string字符串得到生日

private static int getAge(String birthDate) throws Exception {
		SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
		Calendar calBirth = Calendar.getInstance();
		calBirth.setTime(sdf.parse(birthDate));
		Calendar cal = Calendar.getInstance();
		int yearDiff = cal.get(Calendar.YEAR) - calBirth.get(Calendar.YEAR);
		calBirth.add(Calendar.YEAR, yearDiff);
		if (cal.getTimeInMillis() - calBirth.getTimeInMillis() < 0) {
			return yearDiff - 1;
		}
		return yearDiff;
	}