上传文件，比较完善

protected void btnfileup_Click(object sender, EventArgs e)
   {
       try
       {
           if (FileUpload1.PostedFile.FileName == "")
           {
               Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('文件名称不能为空！');</script>");
               return;
           }
           else
           {
               FileUpload1.PostedFile.SaveAs(Server.MapPath("file/" + FileUpload1.PostedFile.FileName.Substring(FileUpload1.PostedFile.FileName.LastIndexOf("\\")+1)));
               Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('上传成功！');</script>");
           }
       }
       catch (Exception ex)
       {

           Response.Write(ex.Message.ToString());
           Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('上传失败！');</script>");

       }
   }