向post请求中写入数据，最终保存在了HttpWebRequest.Params中

 　　　　protected void btnLogin_Click(object sender, EventArgs e)
        {
            
            string Url = "http://localhost:18472/DataRequest.aspx";
            string contentType = "application/x-www-form-urlencoded";
            string username = "administrator";
            string password = "admin";
            IDictionary<string,string> param=new Dictionary<string,string>();
            param.Add("username",username);
            param.Add("password",password);
            int i = 0;
            StringBuilder sb=new StringBuilder();
            foreach (var key in param.Keys)
            {
                if (i>0)
                {
                    sb.AppendFormat("&{0}={1}", key, param[key]);
                }
                else
                {
                    sb.AppendFormat("{0}={1}", key, param[key]);
                }
                i++;
            }
            //string content = SendPost(sb.ToString(),Url,contentType);
            string content = SendPost(username,Url,contentType);
        }
        /// <summary>
        /// 
        /// </summary>
        /// <param name="data">写入流中的数据，最后将保存在request.params中，是Idictionary类型的变量；如果是没有等号的string类型，key=null，value=string</param>
        /// <param name="url">请求的url</param>
        /// <param name="contentType">请求的内容类型</param>
        /// <returns></returns>
        public static string SendPost(string data, string url, string contentType)
        {
            string content = string.Empty;
            HttpWebRequest httpWebRequest = WebRequest.Create(url) as HttpWebRequest;
            httpWebRequest.AllowAutoRedirect = true;
            httpWebRequest.Method = "POST";
            httpWebRequest.ContentType = contentType;
            using (StreamWriter sw = new StreamWriter(httpWebRequest.GetRequestStream()))
            {
                sw.Write(data);
            }
            HttpWebResponse httpWebResponse = httpWebRequest.GetResponse() as HttpWebResponse;
            using (StreamReader sr = new StreamReader(httpWebResponse.GetResponseStream(), System.Text.Encoding.Default))
            {
                content = sr.ReadToEnd();
            }
            //httpWebRequest.EndGetResponse;
            return content;
        }

       string content="";
　　　　using (Stream stream = HttpContext.Current.Request.InputStream)
       {
           using (StreamReader sr = new StreamReader(stream, Encoding.UTF8))
           {
                content=sr.ReadToEnd();
           }
       }                    

string XML=content;
HttpContext context=HttpContext.Current;
context.Items.Add("XML", XML); 

string XML=context.Items["XML"].ToString();