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September 2, 2009

Groovy Goodness: Date and Time Durations and the TimeCategory

Groovy has some elegant ways to work with date and time values. One of them is the support of durations. We can define a duration to denote a certain time amount, like 7 days, 2 hours and 50 minutes. We can use these durations to add or subtract them from date and time objects.

The TimeCategory provides an even Groovier way to work with durations. We can use constructs like 7.days + 12.minutes to create a duration. When we read this code it is just like reading English text. Here is some sample code:

import groovy.time.*
import org.codehaus.groovy.runtime.TimeCategory

// Define period of 2 years, 3 months, 15 days, 0 hours, 23 minutes, 2 seconds and 0 milliseconds.
def period = new DatumDependentDuration(2, 3, 15, 0, 23, 2, 0)
assert '2 years, 3 months, 15 days, 23 minutes, 2.000 seconds' == period.toString()
def year2000 = new Date(100, 0, 0)  // Jan 1, 2000
assert 'Mon Apr 15 00:23:02 UTC 2002' == (period + year2000).toString()

// Define time period of 5 hours, 54 minutes and 30 milliseconds.
def time = new TimeDuration(5, 54, 0, 30)
assert '5 hours, 54 minutes, 0.030 seconds' == time.toString()

use (TimeCategory) {
    assert period.toString() == (2.years + 3.months + 15.days + 0.hour + 23.minutes + 2.seconds).toString()
    assert time.toString() == (5.hours + 54.minutes + 30.milliseconds).toString()

    // We can use period.from.now syntax.    
    def d1 = 1.week - 1.day
    def d2 = new Date() + 6.days
    assert d2.format('yyyy-MM-dd') == d1.from.now.toString()
    
    // We can use period.ago syntax.
    def d3 = 3.days.ago
    def d4 = new Date() - 3
    assert d4.format('yyyy-MM-dd') == d3.toString()
}