基于C#实现网络爬虫 C#抓取网页Html源码

private void Search(string url){ string rl; WebRequest Request = WebRequest.Create(url.Trim());  WebResponse Response = Request.GetResponse();  Stream resStream = Response.GetResponseStream();  StreamReader sr = new StreamReader(resStream, Encoding.Default); StringBuilder sb = new StringBuilder(); while ((rl = sr.ReadLine()) != null) {  sb.Append(rl); }   string str = sb.ToString().ToLower();  string str_get = mid(str, "<ul class=/"post_list/">", "</ul>");   int start = 0; while (true) {  if (str_get == null)   break;  string strResult = mid(str_get, "href=/"", "/"", out start);  if (strResult == null)   break;  else  {   lab[url] += strResult;   str_get = str_get.Substring(start);  } }}    private string mid(string istr, string startString, string endString){ int iBodyStart = istr.IndexOf(startString, 0);    //开始位置 if (iBodyStart == -1)  return null; iBodyStart += startString.Length;       //第一次字符位置起的长度 int iBodyEnd = istr.IndexOf(endString, iBodyStart);   //第二次字符在第一次字符位置起的首次位置 if (iBodyEnd == -1)  return null; iBodyEnd += endString.Length;        //第二次字符位置起的长度 string strResult = istr.Substring(iBodyStart, iBodyEnd - iBodyStart - 1); return strResult;}  private string mid(string istr, string startString, string endString, out int iBodyEnd){ //初始化out参数,否则不能return iBodyEnd = 0;  int iBodyStart = istr.IndexOf(startString, 0);    //开始位置 if (iBodyStart == -1)  return null; iBodyStart += startString.Length;       //第一次字符位置起的长度 iBodyEnd = istr.IndexOf(endString, iBodyStart);   //第二次字符在第一次字符位置起的首次位置 if (iBodyEnd == -1)  return null; iBodyEnd += endString.Length;        //第二次字符位置起的长度 string strResult = istr.Substring(iBodyStart, iBodyEnd - iBodyStart - 1); return strResult;}