C# POST请求demo，contentType 格式：application/x-www-form-urlencoded

/*
 * url:为请求地址
 * postData:请求内容例如："key1=value1&key2=value2&key3=value3"
 */ 
 public static string PostUrl(string url, string postData)
     {
         string result = "";
         try
            {
               HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);

               req.Method = "POST";

               req.ContentType = "application/x-www-form-urlencoded";

               req.Timeout = 800;//请求超时时间

               byte[] data = Encoding.UTF8.GetBytes(postData);

               req.ContentLength = data.Length;

               using (Stream reqStream = req.GetRequestStream())
               {
                   reqStream.Write(data, 0, data.Length);

                   reqStream.Close();
               }

               HttpWebResponse resp = (HttpWebResponse)req.GetResponse();

               Stream stream = resp.GetResponseStream();

               //获取响应内容
               using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
               {
                   result = reader.ReadToEnd();
               }
           }catch(Exception e){}

           return result;
    }