[转][C#]抓取网页内容

一个很简单的需求，关键代码如下：

private string GetHtml(string item)
{
    // set remote certificate Validation auto pass
    ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(remoteCertificateValidate);
    ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;

    string webSite = item;
    HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(webSite);
    req.KeepAlive = false;
    req.ProtocolVersion = HttpVersion.Version11;
    //req.AllowAutoRedirect = false;   // 不允许自动重定向
    req.Method = "GET";
    req.Timeout = 15 * 1000;    // 传入是秒，需要转换成毫秒
    req.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8";
    req.UserAgent = "Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.121 Safari/537.36";

    HttpWebResponse rsp = null;
    try
    {
        rsp = (HttpWebResponse)req.GetResponse();
        if (HttpStatusCode.OK == rsp.StatusCode)
        {
            Stream rspStream = rsp.GetResponseStream();     // 响应内容字节流
            using (StreamReader sr = new StreamReader(rspStream,Encoding.UTF8))
            {
                return sr.ReadToEnd();
            }
        }

    }
    finally
    {
        rsp.Close();
    }
    return null;
}

private static bool remoteCertificateValidate(object sender, X509Certificate cert, X509Chain chain, SslPolicyErrors error)
{
    return true;
}