练习数据校验时为何写了PostMapping 运行时却显示 不支持 post

Question

问题遇到的现象和发生背景

问题相关代码，请勿粘贴截图

controller

    @GetMapping(value = "/add")
    public String add(Model model){
        model.addAttribute("complain",new Complain());
        return "user/complainapply";
    }

    @PostMapping("/add/{id}")
    public String add(@Valid Complain complain, @Valid int id, BindingResult bindingResult){
        User user = adminService.findUserById(id);
        complain.setUser(user);
        complainService.add(complain);
        if (bindingResult.hasErrors()){
            return "user/complainapply";
        }
        return "user/showcomplain";
    }

前端页面
<form:form modelAttribute="complain" action="/complain/add?id=${sessionScope.user.id}">

        <table>
            <tr>
                <td>投诉原因</td>
                <td><form:input path="complain_content"/><form:errors path="complain_content"></form:errors>
                </td>
            </tr>
            <tr>
                <td>创建时间</td>
                <td><form:input path="creat_time"/><form:errors path="creat_time"></form:errors>
                </td>
            </tr>
            <tr>
                <td>投诉人</td>
                <td><input name="name" type="text" value="${sessionScope.user.name}"}>
                </td>
            </tr>
            <tr>
                <td>联系电话</td>
                <td><input name="phone" type="text" value="${sessionScope.user.phone}">
                </td>
            </tr>
        </table>

        <div class="buttons">
            <input value="投 诉" type="submit" style="margin-right:20px; margin-top:20px;">
        </div>

        <br class="clear">
    </form:form>

运行结果及报错内容

我想要达到的结果

Answer 1

<form:form modelAttribute="complain" action="/complain/add?id=${sessionScope.user.id}">
改成
<form:form modelAttribute="complain" action="/complain/add/${sessionScope.user.id}">
post接口的id是url的一部分，不是url参数