Groovy Goodness: Loop Through Date and Calendar Ranges

Groovy already adds a lot of extra methods to the Date and Calendar classes. And since Groovy 2.2 we can use the upto() method and loop over a begin date up to another date. We pass a closure that is executed for each day. We can also iterate back using the downto() method.

// We can loop from today
// to nextWeek and invoke a closure for each day.
def today = new Date().clearTime()
def nextWeek = today + 7

today.upto(nextWeek) {
    // Print day of the week.
    println it.format('EEEE')
}

println()

nextweek.downto(today) {
    prinltn it.format('EEEE')
}

When we run the code we get the following output:

Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
Monday
 
Monday
Sunday
Saturday
Friday
Thursday
Wednesday
Tuesday
Monday

In the next sample we use the upto() method on the Calendar class:

// upto() also works on Calendar objects.
def to = Calendar.instance
to.set(year: 2013, month: Calendar.NOVEMBER, date: 18)

def from = Calendar.instance
from.set(year: 2013, month: Calendar.NOVEMBER, date: 13)

from.upto(to) {
    if (it[Calendar.DATE] % 2 == 0) {
        print 'Even'
    } else {
        print 'Odd'
    }
    println ' date'
}

We get the following output:

Odd date
Even date
Odd date
Even date
Odd date
Even date