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==))
{
StringBuilder buffer = new StringBuilder();
int i = ;
foreach (string key in parameters.Keys)
{
if (i > )
{
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, , 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", "");
parameters.Add("username", userName);
parameters.Add("password", password);
parameters.Add("mem_pass", "");
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。