1、直接使用hutool工具类计算年龄

int age(Date begin,Date end) 表示出生到去世的年龄
int ageOfNow(String birthday) 计算到当前时间的年龄
int ageOfNow(Date birthday) 计算到当前时间的年龄

2、手搓 自己写

public Integer getAge(Date dateOfBirth) {
    Integer age = 0;
    Calendar born = Calendar.getInstance();
    Calendar now = Calendar.getInstance();
    if (dateOfBirth != null) {
        now.setTime(new Date());
        born.setTime(dateOfBirth);
        if (born.after(now)) {
            throw new IllegalArgumentException("年龄不能超过当前日期");
        }
        age = now.get(Calendar.YEAR) - born.get(Calendar.YEAR);
        int nowDayOfYear = now.get(Calendar.DAY_OF_YEAR);
        int bornDayOfYear = born.get(Calendar.DAY_OF_YEAR);
        if (nowDayOfYear < bornDayOfYear) {
            age -= 1;
        }
    }
    return age;
}