[Java] 日数計算

DayUtil.java

import org.apache.commons.lang.time.DateUtils;
public static long differenceDay(Date date1, Date date2) {
  final long millsecsOfDay = 24 * 60 * 60 * 1000;
  Date day1 = DateUtils.truncate(date1, Calendar.DATE);
  Date day2 = DateUtils.truncate(date2, Calendar.DATE);
  return (day1.getTime() - day2.getTime()) / millsecsOfDay;
}

DayUtilTest.java

private Date date1;

@Before
public void setUp() throws Exception {
  Calendar cal = Calendar.getInstance();
  cal.set(2011, Calendar.AUGUST, 31, 12, 0, 30);
  date1 = cal.getTime();
}

@Test
public void testDifferenceDayLastTime() {
  Calendar cal = Calendar.getInstance();
  cal.set(2011, Calendar.JULY, 31, 23, 59, 59);
  Date date2 = cal.getTime();
  assertEquals(31, differenceDay(date1, date2));
}

@Test
public void testDifferenceDayFirstTime() {
  Calendar cal = Calendar.getInstance();
  cal.set(2011, Calendar.JULY, 31, 0, 0, 0);
  Date date2 = cal.getTime();
  assertEquals(31, differenceDay(date1, date2));
}

@Test
public void testDifferenceDayFirstDayOfThisMonth() {
  Calendar cal = Calendar.getInstance();
  cal.set(2011, Calendar.AUGUST, 1);
  Date date2 = cal.getTime();
  assertEquals(30, differenceDay(date1, date2));
}

@Test
public void testDifferenceDaySameDayOfPrevYear() {
  Calendar cal = Calendar.getInstance();
  cal.set(2010, Calendar.AUGUST, 31);
  Date date2 = cal.getTime();
  assertEquals(365, differenceDay(date1, date2));
}

@Test
public void testDifferenceDayZero() {
  Calendar cal = Calendar.getInstance();
  cal.set(2011, Calendar.AUGUST, 31);
  Date date2 = cal.getTime();
  assertEquals(0, differenceDay(date1, date2));
}

@Test
public void testDifferenceDayMinus() {
  Calendar cal = Calendar.getInstance();
  cal.set(2011, Calendar.SEPTEMBER, 1);
  Date date2 = cal.getTime();
  assertEquals(-1, differenceDay(date1, date2));
}

@Test
public void testDifferenceDayLarge() {
  Calendar cal = Calendar.getInstance();
  cal.set(1970, Calendar.JANUARY, 1);
  Date date2 = cal.getTime();
  assertEquals(15217, differenceDay(date1, date2));
}

@Test
public void testDateUtilsTruncate() {
  Calendar cal = Calendar.getInstance();
  cal.set(2010, Calendar.JULY, 31, 23, 59, 59);
  assertEquals(23, cal.get(Calendar.HOUR_OF_DAY));
  assertEquals(59, cal.get(Calendar.MINUTE));
  assertEquals(59, cal.get(Calendar.SECOND));

  cal.setTime(DateUtils.truncate(cal.getTime(), Calendar.DATE));

  assertEquals(0, cal.get(Calendar.HOUR_OF_DAY));
  assertEquals(0, cal.get(Calendar.MINUTE));
  assertEquals(0, cal.get(Calendar.SECOND));
  assertEquals(2010, cal.get(Calendar.YEAR));
  assertEquals(Calendar.JULY, cal.get(Calendar.MONTH));
  assertEquals(31, cal.get(Calendar.DAY_OF_MONTH));
}