PHP导出EXCEL文件时总是自动打开，请问如何防止？

 header("Content-Type:   application/vnd.ms-excel; charset=utf-8");
    header("Content-Disposition: attachment; filename=$outputFileName");
    header("Expires: 0");
    header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
    header("Cache-Control: private", false);
    $xlsWriter->save("php://output");