UUID随机验证码

代码：

 public static void main(String[] args) {
        //随机验证码
        //5位数的随机数 UUID生成的是16进制的
        String res = UUID.randomUUID().toString();
        res=res.substring(0,5);
        System.out.println(res);
        System.out.println("-----------");


        String str="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        str+=str.toLowerCase();
        str+="0123456789";
        //从所有的字符中随机称5个
     /*   int index = new Random().nextInt(str.length());
        System.out.println(str.charAt(index));*/

        StringBuilder stringBuilder = new StringBuilder(5);
        //随机取5个
        for (int i = 0; i < 5; i++) {
            int index = new Random().nextInt(str.length());
            char ch = str.charAt(index);
            stringBuilder.append(ch);
        }
        System.out.println(stringBuilder);
    }