public class HttpHelper
    {
        public static string contentType = "application/x-www-form-urlencoded";
        public static string accept = "image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-shockwave-flash, application/x-silverlight, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/x-ms-application, application/x-ms-xbap, application/vnd.ms-xpsdocument, application/xaml+xml, application/x-silverlight-2-b1, */*";
        public static string userAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E; Zune 4.7; BOIE9;ZHCN)";
        public static string referer = "";

        /// <summary>
        /// 获取HTML
        /// </summary>
        /// <param name="url"></param>
        /// <param name="cookieContainer"></param>
        /// <param name="method">GET or POST</param>
        /// <param name="postData">like "username=admin&password=123"</param>
        /// <returns></returns>
        public static string GetHtml(string url, CookieContainer cookieContainer = null, string method = "GET", string postData = "")
        {
            cookieContainer = cookieContainer ?? new CookieContainer();

            HttpWebRequest httpWebRequest = null;
            HttpWebResponse httpWebResponse = null;

            try
            {
                httpWebRequest = (HttpWebRequest)HttpWebRequest.Create(url);
                httpWebRequest.CookieContainer = cookieContainer;
                httpWebRequest.ContentType = contentType;
                httpWebRequest.Referer = referer;
                httpWebRequest.Accept = accept;
                httpWebRequest.UserAgent = userAgent;
                httpWebRequest.Method = method;
                httpWebRequest.ServicePoint.ConnectionLimit = int.MaxValue;

                if (method.ToUpper() == "POST")
                {
                    byte[] byteRequest = Encoding.Default.GetBytes(postData);
                    Stream stream = httpWebRequest.GetRequestStream();
                    stream.Write(byteRequest, 0, byteRequest.Length);
                    stream.Close();
                }

                httpWebResponse = (HttpWebResponse)httpWebRequest.GetResponse();
                Stream responseStream = httpWebResponse.GetResponseStream();
                StreamReader streamReader = new StreamReader(responseStream, Encoding.UTF8);
                string html = streamReader.ReadToEnd();

                streamReader.Close();
                responseStream.Close();

                httpWebRequest.Abort();
                httpWebResponse.Close();

                return html;
            }
            catch (Exception)
            {
                return string.Empty;
            }
        }
    }