根据对于uuid随机获取其index的值组成字符串。生成的字符串越长，唯一性越高。

        int i = 10;
        String uuid = UUID.randomUUID().toString().replace("-", "");
        StringBuilder randomStr = new StringBuilder();
        Random random = new Random();
        for (int j = 0; j < i; j++) {
            int index = random.nextInt(uuid.length());
            System.out.println("获取随机下标：" + index);
            randomStr.append(uuid.charAt(index));
        }
        System.out.println("生成" + i + "位随机数：" + randomStr);