计算年龄java

public static String getAge(String birthDayStr) {
        try {
            if (StringUtil.isBlank(birthDayStr)) {
                return "";
            }
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
            Date birthDay = sdf.parse(birthDayStr);
            Calendar cal = Calendar.getInstance();
            if (cal.before(birthDay)) {
                throw new IllegalArgumentException("The birthDay is before Now.It's unbelievable!");
            }
            int yearNow = cal.get(Calendar.YEAR);
            int monthNow = cal.get(Calendar.MONTH);
            int dayOfMonthNow = cal.get(Calendar.DAY_OF_MONTH);
            cal.setTime(birthDay);
            int yearBirth = cal.get(Calendar.YEAR);
            int monthBirth = cal.get(Calendar.MONTH);
            int dayOfMonthBirth = cal.get(Calendar.DAY_OF_MONTH);
            int age = yearNow - yearBirth;
            if (monthNow <= monthBirth) {
                if (monthNow == monthBirth) {
                    if (dayOfMonthNow < dayOfMonthBirth)
                        age--;
                } else {
                    age--;
                }
            }
            return String.valueOf(age);
        } catch (Exception e) {
            return "";
        }
    }