//生成六位随机验证码
    public static String randomCode(){
        String sources = "0123456789";
        Random random = new Random();
        StringBuffer flag= new StringBuffer();
        // 验证码有几位就循环几次
        for (int j=0;j<6;j++){
            flag.append(sources.charAt(random.nextInt(9))+"");
        }

        return  flag.toString();
    }