java根据身份证号或生日计算年龄

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

/**
 * AgeUtil
 *
 * 根据身份证号或生日计算年龄
 *
 */
public class AgeUtil {

  private static final int invalidAge = -1; // 非法的年龄，用于处理异常。

  /**
   * 根据身份证号码计算年龄
   *
   * @param idNumber 考虑到了15位身份证，但不一定存在
   */
  public static int getAgeByIDNumber(String idNumber) {
    String dateStr;
    if (idNumber.length() == 15) {
      dateStr = "19" + idNumber.substring(6, 12);
    } else if (idNumber.length() == 18) {
      dateStr = idNumber.substring(6, 14);
    } else {//默认是合法身份证号，但不排除有意外发生
      return invalidAge;
    }

    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd");
    try {
      Date birthday = simpleDateFormat.parse(dateStr);
      return getAgeByDate(birthday);
    } catch (ParseException e) {
      return invalidAge;
    }

  }

  /**
   * 根据生日计算年龄
   *
   * @param dateStr 这样格式的生日 1990-01-01
   */
  public static int getAgeByDateString(String dateStr) {
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
    try {
      Date birthday = simpleDateFormat.parse(dateStr);
      return getAgeByDate(birthday);
    } catch (ParseException e) {
      return invalidAge;
    }
  }


  public static int getAgeByDate(Date birthday) {
    Calendar calendar = Calendar.getInstance();

    // calendar.before()有的点bug
//    if (calendar.before(birthday)) {
//      return invalidAge;
//    }
    if (calendar.getTimeInMillis() - birthday.getTime() < 0L) {
      return invalidAge;
    }

    int yearNow = calendar.get(Calendar.YEAR);
    int monthNow = calendar.get(Calendar.MONTH);
    int dayOfMonthNow = calendar.get(Calendar.DAY_OF_MONTH);

    calendar.setTime(birthday);

    int yearBirthday = calendar.get(Calendar.YEAR);
    int monthBirthday = calendar.get(Calendar.MONTH);
    int dayOfMonthBirthday = calendar.get(Calendar.DAY_OF_MONTH);

    int age = yearNow - yearBirthday;

    if (monthNow <= monthBirthday) {
      if (monthNow == monthBirthday) {
        if (dayOfMonthNow < dayOfMonthBirthday) {
          age--;
        }
      } else {
        age--;
      }
    }

    return age;
  }
}

参考链接:
通过出生日期获取年龄的方法--Java
http://www.cnblogs.com/wyf-love-dch/p/7483094.html

java根据身份证号或生日计算年龄
https://www.jianshu.com/p/2c33965551c8