什么是Httphelper？
httpelpers是一个封装好拿来获取网络上资源的工具类。因为是用http协议，故取名httphelper。
httphelper出现的背景
使用WebClient可以很方便获取网络上的资源，例如
WebClient client = new WebClient(); string html= client.DownloadString("https://www.baidu.com/");
这样就可以拿到百度首页的的源代码，由于WebClient封装性太强，有时候不大灵活，需要对底层有更细致的把控，这个时候就需要打造自己的网络资源获取工具了；
HttpHelper初级
现在着手打造自己的下载工具，刚开始时候长这样
public class HttpHelp { public static string DownLoadString(string url) {
string Source = string.Empty;
HttpWebRequest request= (HttpWebRequest)WebRequest.Create(url);
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
using (Stream stream = response.GetResponseStream())
{
using (StreamReader reader = new StreamReader(stream, Encoding.UTF8))
{
Source = reader.ReadToEnd();
}
}
}
return Source;
}
}
程序总会出现各种异常的，这个时候加个Try catch语句
public class HttpHelp { public static string DownLoadString(string url) { string Source = string.Empty; try{ HttpWebRequest request= (HttpWebRequest)WebRequest.Create(url); using (HttpWebResponse response = (HttpWebResponse)request.GetResponse()) { using (Stream stream = response.GetResponseStream()) { using (StreamReader reader = new StreamReader(stream, Encoding.UTF8)) { Source = reader.ReadToEnd(); } } } } catch
{ Console.WriteLine("出错了，请求的URL为{0}", url); } return Source; } }
public static async Task<string> DownLoadString(string url) { return await Task<string>.Run(() => { string Source = string.Empty; try { HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url); using (HttpWebResponse response = (HttpWebResponse)request.GetResponse()) { using (Stream stream = response.GetResponseStream()) { using (StreamReader reader = new StreamReader(stream, Encoding.UTF8)) { Source = reader.ReadToEnd(); } } } } catch { Console.WriteLine("出错了，请求的URL为{0}", url); } return Source; }); }
HttpHelper完善
为了欺骗服务器，让服务器认为这个请求是浏览器发出的
request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:49.0) Gecko/20100101 Firefox/49.0";
有些资源是需要权限的，这个时候要伪装成某个用户，http协议是无状态的，标记信息都在cookie上面，给请求加上cookie
request.Headers.Add("Cookie", "这里填cookie，从浏览器上面拷贝")
再完善下，设定个超时吧
request.Timeout = 5000;
有些网站提供资源是GZIP压缩，这样可以节省带宽，所以请求头再加个
public static string DownLoadString(string url)
{
string Source = string.Empty;
try{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url); request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:49.0) Gecko/20100101 Firefox/49.0"; request.Headers.Add("Cookie", "这里是Cookie"); request.Headers.Add("Accept-Encoding", " gzip, deflate, br"); request.KeepAlive = true;//启用长连接 using (HttpWebResponse response = (HttpWebResponse)request.GetResponse()) { using (Stream dataStream = response.GetResponseStream()) { if (response.ContentEncoding.ToLower().Contains("gzip"))//解压 { using (GZipStream stream = new GZipStream(response.GetResponseStream(), CompressionMode.Decompress)) { using (StreamReader reader = new StreamReader(stream, Encoding.UTF8)) { Source = reader.ReadToEnd(); } } } else if (response.ContentEncoding.ToLower().Contains("deflate"))//解压 { using (DeflateStream stream = new DeflateStream(response.GetResponseStream(), CompressionMode.Decompress)) { using (StreamReader reader = new StreamReader(stream, Encoding.UTF8)) { Source = reader.ReadToEnd(); } } } else { using (Stream stream = response.GetResponseStream())//原始 { using (StreamReader reader = new StreamReader(stream, Encoding.UTF8)) { Source = reader.ReadToEnd(); } } } } } request.Abort(); } catch { Console.WriteLine("出错了，请求的URL为{0}", url); } return Source;
}
请求态度会被服务器拒绝，返回429。这个时候需要设置代理，我们的请求会提交到代理服务器，代理服务器会向目标服务器请求，得到的响应由代理服务器返回给我们。只要不断切换代理，服务器不会因为请求太频繁而拒绝掉程序的请求
var proxy = new WebProxy(“Adress”,8080);//后面是端口号 request.Proxy = proxy;//为httpwebrequest设置代理
至于如何获取代理，请见后面的博客
原文：http://www.cnblogs.com/zuin/p/6257125.html