新建一个Request抽象类，其他的Request都继承于它

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;
use Illuminate\Contracts\Validation\Validator;
use Illuminate\Http\Exceptions\HttpResponseException;

abstract class Request extends FormRequest{
    protected function failedValidation(Validator $validator)
    {
        $errormsg = $validator->errors()->messages();
        foreach ($errormsg  as $item) {
            $msg = current($item);
            break;
        };

        throw (new HttpResponseException(response()->json([
            'code' => 1,
            'message' => $msg,
        ], 422)));
    }
}

使用示例

namespace App\Http\Requests; 

class UserRequest extends Request{  
    public function rules()
    {
        return [
          "username" => "required|string",
          "password" => "required|string|min:6"
        ];
    }
    
    public function messages()
    {
      return [
        "username.requried" => "请填写用户名",
        "username.string" => "用户名必须为字符串",
        "password.required" => "请填写密码",
        "password.string" => "密码必须为字符串",
        "password.min" => "密码不少于6位"
      ];
    }
}