Yii2 UploadedFile上传文件

use yii\web\UploadedFile;

public function actionUpload()
 {
     Yii::$app->response->format = Response::FORMAT_JSON;
     if(Yii::$app->request->isPost) {
         $image = UploadedFile::getInstanceByName('img');
         $imageName = $image->getBaseName();
         $ext = $image->getExtension();
         $rootPath = 'assets/images/';
         $path = $rootPath.date('Y/m/d/');
         if (!file_exists($path)) {
             mkdir($path, 0755, true);
         }
         $fullName = $path.$imageName.$ext;
         if($image->saveAs($fullName)) {
             return ['code'=>1, 'message'=>'保存图片成功', 'data'=>$fullName];
         } else {
             return ['code'=>0, 'message'=>'保存图片失败', 'data'=>$image->error];
         }
     } else {
         return ['code'=>0, 'message'=>'不是POST'];
     }
 }