It's a question of the quantity of the shopping cart.

I'm working on the quantity of the shopping cart. At first, I thought I could just change the quantity to JavaScript and pass the price to the order, but when I think about it, even if I log out and log in again, the quantity should remain changed. Then, I thought that if I changed the quantity, I would have to save the price in db right away, so I did it up to there for now. But I only know how to refresh the page as soon as I change the quantity... I looked it up and said I could use ajax, but I don't know exactly how to use it... In the current controller, when you press the - button, the count becomes -1, and the + button becomes +1, and the page is loaded. I'll post it as a reference below.

@RequestMapping("/cart_update_plus")
    public String cart_update_plus(@RequestParam("status_idx") int status_idx, HttpServletRequest request, Model model) {
        int idx = (int) request.getSession().getAttribute("user_idx");
        int update_plus = iBasketdao.update_plus( idx, status_idx );
        List<BasketDto> list = iBasketdao.list(idx);
        int sum = iBasketdao.sum(idx);
        model.addAttribute("list", list);
        model.addAttribute("sum", sum);
        model.addAttribute("mainPage", "Mypage/cart.jsp");
        return "index";
    }

If you use ajax, I wonder if you have to erase everything you set up on the controller and treat it differently or if you are using ajax. I'm a beginner, so even if I look up the writings about Ajax, I can't understand when I try to apply them to mine. Thank you in advance for your reply.