getStringRandomA

    // 生成随机数字和字母
    // https://blog.csdn.net/yaodong_y/article/details/8115250
    public static String getStringRandomA(int length) {
        String val = "";
        Random random = null;
        // 参数length，表示生成几位随机数
        for (int i = 0; i < length; i++) {
            random = new Random(System.nanoTime());

            String charOrNum = random.nextInt(2) % 2 == 0 ? "char" : "num";
            // 输出字母还是数字
            if ("char".equalsIgnoreCase(charOrNum)) {
                // 输出是大写字母还是小写字母
                int temp = random.nextInt(2) % 2 == 0 ? 65 : 97;
                val += (char) (random.nextInt(26) + temp);
            } else if ("num".equalsIgnoreCase(charOrNum)) {
                val += String.valueOf(random.nextInt(10));
            }
        }
        return val;
    }