Java 传入时间如“2007-09-01”格式计算出年龄

public static int getAge(Date birthDay) throws Exception {
  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);// 给时间赋值
  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) {
    // monthNow==monthBirth
    if (dayOfMonthNow < dayOfMonthBirth) {
     age--;
    } else {
     // do nothing
    }
   } else {
    // monthNow>monthBirth
    age--;
   }
  } else {
   // monthNow<monthBirth
   // donothing
  }

  return age;
 }