android银行卡号验证算法详解

public class CheckIdCard {
  /**
   * 校验银行卡卡号
   *
   * @param cardId
   * @return
   */
  public static boolean checkBankCard(String cardId) {
    char bit = getBankCardCheckCode(cardId
        .substring(0, cardId.length() - 1));
    if (bit == 'N') {
      return false;
    }
    return cardId.charAt(cardId.length() - 1) == bit;
  }

  /**
   * 从不含校验位的银行卡卡号采用 Luhm 校验算法获得校验位
   *
   * @param nonCheckCodeCardId
   * @return
   */
  public static char getBankCardCheckCode(String nonCheckCodeCardId) {
    if (nonCheckCodeCardId == null
        || nonCheckCodeCardId.trim().length() == 0
        || !nonCheckCodeCardId.matches("\d+")) {
      // 如果传的不是数据返回N
      return 'N';
    }
    char[] chs = nonCheckCodeCardId.trim().toCharArray();
    int luhmSum = 0;
    for (int i = chs.length - 1, j = 0; i  = 0; i--, j++) {
      int k = chs[i] - '0';
      if (j % 2 == 0) {
        k *= 2;
        k = k / 10 + k % 10;
      }
      luhmSum += k;
    }
    return (luhmSum % 10 == 0) ? '0' : (char) ((10 - luhmSum % 10) + '0');
  }
}