.NET自动识别HttpWebResponse的编码及是否压缩

最近项目使用HttpWebRequest请求网页，处理HttpWebResponse返回消息体，发现网页可能是有GZIP压缩等，所得数据乱码，所以相处了解决方案，大家共同学习。
这里是GET方式，POST方式的响应数据基本一样处理即可。
代码：
 /// <summary>
        /// 获取请求信息（get方式）
        /// </summary>
        /// <param name="strUrl">请求的地址</param>
        /// <returns>请求的结果</returns>
        public static string HttpRequestByGet(string strUrl)
        {
            string html = "";
            //拼写请求主体地址
            string RequestString = strUrl;

            //生成请求对象
            HttpWebRequest httprequestPost = (HttpWebRequest)WebRequest.Create(RequestString);

            //设置请求对象属性
            httprequestPost.Method = "get";
            httprequestPost.ContentType = "application/Text/xml";
            ////生成响应对象
            HttpWebResponse res = (HttpWebResponse)httprequestPost.GetResponse();
            ////读取返回数据流（编码格式UFT8）
            Stream responseStream = null;
            if ("gzip".Equals(res.ContentEncoding))
            {
                responseStream = new System.IO.Compression.GZipStream(res.GetResponseStream(), System.IO.Compression.CompressionMode.Decompress);
            }
            else if ("deflate".Equals(res.ContentEncoding))
            {
                responseStream = new System.IO.Compression.DeflateStream(res.GetResponseStream(), System.IO.Compression.CompressionMode.Decompress);
            }
            else
            {
                responseStream = res.GetResponseStream();
            }
            if (responseStream != null)
            {
                StreamReader streamReader = new StreamReader(responseStream, Encoding.GetEncoding(res.CharacterSet));
                html = streamReader.ReadToEnd().Trim();
            }
            //返回结果
            return html;
        }