request = (HttpWebRequest)WebRequest.Create(url);
                                        if (Const.session != null)
                {
                    request.Headers.Add("Cookie", Const.session);
                }
                request.Timeout = 30000; //设定超时值
                request.ContentType = "application/octet-stream";
                request.Method = "POST";
                request.ContentLength = outData.Length;

stream = request.GetRequestStream();
                stream.Write(outData, 0, outData.Length);
                stream.Flush();
                stream.Close();
                Const.uiWaitMessage = "请求发送完毕，开始接收数据";
                Thread.Sleep(500);
                //发送完毕
                //接收数据
                response = (HttpWebResponse)request.GetResponse();
                if (Const.session == null)
                {// 注销后要清除Common.session
                    String cookie = response.GetResponseHeader("Set-Cookie");
                    if (cookie != null)
                    {
                        int n = cookie.IndexOf(';');
                        if (n > -1)  Const.session = cookie.Substring(0, n);
                    }
                }

使用

if (Const.session == null)
                {// 注销后要清除Common.session
                    String cookie = response.GetResponseHeader("Set-Cookie");
                    if (cookie != null)
                    {
                        int n = cookie.IndexOf(';');
                        if (n > -1)  Const.session = cookie.Substring(0, n);
                    }
                }

可以获得并保存网站分配的Session信息

这样每次访问指定url的时候就可以先用

if (Const.session != null)
                {
                    request.Headers.Add("Cookie", Const.session);
                }

来添加Cookie，将已获得Session信息发送到网站。