js提交form表单，表单中的文件流传不到平台中，遇到过的大神帮帮忙。

1. 这一段是form表单的代码    <form id="uploadForm" action="http://localhost:8080/mashWebServices/propertiesService?method.name=addAppProperties&user.sessionId=23487953159993119854f780276543b848c4c6afbfb&insert._id=4fa12b250b178dfcd9a00fd2" method="post" enctype="multipart/form-data" name="form1">
  <input type="file" name="file">
  <input type="submit" value="上传" id="fileManager_folder" >
</form>action中调用的servlet能拿到对应的file对象2.由于sessionId和_id从参数是动态的，所以想要用js提交form表单。<form id="uploadForm" action="" method="post" enctype="multipart/form-data" name="form1">
  <input type="file" name="file">
  <input type="button" value="上传" onclick="uploadProperties(this)" id="fileManager_folder" >
</form>
js提交form代码：function uploadProperties(obj) {
var uploadForm = $("#uploadForm");
uploadForm.attr("action","http://localhost:8080/mashWebServices/propertiesService?method.name=addAppProperties&user.sessionId=" + top.User.sessionId + "&insert._id=" + obj.id);

uploadForm.submit();