在WebService下为什么HttpContent是Null，如何解决？

Question

public class WebService1 : System.Web.Services.WebService {        [WebMethod(EnableSession = false)]
        
        public void jsMessage() {
            Thread thead = new Thread(new ThreadStart(Tasks.Start));
            thead.Start();
        }
    }    public class Tasks {
        private static readonly string filePath = @"D:\Background.txt";        public static void Start() {
            if (!File.Exists(HttpContext.Current.Server.MapPath("../Config/Warrant/warrant-key.config"))) {
                StreamWriter sw = new StreamWriter(filePath, true);
                sw.WriteLine("{0}\n", DateTime.Now.ToString());
                sw.Flush();
                sw.Close();
            }
            WriteFile();
        }        public static void WriteFile() {
            string url = "http://www.hnrcsc.com/firstPage/showDwzpDetail.asp?dwid=3577";
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            // Downloads the XML file from the specified server.
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            System.IO.StreamReader sr = new StreamReader(response.GetResponseStream(), System.Text.Encoding.UTF8);
            string adf = sr.ReadToEnd();
            sr.Close();
            response.Close();                        MyITJob.Admin.Collection_Thead ccc = new MyITJob.Admin.Collection_Thead();
            ccc.URL = url;
            string a = ccc.TheadColl();
        }
    }