Lumen框架调用successResponse()出现未定义的500错误求助

我是后端初学者，授课老师提供的视频没涵盖CRUD操作内容，自己摸索实现POST接口时，遇到了错误：Call to undefined method App\Http\Controllers\UserController::successResponse() (500 Internal Server Error)。以下是相关代码和请求数据，无法定位错误原因，求帮忙解决。

控制器代码（UserController.php） #

<?php
namespace App\Http\Controllers;
use Illuminate\Http\Request;
use App\Models\User;

Class UserController extends Controller {
    private $request;

    public function __construct(Request $request){
        $this->request = $request;
    }

    public function getUsers(){ 
        $users = User::all();
        return response()->json($users, 200);
    }

    public function add(Request $request ){
        $rules = [
            'first_name' => 'required|max:20',
            'last_name' => 'required|max:20',
            // 'gender' => 'required|in:Male,Female',
        ];
        $this->validate($request,$rules);
        $user = User::create($request->all());
        return $this->successResponse($user, Response::HTTP_CREATED);
    }
} 

模型代码（User.php） #

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class User extends Model{
    public $timestamps = false;
    protected $table = 'students';
    // 允许批量赋值的字段
    protected $fillable = [
        'first_name', 'last_name'
    ];
}

路由代码（web.php） #

<?php

/** @var \Laravel\Lumen\Routing\Router $router */

/*
|--------------------------------------------------------------------------
| Application Routes
|--------------------------------------------------------------------------
|
| Here is where you can register all of the routes for an application.
| It is a breeze. Simply tell Lumen the URIs it should respond to
| and give it the Closure to call when that URI is requested.
|
*/

$router->get('/', function () use ($router) {
    return $router->app->version();
});

$router->get('/users',['uses' => 'UserController@getUsers']);

$router->post('/postUsers', 'UserController@add'); // 创建新用户记录

Postman发送的POST请求数据 #

{
    "first_name": "Lorem",
    "last_name": "Ipsum"
}

• 错误核心：你的UserController调用了successResponse()方法，但这个方法不存在于你继承的基础Controller类中（Lumen默认的基础控制器没有封装这个方法）。
• 两种解决方式：
  1. 改用Lumen原生响应写法：
     将add方法里的返回语句替换为：

     return response()->json($user, \Illuminate\Http\Response::HTTP_CREATED);
     

     如果顶部没引入Response类，记得添加：

     use Illuminate\Http\Response;
     

  2. 自定义successResponse()方法：
     在UserController中添加这个方法（或者在全局基础Controller里定义，方便其他控制器复用）：

     protected function successResponse($data, $statusCode = 200)
     {
         return response()->json($data, $statusCode);
     }
     

• 额外提示：控制器构造函数已经注入了Request，但add方法又重复注入，可选择去掉构造函数的注入，直接用方法参数的Request，避免代码冗余。

内容的提问来源于stack exchange，提问作者Coder