/// <summary>

    /// WebClient的扩展

    /// </summary>

    public class webClient : WebClient

    {

        /// <summary>是否重定向 默认为true</summary>

        public bool AllowAutoRedirect { get; set; }

        /// <summary>

        ///获取或设置 Referer HTTP 标头的值。默认值为 null。

        /// </summary>

        public string Referer { get; set; }

        /// <summary>

        /// 获取或设置 Content-type HTTP 标头的值。 默认: application/x-www-form-urlencoded

        /// </summary>

        public string ContentType { get; set; }

        /// <summary>

        /// 获取或设置 User-agent HTTP 标头的值。默认:Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0)

        /// </summary>

        public string UserAgent { get; set; }

        /// <summary>

        /// 获取或设置 GetResponse 和 GetRequestStream 方法的超时值（以毫秒为单位）。 默认值是 30,000 毫秒（30 秒）。

        /// </summary>

        public int Timeout { get; set; }

        /// <summary>

        /// 获取或设置写入或读取流时的超时（以毫秒为单位）。默认值为 300,000 毫秒（5 分钟）

        /// </summary>

        public int ReadWriteTimeout { get; set; }

        /// <summary>获取或设置请求相关联的Cookie</summary>

        public CookieContainer CookieContainer { get; set; }

        /// <summary>创建一个新的 WebClient 实例。</summary>

        public webClient()

        {

            this.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0)";

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

            this.CookieContainer = new CookieContainer();

            this.AllowAutoRedirect = true;

            this.Timeout =  * ;

            this.ReadWriteTimeout =  * ;

        }

        protected override WebRequest GetWebRequest(Uri address)

        {

            HttpWebRequest request = (HttpWebRequest)base.GetWebRequest(address);

            if (this.Referer != null) request.Referer = this.Referer;

            if (this.ContentType != null) request.ContentType = this.ContentType;

            if (this.UserAgent != null) request.UserAgent = this.UserAgent;

            request.AllowAutoRedirect = this.AllowAutoRedirect;

            request.CookieContainer = this.CookieContainer; //这句很关键，有了他可以保存返回的Cookie

            request.Timeout = this.Timeout;

            request.ReadWriteTimeout = this.ReadWriteTimeout;

            return request;

        }

    }