Difference between two dates, including only business days (i.e. excluding weekends and holidays)

Question

How can I get the number of business days between two java.util.Date, i.e. excluding weekends and holidays? By holidays, I mean legally recognized holidays. It must be depending on the country, because of the holidays that are different from a country to another.

For example, 2012-08-27 - 2012-08-24 should return 1 instead of 3, because of the weekend inbetween.

I already had a look on Jollyday and ObjectLab-Kit, but I can't make them meet my need. I mean, both of them have a lot of interesting methods, but can't find something like getBusinessDaysCount(Date d1, Date d2)...

Answer 1

Here is finally a solution based on the Calendar API:

/**
 * Handles holidays by country.
 */
public enum Holidays {

  /**
   * See <a href="http://www.wikiwand.com/en/Public_holidays_in_France">http://www.wikiwand.com/en/Public_holidays_in_France</a>.
   */
  FRANCE {

    @Override
    protected void addFixedHolidays(Set<Holiday> holidays) {
      holidays.add(new Holiday(Calendar.JANUARY, 1));
      holidays.add(new Holiday(Calendar.MAY, 1));
      holidays.add(new Holiday(Calendar.MAY, 8));
      holidays.add(new Holiday(Calendar.JULY, 14));
      holidays.add(new Holiday(Calendar.AUGUST, 15));
      holidays.add(new Holiday(Calendar.NOVEMBER, 1));
      holidays.add(new Holiday(Calendar.NOVEMBER, 11));
      holidays.add(new Holiday(Calendar.DECEMBER, 25));
    }

    @Override
    protected void addVariableHolidays(int year, Set<Holiday> holidays) {
      Date easterSunday = getEasterSunday(year);
      holidays.add(new Holiday(getEasterMonday(easterSunday)));
      holidays.add(new Holiday(getAscensionThursday(easterSunday)));
      holidays.add(new Holiday(getPentecostMonday(easterSunday)));
    }

  },

  /**
   * See <a href="http://www.wikiwand.com/en/Public_holidays_in_the_United_Kingdom">http://www.wikiwand.com/en/Public_holidays_in_the_United_Kingdom</a>.
   */
  ENGLAND {

    @Override
    protected void addFixedHolidays(Set<Holiday> holidays) {
      holidays.add(new Holiday(Calendar.JANUARY, 1));
      holidays.add(new Holiday(Calendar.DECEMBER, 25));
      holidays.add(new Holiday(Calendar.DECEMBER, 26));
    }

    @Override
    protected void addVariableHolidays(int year, Set<Holiday> holidays) {
      Date easterSunday = getEasterSunday(year);
      holidays.add(new Holiday(getGoodFriday(easterSunday)));
      holidays.add(new Holiday(getEasterMonday(easterSunday)));
      holidays.add(new Holiday(get(WeekdayIndex.FIRST, Calendar.MONDAY, Calendar.MAY, year)));
      holidays.add(new Holiday(get(WeekdayIndex.LAST, Calendar.MONDAY, Calendar.MAY, year)));
      holidays.add(new Holiday(get(WeekdayIndex.LAST, Calendar.MONDAY, Calendar.AUGUST, year)));
      Holiday christmasDay = new Holiday(Calendar.DECEMBER, 25);
      if (christmasDay.isWeekend(year)) {
        holidays.add(new Holiday(Calendar.DECEMBER, 27));
      }
      Holiday boxingDay = new Holiday(Calendar.DECEMBER, 26);
      if (boxingDay.isWeekend(year)) {
        holidays.add(new Holiday(Calendar.DECEMBER, 28));
      }
    }

  };

  public class HolidayException extends Exception {

    private static final long serialVersionUID = 1L;

    private HolidayException(String message) {
      super(message);
    }

  }

  /**
   * A holiday is defined by a {@link Calendar#MONTH} and a {@link Calendar#DAY_OF_MONTH}.
   */
  private class Holiday {

    private final int day;
    private final int month;

    public Holiday(Date date) {
      Calendar calendar = Calendar.getInstance();
      calendar.setTime(date);
      month = calendar.get(Calendar.MONTH);
      day = calendar.get(Calendar.DAY_OF_MONTH);
    }

    public Holiday(int month, int day) {
      this.month = month;
      this.day = day;
    }

    public Date toDate(int year) {
      Calendar calendar = Calendar.getInstance();
      calendar.set(year, month, day);
      return calendar.getTime();
    }

    public boolean isWeekend(int year) {
      Calendar calendar = Calendar.getInstance();
      calendar.setTime(toDate(year));
      int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
      return dayOfWeek == Calendar.SATURDAY || dayOfWeek == Calendar.SUNDAY;
    }

    @Override
    public boolean equals(Object obj) {
      if (this == obj) {
        return true;
      } else if (!(obj instanceof Holiday)) {
        return false;
      } else {
        Holiday holiday = (Holiday) obj;
        return holiday.month == month && holiday.day == day;
      }
    }

    @Override
    public int hashCode() {
      return Arrays.hashCode(new int[] { month, day });
    }

  }

  /**
   * Use with {@link Holidays#get(WeekdayIndex, int, int, int)}.<br />
   * <br />
   * Example: <code>Holidays.get(WeekdayIndex.FIRST, Calendar.MONDAY, Calendar.MAY, 2000)</code>.
   */
  public enum WeekdayIndex {

    FIRST(1), SECOND(2), THIRD(3), FOURTH(4), LAST(null);

    private final Integer index;

    private WeekdayIndex(Integer index) {
      this.index = index;
    }

    private boolean is(int count) {
      return index != null && index == count;
    }

