///作用：FileUpLoad 上传大文件使用.net 的FileUpLoad 控件上传文件非常的方便, 在Web.config 中的<System.web>下添加如下的语句
   <system.web>
    <httpRuntime maxRequestLength="1000000" executionTimeout="45"/>
   </system.web>
maxRequestLength 的单位为字节，executionTimeout的单位为秒

//upload code:
     Boolean fileOK = false;
            String path = Server.MapPath("~/Images/");
            if (FileUpload1.HasFile)
            {
                String fileExtension = System.IO.Path.GetExtension(FileUpload1.FileName).ToLower();
                String[] allowedExtensions = { ".gif", ".png", ".jpeg", ".jpg" };
                for (int i = 0; i < allowedExtensions.Length; i++)
                {
                    if (fileExtension == allowedExtensions[i])
                    {
                        fileOK = true;
                    }
                }
            }

            if (fileOK)
            {
                try
                {
                    FileUpload1.PostedFile.SaveAs(path
                        + FileUpload1.FileName);
                    Label1.Text = "File uploaded!";
                }
                catch (Exception ex)
                {
                    Label1.Text = "File could not be uploaded.";
                }
            }
            else
            {
                Label1.Text = "Cannot accept files of this type.";
            }