I run this I get the following output:

Days Since Epoch: 15122
Weeks Since Epoch: 2160
Months Since Epoch: 496

Answer 6

java.time

Use the java.time classes built into Java 8 and later.

LocalDate now = LocalDate.now();
LocalDate epoch = LocalDate.ofEpochDay(0);

System.out.println("Days: " + ChronoUnit.DAYS.between(epoch, now));
System.out.println("Weeks: " + ChronoUnit.WEEKS.between(epoch, now));
System.out.println("Months: " + ChronoUnit.MONTHS.between(epoch, now));

Output

Days: 16857
Weeks: 2408
Months: 553