C# http get请求 判断是否存在该图片信息

 /// <summary>
    /// http get请求
    /// </summary>
    /// <param name="Url"></param>
    /// <param name="postDataStr"></param>
    /// <returns></returns>
    public string HttpGet(string Url, string postDataStr)
    {
        string retString = string.Empty;
        try
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url + postDataStr);
            request.Method = "GET";
            request.ContentType = "text/html;charset=UTF-8";

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream myResponseStream = response.GetResponseStream();
            StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
            retString = myStreamReader.ReadToEnd();
            myStreamReader.Close();
            myResponseStream.Close();
        }

        catch (Exception ex)
        {
            if (!File.Exists(Server.MapPath("~/LogFile/" + DateTime.Now.ToString("yyyy-MM") + ".txt")))
            {
                FileStream fs = new FileStream(Server.MapPath("~/LogFile/" + DateTime.Now.ToString("yyyy-MM") + ".txt"), FileMode.Create, FileAccess.Write); //可以指定盘符，也可以指定任意文件名，还可以为word等文件
                StreamWriter sw = new StreamWriter(fs); // 创建写入流
                sw.WriteLine(ex.Message); // 写入Hello World
                sw.Close(); //关闭文件
            }
            else
            {
                FileStream fs = new FileStream(Server.MapPath("~/LogFile/" + DateTime.Now.ToString("yyyy-MM") + ".txt"), FileMode.Open, FileAccess.Write);
                StreamWriter sr = new StreamWriter(fs);
                sr.WriteLine(ex.Message);//开始写入值
                sr.Close();
                fs.Close();
            }
        }
        
        return retString;
    }