httpWebRequest獲取流和WebClient的文件抓取
昨天寫一個抓取，遇到了一個坑，就是在獲取網絡流的時候，人為的使用了stream.Length來獲取流的長度，獲取的時候會拋出錯誤，查了查文檔，原因是某些流是無法獲取到數據的長度的，所以不能直接得到。如果是常和stream打交道就能避免這個問題。其實直接使用do-while來獲取就行了，代碼如下：
int i=0; do { byte[] buffer = new byte[1024]; i = stream.Read(buffer, 0, 1024); fs.Write(buffer, 0, i); } while (i >0);其中while后只能寫i>0；而不能寫成i>=1024;原因可以看MSDN中的一段解釋：msdn
僅當流中沒有更多數據且預期不會有更多數據（如套接字已關閉或位於文件結尾）時，Read 才返回 0。 即使尚未到達流的末尾，實現仍可以隨意返回少於所請求的字節。
一下是httpwebrequest和webClient抓取數據的簡短代碼：
httpWebRequest
/// <summary> /// /// </summary> /// <param name="url">抓取url</param> /// <param name="filePath">保存文件名</param> /// <param name="oldurl">來源路徑</param> /// <returns></returns> public static bool HttpDown(string url, string filePath, string oldurl) { try { HttpWebRequest req = WebRequest.Create(url) as HttpWebRequest; req.Accept = @"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8 "; req.Referer = oldurl; req.UserAgent = @" Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.154 Safari/537.36 "; req.ContentType = "application/octet-stream"; HttpWebResponse response = req.GetResponse() as HttpWebResponse; Stream stream = response.GetResponseStream(); // StreamReader readStream=new StreamReader FileStream fs = File.Create(filePath); long length = response.ContentLength; int i=0; do { byte[] buffer = new byte[1024]; i = stream.Read(buffer, 0, 1024); fs.Write(buffer, 0, i); } while (i >0); fs.Close(); return true; } catch (Exception ex) { return false; } }WebClient
public static bool Down(string url, string desc,string oldurl) { try { WebClient wc = new WebClient(); wc.Headers.Add(HttpRequestHeader.Accept, @"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8 "); wc.Headers.Add(HttpRequestHeader.Referer, oldurl); wc.Headers.Add(HttpRequestHeader.UserAgent, @" Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.154 Safari/537.36 "); wc.Headers.Add(HttpRequestHeader.ContentType, "application/octet-stream"); wc.DownloadFile(new Uri(url), desc); Console.WriteLine(url); Console.WriteLine(" "+desc + " yes!"); return true; } catch (Exception ex) { return false; } }