date - How do I ignore weekends using the Java calendar?

Question

I'm trying to get the number of minutes between two particular time instances by ignoring weekends. This is what I've done.

public static final List<Integer> NON_WORKING_DAYS;
static {
    List<Integer> nonWorkingDays = new ArrayList<Integer>();
    nonWorkingDays.add(Calendar.SATURDAY);
    nonWorkingDays.add(Calendar.SUNDAY);
    NON_WORKING_DAYS = Collections.unmodifiableList(nonWorkingDays);
}

public static int getMinsBetween(Date d1, Date d2, boolean onlyBusinessDays)
{
    int minsBetween = (int)((d2.getTime() - d1.getTime()) / (1000 * 60));
    int minsToSubtract = 0;
    if(onlyBusinessDays){
        Calendar dateToCheck = Calendar.getInstance();
        dateToCheck.setTime(d1);
        Calendar dateToCompare = Calendar.getInstance();
        dateToCompare.setTime(d2);


        //moving the first day of the week to Tues so that a Sat, sun and mon fall in the same week, easy to adjust dates
        dateToCheck.setFirstDayOfWeek(Calendar.TUESDAY);
        dateToCompare.setFirstDayOfWeek(Calendar.TUESDAY);

        //moving the dates out of weekends
        if(!isBusinessDay(dateToCheck, NON_WORKING_DAYS)){
            dateToCheck.set(Calendar.DAY_OF_WEEK, Calendar.SATURDAY);
            dateToCheck.set(Calendar.HOUR, 0);
            dateToCheck.set(Calendar.MINUTE, 0);
            dateToCheck.set(Calendar.SECOND, 0);
            dateToCheck.set(Calendar.MILLISECOND, 0);
        }

        if(!isBusinessDay(dateToCompare, NON_WORKING_DAYS)){
            dateToCompare.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
            dateToCompare.set(Calendar.HOUR, 0);
            dateToCompare.set(Calendar.MINUTE, 0);
            dateToCompare.set(Calendar.SECOND, 0);
            dateToCompare.set(Calendar.MILLISECOND, 0);
        }

        for(; dateToCheck.getTimeInMillis() < dateToCompare.getTimeInMillis() ; dateToCheck.add(Calendar.DAY_OF_MONTH, 1)){
            if(isBusinessDay(dateToCheck, NON_WORKING_DAYS)){
                minsToSubtract = minsToSubtract + 1440;
            }
        }
    minsBetween = minsBetween - minsToSubtract; 
    }
    return minsBetween;
}


private static boolean isBusinessDay(Calendar dateToCheck, List<Integer> daysToExclude){
    for(Integer dayToExclude : daysToExclude){
        if(dayToExclude != null && dayToExclude == dateToCheck.get(Calendar.DAY_OF_WEEK)) {
            return true; 
        }
        else continue;
    }
    return false;
}

Can someone tell me if my logic is correct and if not how to do this? I'm not too sure how this code would behave when the month changes over the weekend.

Expected output for some test cases:

1. Friday 6 pm, Monday 6 am - should return 12 hours
2. Saturday 12 pm, Sunday 12 pm - should return 0 hours
3. Saturday 12 pm, Monday 6 am - should return 6 hours

Answer 1

I would highly recommend using Joda-Time for anything concerning date manipulations in Java, because it comes with a lot of helpful functions to make the code less complicated.

This code uses JodaTime:

public static final List<Integer> NON_WORKING_DAYS;
static {
    List<Integer> nonWorkingDays = new ArrayList<Integer>();
    nonWorkingDays.add(DateTimeConstants.SATURDAY);
    nonWorkingDays.add(DateTimeConstants.SUNDAY);
    NON_WORKING_DAYS = Collections.unmodifiableList(nonWorkingDays);
}

public static Minutes getMinsBetween(DateTime d1, DateTime d2,
        boolean onlyBusinessDays) {

    BaseDateTime startDate = onlyBusinessDays && !isBusinessDay(d1) ?
                new DateMidnight(d1) : d1;
    BaseDateTime endDate = onlyBusinessDays && !isBusinessDay(d2) ?
                new DateMidnight(d2) : d2;

    Minutes minutes = Minutes.minutesBetween(startDate, endDate);

    if (onlyBusinessDays) {
        DateTime d = new DateTime(startDate);

        while (d.isBefore(endDate)) {
            if (!isBusinessDay(d)) {
                Duration dayDuration = new Duration(d, d.plusDays(1));
                minutes = minutes.minus(int) dayDuration.getStandardMinutes());
            }
            d = d.plusDays(1);
        }
    }
    return minutes;
}

private static boolean isBusinessDay(DateTime dateToCheck) {
    return !NON_WORKING_DAYS.contains(dateToCheck.dayOfWeek().get());
}

When this code is tested, it gives the following results:

DateTime d1 = new DateTime(2013, 1, 4, 18, 0); // a Friday, 6 pm
DateTime d2 = new DateTime(2013, 1, 7, 6, 0);  // the following Monday, 6 am

Minutes minutes = getMinsBetween(d1, d2, true);
System.out.println(minutes.toStandardHours().getHours()); // outputs "12" (in hours)

d1 = new DateTime(2013, 1, 5, 12, 0); // a Saturday, 12 pm
d2 = new DateTime(2013, 1, 6, 12, 0); // the following Sunday, 12 pm

minutes = getMinsBetween(d1, d2, true);
System.out.println(minutes.toStandardHours().getHours()); // outputs "0" (in hours)

d1 = new DateTime(2013, 1, 5, 12, 0); // a Saturday, 12 pm
d2 = new DateTime(2013, 1, 7, 6, 0);  // the following Monday, 6 am

minutes = getMinsBetween(d1, d2, true);
System.out.println(minutes.toStandardHours().getHours()); // outputs "6" (in hours)

I just tested a case where the month changes over the weekend: From Friday, March 29th (6pm) to Monday, April 1st (6am):

d1 = new DateTime(2013, 3, 29, 18, 0);
d2 = new DateTime(2013, 4, 1, 6, 0);

minutes = getMinsBetween(d1, d2, true);
System.out.println(minutes.toStandardHours().getHours());

The result is 12 hours, so it works for the month change.

---

My first solution wasn't handling daylight saving times correctly. We have to determine the duration of each actual day when subtracting the minutes because days with a change in daylight saving time will not be 24h:

if (!isBusinessDay(d)) {
    Duration dayDuration = new Duration(d, d.plusDays(1));
    minutes = minutes.minus(int) dayDuration.getStandardMinutes());
}