在javaweb增删改查案例中，修改功能不能获得id

Question

问题遇到的现象和发生背景

在这个案例中实现修改功能，点击修改，想获取id，但每次获取的id位null

问题相关代码，请勿粘贴截图

   //修改数据
            updateBrand(){
                var _this=this;
                axios({
                    method: "post",
                    url:"http://localhost:8080/brand-case/brand/update",
                    data:_this.brand,
                }).then(function (resp) {
                    if(  resp.data == "success")
                    {
                        _this.dialogVisible = false;
                        // 重新查询数据
                        _this.selectAll();
                        // 弹出消息提示
                        _this.$message({
                            message: '恭喜你，修改成功',
                            type: 'success'
                        });
                    }
                })


 public void update(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
    {
        BufferedReader br = req.getReader();
        String params = br.readLine();
        Brand brand = JSON.parseObject(params,Brand.class);
        Integer id =(Integer) brand.getId();
        brandService.update(brand,id);
        resp.getWriter().write("success");

    }

//Brand类
public class Brand {
    // id 主键
    private Integer id;
    // 品牌名称
    private String brandName;
    // 企业名称
    private String companyName;
    // 排序字段
    private Integer ordered;
    // 描述信息
    private String description;
    // 状态：0：禁用  1：启用
    private Integer status;


    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getBrandName() {
        return brandName;
    }

    public void setBrandName(String brandName) {
        this.brandName = brandName;
    }

    public String getCompanyName() {
        return companyName;
    }

    public void setCompanyName(String companyName) {
        this.companyName = companyName;
    }

    public Integer getOrdered() {
        return ordered;
    }

    public void setOrdered(Integer ordered) {
        this.ordered = ordered;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public Integer getStatus() {
        return status;
    }
    //逻辑视图
    public String getStatusStr(){
        if (status == null){
            return "未知";
        }
        return status == 0 ? "禁用":"启用";
    }

    public void setStatus(Integer status) {
        this.status = status;
    }

    @Override
    public String toString() {
        return "Brand{" +
                "id=" + id +
                ", brandName='" + brandName + '\'' +
                ", companyName='" + companyName + '\'' +
                ", ordered=" + ordered +
                ", description='" + description + '\'' +
                ", status=" + status +
                '}';
    }
}

运行结果及报错内容

当点击修改后，这条数据会传回，按理说应该会有id.我直接调用brand.getId（），就直接获得了Id,为什么实际会是Null呢

我的解答思路和尝试过的方法

我想要达到的结果

Answer 1

你可以在前端打印一下：_this.brand，看是不是真的把值传递进来了