DateDiffTest.java

package com.vsct;

import org.junit.Test;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.TimeUnit;

import static org.junit.Assert.assertEquals;

public class DateDiffTest {

    @Test
    public void test_DateDiff() throws Exception {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS ZZZ");

        Date date1 = dateFormat.parse("2007-03-24T10:00:00.000 UTC");
        Date date2 = dateFormat.parse("2007-03-25T12:01:01.001 UTC");

        assertEquals("1 days 02h 01m 01s", daysDuration(date2.getTime() - date1.getTime()));
        assertEquals("26h 01m 01s", hoursDuration(date2.getTime() - date1.getTime()));

    }

    /**
     * Formats Date/Time difference to String in hours
     */
    public static String hoursDuration(long durationMillis) {
        DateDiff dateDiff = new DateDiff(durationMillis, TimeUnit.HOURS);

        return String.format("%02dh %02dm %02ds",
                dateDiff.get(TimeUnit.HOURS),
                dateDiff.get(TimeUnit.MINUTES),
                dateDiff.get(TimeUnit.SECONDS));
    }

    /**
     * Formats Date/Time difference to String in days
     */
    public static String daysDuration(long durationMillis) {
        DateDiff dateDiff = new DateDiff(durationMillis, TimeUnit.DAYS);

        long days = dateDiff.get(TimeUnit.DAYS);
        return String.format((days>0 ? "%d days " : "") + "%02dh %02dm %02ds",
                dateDiff.get(TimeUnit.DAYS),
                dateDiff.get(TimeUnit.HOURS),
                dateDiff.get(TimeUnit.MINUTES),
                dateDiff.get(TimeUnit.SECONDS));
    }

    /**
     * Calculates Time units for a Date Difference
     */
    private static class DateDiff {
        private static final TimeUnit[] TIME_UNITS = TimeUnit.values();
        long[] mTimeUnitResult = new long[TIME_UNITS.length];

        public DateDiff(long millis) {
            this(millis, TimeUnit.DAYS);
        }

        public DateDiff(long millis, TimeUnit baseUnit) {
            for (int r = baseUnit.ordinal(); r >= 0; r--) {
                TimeUnit unit = TIME_UNITS[r];
                mTimeUnitResult[r] = unit.convert(millis, TimeUnit.MILLISECONDS);
                millis -= unit.toMillis(mTimeUnitResult[r]);
            }
        }

        public long get(TimeUnit unit) {
            return mTimeUnitResult[unit.ordinal()];
        }
   }
}