C#封装：从网络下载并保存多种图片类型到本地

/// <summary>
        /// 保存web图片到本地
        /// </summary>
        /// <param name="imgUrl">web图片路径</param>
        /// <param name="path">保存路径</param>
        /// <param name="fileName">保存文件名</param>
        /// <returns></returns>
        public static string SaveImageFromWeb(string imgUrl, string path, string fileName)
        {
            if (path.Equals(""))
                throw new Exception("未指定保存文件的路径");
            string imgName = imgUrl.ToString().Substring(imgUrl.ToString().LastIndexOf("/") + 1);
            string defaultType = ".jpg";
            string[] imgTypes = new string[] { ".jpg", ".jpeg", ".png", ".gif", ".bmp" };
            string imgType = imgUrl.ToString().Substring(imgUrl.ToString().LastIndexOf("."));
            string imgPath = "";
            foreach (string it in imgTypes)
            {
                if (imgType.ToLower().Equals(it))
                    break;
                if (it.Equals(".bmp"))
                    imgType = defaultType;
            }

            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(imgUrl);
            request.UserAgent = "Mozilla/6.0 (MSIE 6.0; Windows NT 5.1; Natas.Robot)";
            request.Timeout = 3000;

            WebResponse response = request.GetResponse();
            Stream stream = response.GetResponseStream();