解决：

使用asp.net中的httprequest和httpresponse来实现。

要点：

1。 通过附加一个cookiecontainer到httprequest对象中，可以得到登录后返回的代表SESSION ID的COOKIE。 见Login方法
2。 将此COOKIE包含在一个cookiecontainer中并附加到另一个HTTPREQUEST请求中，则可以实现SESSION的还原。见getPage方法

源程序如下：

getHttpInfo.aspx:
复制ASPX代码保存代码<%@ Page Language="c#" Codebehind="getHttpInfo.aspx.cs" AutoEventWireup="false" Inherits="PdfTest.getHttpInfo" %>

getHttpInfo.aspx.cs:
复制C#代码保存代码using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
//using System.Data.OleDb;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Net;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;
using Microsoft.Data.Odbc;

namespace PdfTest
{
///

private void Page_Load(object sender, System.EventArgs e)
{
// Put user code to initialize the page here

string strResult;

if (HttpContext.Current.Application["cookieheader"] != null)
{
cookieheader = (string) HttpContext.Current.Application["cookieheader"];
}
else
{
//Login into the website and keep the cookie for the session in the application variable
string strLogin = Login("http://www.thesiteyouwanttovisit/theloginpage.asp", "Action=&USERID=&Password=");
}

strResult = getPage("http://www.thesiteyouwanttovisit/theloginpage.asp", "Action=&data=");

//Write the result to htm file
FileStream htmFile = new FileStream(@"c:\save.htm", FileMode.OpenOrCreate);
StreamWriter sw = new StreamWriter(htmFile);
sw.Write(strResult);
sw.Close();
htmFile.Close();

// output the result
Response.Write(strResult);
}

public static string Login(String url, String paramList)
{
HttpWebResponse res = null;
string strResult = "";

try
{

HttpWebRequest req = (HttpWebRequest) WebRequest.Create(url);
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
req.AllowAutoRedirect = false;
CookieContainer cookieCon = new CookieContainer();
req.CookieContainer = cookieCon;

StringBuilder UrlEncoded = new StringBuilder();
Char[] reserved = { '?', '=', '&' };
byte[] SomeBytes = null;

if (paramList != null)
{
int i = 0, j;
while (i < paramList.Length)
{
j = paramList.IndexOfAny(reserved, i);
if (j == -1)
{
UrlEncoded.Append(HttpUtility.UrlEncode(paramList.Substring(i, paramList.Length - i)));
break;
}
UrlEncoded.Append(HttpUtility.UrlEncode(paramList.Substring(i, j - i)));
UrlEncoded.Append(paramList.Substring(j, 1));
i = j + 1;
}
SomeBytes = Encoding.UTF8.GetBytes(UrlEncoded.ToString());
req.ContentLength = SomeBytes.Length;
Stream newStream = req.GetRequestStream();
newStream.Write(SomeBytes, 0, SomeBytes.Length);
newStream.Close();
}
else
{
req.ContentLength = 0;
}

res = (HttpWebResponse) req.GetResponse();
cookieheader = req.CookieContainer.GetCookieHeader(new Uri(url));
HttpContext.Current.Application.Lock();
HttpContext.Current.Application["cookieheader"] = cookieheader;
HttpContext.Current.Application.UnLock();

Stream ReceiveStream = res.GetResponseStream();
Encoding encode = System.Text.Encoding.GetEncoding("utf-8");
StreamReader sr = new StreamReader(ReceiveStream, encode);
Char[] read = new Char[256];
int count = sr.Read(read, 0, 256);
while (count > 0)
{
String str = new String(read, 0, count);
strResult += str;
count = sr.Read(read, 0, 256);
}
}
catch (Exception e)
{
strResult = e.ToString();
}
finally
{
if (res != null)
{
res.Close();
}
}

return strResult;
}

public static string getPage(String url, String paramList)
{
HttpWebResponse res = null;
string strResult = "";

try
{

HttpWebRequest req = (HttpWebRequest) WebRequest.Create(url);
req.Method = "POST";
req.KeepAlive = true;
req.ContentType = "application/x-www-form-urlencoded";
CookieContainer cookieCon = new CookieContainer();
req.CookieContainer = cookieCon;
req.CookieContainer.SetCookies(new Uri(url), cookieheader);
StringBuilder UrlEncoded = new StringBuilder();
Char[] reserved = { '?', '=', '&' };
byte[] SomeBytes = null;

if (paramList != null)
{
int i = 0, j;
while (i < paramList.Length)
{
j = paramList.IndexOfAny(reserved, i);
if (j == -1)
{
UrlEncoded.Append(HttpUtility.UrlEncode(paramList.Substring(i, paramList.Length - i)));
break;
}
UrlEncoded.Append(HttpUtility.UrlEncode(paramList.Substring(i, j - i)));
UrlEncoded.Append(paramList.Substring(j, 1));
i = j + 1;
}
SomeBytes = Encoding.UTF8.GetBytes(UrlEncoded.ToString());
req.ContentLength = SomeBytes.Length;
Stream newStream = req.GetRequestStream();
newStream.Write(SomeBytes, 0, SomeBytes.Length);
newStream.Close();
}
else
{
req.ContentLength = 0;
}

res = (HttpWebResponse) req.GetResponse();
Stream ReceiveStream = res.GetResponseStream();
Encoding encode = System.Text.Encoding.GetEncoding("utf-8");
StreamReader sr = new StreamReader(ReceiveStream, encode);
Char[] read = new Char[256];
int count = sr.Read(read, 0, 256);
while (count > 0)
{
String str = new String(read, 0, count);
strResult += str;
count = sr.Read(read, 0, 256);
}
}
catch (Exception e)
{
strResult = e.ToString();
}
finally
{
if (res != null)
{
res.Close();
}
}

return strResult;
}

#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: This call is required by the ASP.NET Web Form Designer.
//
InitializeComponent();
base.OnInit(e);
}

///

}
#endregion

}
}