C# 加载 java 后下载网页

如何下载使用基于java的加载机制的网页？由于站点机制，下面的代码返回几乎为空的文档。在浏览器中查看时，您会看到"正在加载..."一段时间后，内容就会呈现。我也想避免使用Web浏览器控件。

HtmlDocument doc = new HtmlDocument();
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
            req.AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip;
if (!string.IsNullOrWhiteSpace(userAgent))
                req.UserAgent = userAgent;
if (cookies != null)
    {
        req.CookieContainer = new CookieContainer();
        foreach (Cookie c in cookies)
        req.CookieContainer.Add(c);
    }
var resp = req.GetResponse();
var resp_str = resp.GetResponseStream();
using (StreamReader sr = new StreamReader(resp_str, Encoding.GetEncoding("windows-1251")))
    {
        string r = sr.ReadToEnd();
        doc.LoadHtml(r);
    }
return doc;