class ApiCommController extends Controller
{

    public function behaviors()
    {
        $behaviors = parent::behaviors();
        $behaviors['contentNegotiator']['formats']['text/html'] = Response::FORMAT_JSON;
        return $behaviors;

    }
}

原后你就可以看看了。

或者controller 添加

Yii::$app->response->format = \yii\web\Response::FORMAT_JSON;

自己封装实现，