C# HttpWebRequest GET HTTP HTTPS 请求
下面是我编写的一个辅助类，在这个类中采用了HttpWebRequest中发送GET/HTTP/HTTPS请求，因为有的时候需要获取认证信息（如Cookie），所以返回的是HttpWebResponse对象，有了返回的HttpWebResponse实例，可以获取登录过程中返回的会话信息，也可以获取响应流。
using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Net.Security; using System.Security.Cryptography.X509Certificates; using System.DirectoryServices.Protocols; using System.ServiceModel.Security; using System.Net; using System.IO; using System.IO.Compression; using System.Text.RegularExpressions; namespace BaiduCang { /// <summary> /// 有关HTTP请求的辅助类 /// </summary> public class HttpWebResponseUtility { private static readonly string DefaultUserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)"; /// <summary> /// 创建GET方式的HTTP请求 /// </summary> /// <param name="url">请求的URL</param> /// <param name="timeout">请求的超时时间</param> /// <param name="userAgent">请求的客户端浏览器信息，可以为空</param> /// <param name="cookies">随同HTTP请求发送的Cookie信息，如果不需要身份验证可以为空</param> /// <returns></returns> public static HttpWebResponse CreateGetHttpResponse(string url,int? timeout, string userAgent,CookieCollection cookies) { if (string.IsNullOrEmpty(url)) { throw new ArgumentNullException("url"); } HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest; request.Method = "GET"; request.UserAgent = DefaultUserAgent; if (!string.IsNullOrEmpty(userAgent)) { request.UserAgent = userAgent; } if (timeout.HasValue) { request.Timeout = timeout.Value; } if (cookies != null) { request.CookieContainer = new CookieContainer(); request.CookieContainer.Add(cookies); } return request.GetResponse() as HttpWebResponse; } /// <summary> /// 创建POST方式的HTTP请求 /// </summary> /// <param name="url">请求的URL</param> /// <param name="parameters">随同请求POST的参数名称及参数值字典</param> /// <param name="timeout">请求的超时时间</param> /// <param name="userAgent">请求的客户端浏览器信息，可以为空</param> /// <param name="requestEncoding">发送HTTP请求时所用的编码</param> /// <param name="cookies">随同HTTP请求发送的Cookie信息，如果不需要身份验证可以为空</param> /// <returns></returns> public static HttpWebResponse CreatePostHttpResponse(string url,IDictionary<string,string> parameters,int? timeout, string userAgent,Encoding requestEncoding,CookieCollection cookies) { if (string.IsNullOrEmpty(url)) { throw new ArgumentNullException("url"); } if(requestEncoding==null) { throw new ArgumentNullException("requestEncoding"); } HttpWebRequest request=null; //如果是发送HTTPS请求 if(url.StartsWith("https",StringComparison.OrdinalIgnoreCase)) { ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult); request = WebRequest.Create(url) as HttpWebRequest; request.ProtocolVersion=HttpVersion.Version10; } else { request = WebRequest.Create(url) as HttpWebRequest; } request.Method = "POST"; request.ContentType = "application/x-www-form-urlencoded"; if (!string.IsNullOrEmpty(userAgent)) { request.UserAgent = userAgent; } else { request.UserAgent = DefaultUserAgent; } if (timeout.HasValue) { request.Timeout = timeout.Value; } if (cookies != null) { request.CookieContainer = new CookieContainer(); request.CookieContainer.Add(cookies); } //如果需要POST数据 if(!(parameters==null||parameters.Count==0)) { StringBuilder buffer = new StringBuilder(); int i = 0; foreach (string key in parameters.Keys) { if (i > 0) { buffer.AppendFormat("&{0}={1}", key, parameters[key]); } else { buffer.AppendFormat("{0}={1}", key, parameters[key]); } i++; } byte[] data = requestEncoding.GetBytes(buffer.ToString()); using (Stream stream = request.GetRequestStream()) { stream.Write(data, 0, data.Length); } } return request.GetResponse() as HttpWebResponse; } private static bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors) { return true; //总是接受 } } }
从上面的代码中可以看出POST数据到HTTP和HTTPS站点不同，POST数据到HTTPS站点的时候需要设置ServicePointManager类的ServerCertificateValidationCallback属性，并且在POST到https://passport.baidu.com/?login时还需要将HttpWebResquest实例的ProtocolVersion属性设置为HttpVersion.Version10（这个未验证是否所有的HTTPS站点都需要设置），否则在调用GetResponse()方法时会抛出“基础连接已经关闭: 连接被意外关闭。”的异常。
用法举例
这个类用起来也很简单：
（1）POST数据到HTTPS站点，用它来登录百度：
string loginUrl = "https://passport.baidu.com/?login"; string userName = "userName"; string password = "password"; string tagUrl = "http://cang.baidu.com/"+userName+"/tags"; Encoding encoding = Encoding.GetEncoding("gb2312"); IDictionary<string, string> parameters = new Dictionary<string, string>(); parameters.Add("tpl", "fa"); parameters.Add("tpl_reg", "fa"); parameters.Add("u", tagUrl); parameters.Add("psp_tt", "0"); parameters.Add("username", userName); parameters.Add("password", password); parameters.Add("mem_pass", "1"); HttpWebResponse response = HttpWebResponseUtility.CreatePostHttpResponse(loginUrl, parameters, null, null, encoding, null); string cookieString = response.Headers["Set-Cookie"];
（2）发送GET请求到HTTP站点
在cookieString中包含了服务器端返回的会话信息数据，从中提取了之后可以设置Cookie下次登录时带上这个Cookie就可以以认证用户的信息，假设我们已经登录成功并且获取了Cookie，那么发送GET请求的代码如下：
string userName = "userName"; string tagUrl = "http://cang.baidu.com/"+userName+"/tags"; CookieCollection cookies = new CookieCollection();//如何从response.Headers["Set-Cookie"];中获取并设置CookieCollection的代码略 response = HttpWebResponseUtility.CreateGetHttpResponse(tagUrl, null, null, cookies);
(3)发送POST请求到HTTP站点
以登录51CTO为例：
string loginUrl = "http://home.51cto.com/index.php?s=/Index/doLogin"; string userName = "userName"; string password = "password"; IDictionary<string, string> parameters = new Dictionary<string, string>(); parameters.Add("email", userName); parameters.Add("passwd", password); HttpWebResponse response = HttpWebResponseUtility.CreatePostHttpResponse(loginUrl, parameters, null, null, Encoding.UTF8, null);
在这里说句题外话，CSDN的登录处理是由http://passport.csdn.net/ajax/accounthandler.ashx这个Handler来处理的。
总结
在本文只是讲解了在C#中发送请求到HTTP和HTTPS的用法，分GET/POST两种方式，为减少一些繁琐和机械的编码，周公将其封装为一个类，发送数据之后返回HttpWebResponse对象实例，利用这个实例我们可以获取服务器端返回的Cookie以便用认证用户的身份继续发送请求，或者读取服务器端响应的内容，不过在读取响应内容时要注意响应格式和编码，本来在这个类中还有读取HTML和WML内容的方法（包括服务器使用压缩方式传输的数据），但限于篇幅和其它方面的原因，此处省略掉了。如有机会，在以后的文章中会继续讲述这方面的内容。
