只验证了18位

public static boolean isValid(String str) {  
        if (str == null || str.length() != 18) {
            return false;
        }

        int WEIGHTS[] = {
                7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2
        };
        char CHECK[] = {
                '1', '0', 'X', '9', '8', '7', '6', '5', '4', '3', '2'
        };
        int sum = 0;
        for (int index = 0; index < 17; index++) {
            if (str.charAt(index) < '0' || str.charAt(index) > '9') {
                return false;
            }
            sum += str.charAt(index) * WEIGHTS[index];
        }
        if (CHECK[sum % 11] != Character.toUpperCase(str.charAt(str.length() - 1))) {
            return false;
        }

        return true;
    }