  }

  private final Set<Holiday> fixedHolidays = new HashSet<Holiday>();

  private final Map<Integer, Set<Holiday>> variableHolidays = new HashMap<Integer, Set<Holiday>>();

  private Holidays() {
    addFixedHolidays(fixedHolidays);
  }

  protected abstract void addFixedHolidays(Set<Holiday> holidays);

  protected abstract void addVariableHolidays(int year, Set<Holiday> holidays);

  /**
   * Returns the number of business days between two dates.
   * 
   * @param d1
   *          The first date.
   * @param d2
   *          The second date.
   * @return The number of business days between the two provided dates.
   * @throws HolidayException
   *           If <code>d1</code> or <code>d2</code> is not a business day.
   */
  public int getBusinessDayCount(Date d1, Date d2) throws HolidayException {
    Calendar calendar = Calendar.getInstance();
    DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
    try {
      d1 = formatter.parse(formatter.format(d1));
      d2 = formatter.parse(formatter.format(d2));
    } catch (ParseException ignore) {
      // cannot happen
    }
    if (!isBusinessDay(d1) || !isBusinessDay(d2)) {
      throw new HolidayException("Input dates must be business days");
    }
    int businessDayCount = 0;
    Date min = d1.before(d2) ? d1 : d2;
    Date max = min.equals(d2) ? d1 : d2;
    calendar.setTime(min);
    while (calendar.getTime().before(max)) {
      calendar.add(Calendar.DAY_OF_MONTH, 1);
      if (isBusinessDay(calendar.getTime())) {
        businessDayCount++;
      }
    }
    return businessDayCount;
  }

  /**
   * Returns whether a date is a business day.
   * 
   * @param date
   *          The date.
   * @return <code>true</code> if the <code>date</code> is a business day, <code>false</code> otherwise.
   */
  public boolean isBusinessDay(Date date) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    int dayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
    if (dayOfWeek == Calendar.SATURDAY || dayOfWeek == Calendar.SUNDAY) {
      return false;
    } else if (isFixedHoliday(date)) {
      return false;
    } else if (isVariableHoliday(date)) {
      return false;
    }
    return true;
  }

  private boolean isFixedHoliday(Date date) {
    return fixedHolidays.contains(new Holiday(date));
  }

  private boolean isVariableHoliday(Date date) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);
    int year = calendar.get(Calendar.YEAR);
    Set<Holiday> yearHolidays;
    if (!variableHolidays.containsKey(year)) {
      // variable holidays have not been calculated for this year yet
      yearHolidays = new HashSet<Holiday>();
      addVariableHolidays(year, yearHolidays);
      variableHolidays.put(year, yearHolidays);
    } else {
      yearHolidays = variableHolidays.get(year);
    }
    return yearHolidays.contains(new Holiday(date));
  }

  public static Date getEasterSunday(int year) {
    // credits: https://www.wikiwand.com/en/Computus#/Anonymous_Gregorian_algorithm
    Calendar calendar = Calendar.getInstance();
    int initialYear = year;
    if (year < 1900) {
      year += 1900;
    }
    int a = year % 19;
    int b = year / 100;
    int c = year % 100;
    int d = b / 4;
    int e = b % 4;
    int f = (b + 8) / 25;
    int g = (b - f + 1) / 3;
    int h = (19 * a + b - d - g + 15) % 30;
    int i = c / 4;
    int j = c % 4;
    int k = (32 + 2 * e + 2 * i - h - j) % 7;
    int l = (a + 11 * h + 22 * k) / 451;
    int m = (h + k - 7 * l + 114) % 31;
    int month = (h + k - 7 * l + 114) / 31 - 1;
    int day = m + 1;
    calendar.set(initialYear, month, day);
    return calendar.getTime();
  }

  public static Date getGoodFriday(Date easterSunday) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(easterSunday);
    calendar.add(Calendar.DAY_OF_MONTH, -2);
    return calendar.getTime();
  }

  public static Date getEasterMonday(Date easterSunday) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(easterSunday);
    calendar.add(Calendar.DAY_OF_MONTH, 1);
    return calendar.getTime();
  }

  public static Date getAscensionThursday(Date easterSunday) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(easterSunday);
    calendar.add(Calendar.DAY_OF_MONTH, 39);
    return calendar.getTime();
  }

  public static Date getPentecostMonday(Date easterSunday) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(easterSunday);
    calendar.add(Calendar.DAY_OF_MONTH, 50);
    return calendar.getTime();
  }

  public static Date get(WeekdayIndex weekdayIndex, int dayOfWeek, int month, int year) {
    Calendar calendar = Calendar.getInstance();
    calendar.set(year, month, 1);
    int count = 0;
    Date last = null;
    do {
      if (calendar.get(Calendar.DAY_OF_WEEK) == dayOfWeek) {
        count++;
        last = calendar.getTime();
        if (weekdayIndex.is(count)) {
          return last;
        }
      }
      calendar.add(Calendar.DAY_OF_MONTH, 1);
    } while (calendar.get(Calendar.MONTH) == month);
    if (weekdayIndex.equals(WeekdayIndex.LAST)) {
      return last;
    }
    return null;
  }

}

Calling with:

Holidays.FRANCE.getBusinessDayCount(d1, d2);

Answer 2

This seems to be a common problem with Date calculations. I often shudder at suggesting to use JodaTime, but it seems to be the de facto Date API for Java. If you want to be adventurous it is trivial to implement a class that has dates based on the year. So we know that in America town that the 4th of July abides by these rules

"Federal law (5 U.S.C. 6103) establishes the following public holidays for Federal employees. Please note that most Federal employees work on a Monday through Friday schedule. For these employees, when a holiday falls on a nonworkday -- Saturday or Sunday -- the holiday usually is observed on Monday (if the holiday falls on Sunday) or Friday (if the holiday falls on Saturday)."

So given this knowledge you could calculate what day of the week a holiday would occur and subtract that value from the number of days between two ranges.