var code = request.getSession.getAttribute("code");

I added this sentence to the js method. I want to get the code sent from the background, and then the js introduced will be invalid. After unchecking it, it can run normally.
Please give me an answer.

public String mailcode(String mail,HttpServletRequest request) throws Exception{
        RegisterPojo registerPojo = registerService.findBymail(mail);
        if(registerPojo == null){
            //生成四位随机数字
            Random random = new Random();
            int code = random.nextInt(9999-1000+1)+100;
            String mailcode = String.valueOf(code);
            Main.main(mail, mailcode);
            HttpSession session = request.getSession();
            session.setAttribute("code", mailcode);
             return mailcode;
        }
            return "";
            
    }