身份证验证

public class IdentityUtil {
  // wi =2(n-1)(mod 11);加权因子
  final int[] wi = { 7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2, 1 };
  // 校验码
  final int[] vi = { 1, 0, 'X', 9, 8, 7, 6, 5, 4, 3, 2 };
  private int[] ai = new int[18];

  public IdentityUtil() {
  }

  // 校验身份证的校验码
  public boolean verify(String idcard) {
   if (idcard.length() == 15) {
    idcard = uptoeighteen(idcard);
   }
   if (idcard.length() != 18) {
    return false;
   }
   String verify = idcard.substring(17, 18);
   if (verify.equals(getVerify(idcard))) {
    return true;
   }
   return false;
  }

  // 15位转18位
  public String uptoeighteen(String fifteen) {
   StringBuffer eighteen = new StringBuffer(fifteen);
   eighteen = eighteen.insert(6, "19");
   return eighteen.toString();
  }

  // 计算最后一位校验值
  public String getVerify(String eighteen) {
   int remain = 0;
   if (eighteen.length() == 18) {
    eighteen = eighteen.substring(0, 17);
   }
   if (eighteen.length() == 17) {
    int sum = 0;
    for (int i = 0; i < 17; i++) {
     String k = eighteen.substring(i, i + 1);
     ai[i] = Integer.valueOf(k);
    }
    for (int i = 0; i < 17; i++) {
     sum += wi[i] * ai[i];
    }
    remain = sum % 11;
   }
   return remain == 2 ? "X" : String.valueOf(vi[remain]);

  }
}