根据出生日期计算年龄

最近在写项目的时候遇到了一个需要根据出生日期计算年龄的问题，今天特意将代码记下来已被后期使用。

  //根据出生日期计算年龄
    public  int getAgeByBirth(String birthDayStr) {
        SimpleDateFormat sdf =   new SimpleDateFormat( "yy-MM-dd" );
        Date birthDay= null;
        try {
            birthDay = sdf.parse(birthDayStr);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        // String str = sdf.format(parse( " 2005-06-09 00:00:00 " );


        int age = 0;
        Calendar cal = Calendar.getInstance();
        if (cal.before(birthDay)) { //出生日期晚于当前时间，无法计算
            throw new IllegalArgumentException(
                    "The birthDay is before Now.It's unbelievable!");
        }
        int yearNow = cal.get(Calendar.YEAR);  //当前年份
        int monthNow = cal.get(Calendar.MONTH);  //当前月份
        int dayOfMonthNow = cal.get(Calendar.DAY_OF_MONTH); //当前日期
        cal.setTime(birthDay);
        int yearBirth = cal.get(Calendar.YEAR);
        int monthBirth = cal.get(Calendar.MONTH);
        int dayOfMonthBirth = cal.get(Calendar.DAY_OF_MONTH);
        age = yearNow - yearBirth;   //计算整岁数
        if (monthNow <= monthBirth) {
            if (monthNow == monthBirth) {
                if (dayOfMonthNow < dayOfMonthBirth) age--;//当前日期在生日之前，年龄减一
            } else {
                age--;//当前月份在生日之前，年龄减一
            }
        }
        return age;
    }

在调用的时候注意：

//根据修改过的出生日期从新计算被保险人的年龄
tSaveLPInsuredSchema.setAge(String.valueOf(getAgeByBirth(mLPInsuredSchema.getBirthDay())));