httpWebRequest获取流和WebClient的文件抓取

昨天写一个抓取，遇到了一个坑，就是在获取网络流的时候，人为的使用了stream.Length来获取流的长度，获取的时候会抛出错误，查了查文档，原因是某些流是无法获取到数据的长度的，所以不能直接得到。如果是常和stream打交道就能避免这个问题。其实直接使用do-while来获取就行了，代码如下：

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后只能写i>0；而不能写成i>=1024;原因可以看MSDN中的一段解释：msdn

仅当流中没有更多数据且预期不会有更多数据（如套接字已关闭或位于文件结尾）时，Read 才返回 0。 即使尚未到达流的末尾，实现仍可以随意返回少于所请求的字节。

一下是httpwebrequest和webClient抓取数据的简短代码：

httpWebRequest

/// <summary>
///
/// </summary>
/// <param name="url">抓取url</param>
/// <param name="filePath">保存文件名</param>
/// <param name="oldurl">来源路径</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;
    }

}