利用session来完成购物车功能

public void stockpileSession(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    JsonMsg jsonMsg = new JsonMsg();
    String mealpriceId = request.getParameter("id");
    //根据菜品id获取酒菜详情
    Sys_small meal = this.mealTree.selectmeal(Integer.valueOf(mealpriceId));

   HttpSession session = request.getSession();
    //获取session中的值
    List<Sys_small> small_cart= (List<Sys_small>) session.getAttribute(ProjectParameter.SESSION_SMALL);
    if(small_cart==null){
        //给他添加一个数量
        meal.setNumbersmall(1);
        small_cart=new ArrayList<>();
        small_cart.add(meal);
        session.setAttribute(ProjectParameter.SESSION_SMALL,small_cart);
    }else{
        int selectid = Integer.valueOf(mealpriceId);
        //获取到所有的session数据
        List<Sys_small> smallList = (List<Sys_small>) session.getAttribute(ProjectParameter.SESSION_SMALL);
        //在这里判断是添加新的数据行还是给numbersmall+1
        for (int i=1;i<smallList.size();i++){
            Sys_small home = smallList.get(i);
            if (home.getId()==selectid){
                home.setNumbersmall(home.getNumbersmall()+1);jsonMsg.setState(true);
                jsonMsg.setMsg("添加成功");
                returnJson(response,jsonMsg);
                return;
            }else{

            }
        }
        //给他添加一个数量
        meal.setNumbersmall(1);
        small_cart.add(meal);
        session.setAttribute(ProjectParameter.SESSION_SMALL,small_cart);

    }


    jsonMsg.setState(true);
    jsonMsg.setMsg("添加成功");

        //根据获取到的菜品id查看购物车的数据库中是否存在着相同的菜品，如果存在就菜品数量+1，反之就是整体+1
       // Boolean winKing = this.winKing.intmealTree(meal,existTree, Integer.valueOf(mealpriceuserId));
       // msg.setState(winKing);
        returnJson(response,jsonMsg);
}