How to find the number of days between two dates in java or groovy?

Question

I have a method which uses following logic to calculate difference between days.

long diff = milliseconds2 - milliseconds1;
long diffDays = diff / (24 * 60 * 60 * 1000);

but I want for ex, 9th feb 2011 to 19th feb 2011 should return me 11 days irrespective of second or milliseconds consideration. How can I achieve this?

Answer 1

It's a well worn line, but for Dates use JodaTime.

Here's how to calculate date intervals using JodaTime.

Days days = Days.daysBetween(new DateTime(millis1), new DateTime(millis2));
int daysBetweenDates = days.getDays();

Answer 2

For the groovy solution you asked for you should consider using this:

use(groovy.time.TimeCategory) {
   def duration = date1 - date2
   println "days: ${duration.days}, Hours: ${duration.hours}"
}

It's very easy to understand and extremely readable. You asked for a example how this can be used in an easy method which calculates the days between two dates. So here is your example.

class Example {

    public static void main(String[] args) {
        def lastWeek = new Date() - 7;
        def today = new Date()

        println daysBetween(lastWeek, today)
    }

    static def daysBetween(def startDate, def endDate) {
        use(groovy.time.TimeCategory) {
            def duration = endDate - startDate
            return duration.days
        }
    }
}

If you run this example it will print you 7. You can also enhance this method by using before() and after() to enable inverted dates.