Laravel控制器无法保存来自ajax请求的文件

<meta name="csrf-token" content="{{ csrf_token() }}">

$.ajaxSetup({
    headers: {
        'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
    }
});

Route::post('/upload', 'UploadController@upload')->middleware('csrf');

use Illuminate\Http\Request;

class UploadController extends Controller
{
    public function upload(Request $request)
    {
        if ($request->hasFile('file')) {
            $file = $request->file('file');
            $file->store('path/to/save');
            return response()->json(['success' => true]);
        }
        return response()->json(['success' => false]);
    }
}