根据生日获取年龄或者预产期

/**
 * 根据生日获取年龄或者预产期
 *
 * @param birthday
 * @return
 * @throws ParseException
 */
public static String getAge(Date birthday) throws ParseException {
    StringBuffer str = new StringBuffer();
    // 取今天时间
    Calendar Calendartoday = Calendar.getInstance();
    if (birthday.getTime() > Calendartoday.getTime().getTime()) {
        long daysBetweennumber = daysBetween(Calendartoday.getTime(), birthday);
        long pregnantDays = 280 - daysBetweennumber;
        // 算出多少周
        int WeekBetweennumber = (int) pregnantDays / 7;
        // 零多少天
        long dayNumber = pregnantDays % 7;
        str.append("孕");
        if (WeekBetweennumber > 0) {
            str.append(WeekBetweennumber + "周");
        }
        if (dayNumber > 0) {
            str.append(dayNumber + "天");
        }
    } else {
        Calendar calendar = GregorianCalendar.getInstance();
        calendar.setTime(birthday);

        Calendar now = Calendar.getInstance();

        int day = now.get(Calendar.DAY_OF_MONTH) - calendar.get(Calendar.DAY_OF_MONTH);

        int month = now.get(Calendar.MONTH) - calendar.get(Calendar.MONTH);

        int year = now.get(Calendar.YEAR) - calendar.get(Calendar.YEAR);
        /**
         *  按照减法原理，先day相减，不够向month借；然后month相减，不够向year借；最后year相减。
         */
        if (day < 0) {
            month -= 1;
            now.add(Calendar.MONTH, -1);//得到上一个月，用来得到上个月的天数。
            day = day + now.getActualMaximum(Calendar.DAY_OF_MONTH);
        }
        if (month < 0) {
            month = (month + 12) % 12;
            year--;
        }
        if (year > 0) {
            str.append(year + "岁");
        }
        if (month > 0) {
            str.append(month + "个月");
        }
        if (day > 0) {
            str.append(day + "天");
        }
        /**
         * 当预产期或者生日是当天则显示孕40周
         */
        if (StringUtil.isNullOrEmpty(str.toString())) {
            str.append("孕40周");
        }
    }
    return str.toString();

}