asp.net 上傳單個文件(c#)

HttpFileCollection files  = HttpContext.Current.Request.Files;
HttpPostedFile postedFile = files[0];
string fileName, fileExtension;
fileName = System.IO.Path.GetFileName(postedFile.FileName);
if (fileName != "")
 {
  fileExtension = System.IO.Path.GetExtension(fileName);
///保存上傳文件的文件夾，且需要修改此文件夾的寫入權限
  postedFile.SaveAs(System.Web.HttpContext.Current.Request.MapPath("images/") + fileName);
 }