Vue cli向后端发送请求出现错误

Access to XMLHttpRequest at ‘http://localhost:8989/vue/user/findOne?id=2’ from origin ‘http://localhost:8080’ has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource

问题排查

1. 前端发送请求链接错误（少写了项目名或者端口写错）

   findOne(){
         
         
            this.$http.get("http://localhost:8989/vue/user/findOne?id="+this.user.id).then(res=>{
         
         
              console.log(res.data);
              this.user = res.data;
            })
          },
   

2. 后端忘记书写Mappering请求或者请求方式 错误
   例如 post 跟 get 方式错误

   /**
     * 根据id查询用户信息
     */
    @GetMapping("findOne")
    public User findOne(String id) {
         
         
      return userService.findById(id);
    }