asp.net需要登录后才能下载

using System;
using System.IO;
using System.Net;
using System.Web;

public class SRWebClient
{
CookieContainer cookie;
public SRWebClient()
{
cookie = new CookieContainer();
}

///
/// 下载Web源代码
///
public string DownloadHtml(string URL)
{
HttpWebRequest request = HttpWebRequest.Create(URL) as HttpWebRequest;
request.CookieContainer = cookie;
request.AllowAutoRedirect = false;

WebResponse res = request.GetResponse();
string r = "";

StreamReader S1 = new StreamReader(res.GetResponseStream(), System.Text.Encoding.Default);
try
{
r = S1.ReadToEnd();
}
catch (Exception er)
{
Log l = new Log();
l.writelog("下载Web错误", er.ToString());
}
finally
{
res.Close();
S1.Close();
}

return r;
}

///
/// 下载文件
///
public long DownloadFile(string FileURL, string FileSavePath)
{
long Filelength = 0;
HttpWebRequest req = HttpWebRequest.Create(FileURL) as HttpWebRequest;

req.CookieContainer = cookie;
req.AllowAutoRedirect = true;

HttpWebResponse res = req.GetResponse() as HttpWebResponse;
System.IO.Stream stream = res.GetResponseStream();
try
{
Filelength = res.ContentLength;

byte[] b = new byte[512];

int nReadSize = 0;
nReadSize = stream.Read(b, 0, 512);

System.IO.FileStream fs = System.IO.File.Create(FileSavePath);
try
{
while (nReadSize > 0)
{
fs.Write(b, 0, nReadSize);
nReadSize = stream.Read(b, 0, 512);
}
}
finally
{
fs.Close();
}
}
catch (Exception er)
{
Log l = new Log();
l.writelog("下载文件错误", er.ToString());
}
finally
{
res.Close();
stream.Close();
}

return Filelength;
}

///
/// 提交数据
///
public void Request(string RequestPageURL, RequestData Data)
{
string StrUrl = RequestPageURL;
HttpWebRequest request = HttpWebRequest.Create(StrUrl) as HttpWebRequest;
HttpWebResponse response;

string postdata = Data.GetData();
request.Referer = RequestPageURL;
request.AllowAutoRedirect = false;
request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.01; Windows NT 5.0)";
request.CookieContainer = cookie;

Uri u = new Uri(StrUrl);

if (postdata.Length > 0) //包含要提交的数据　就使用Post方式
{
//作为表单请求
request.ContentType = "application/x-www-form-urlencoded";
//方式就是Post
request.Method = "POST";

//把提交的数据换成字节数组
Byte[] B = System.Text.Encoding.Default.GetBytes(postdata);
request.ContentLength = B.Length;

Stream SW = request.GetRequestStream(); //开始提交数据
SW.Write(B, 0, B.Length);
SW.Close();
}

response = request.GetResponse() as HttpWebResponse;
response.Close();
}
}

using System.Collections;
using System.IO;

public class RequestData
{
ArrayList arr = new ArrayList();
public RequestData()
{

}

public string GetData()
{
string r = "";

for (int i = 0; i {
data d = (data) arr[i];
if (r.Length > 0)
r += "&";
r += d.Field + "=" + d.Value;
}
return r;
}

public void AddField(string Field, string Value)
{
data a = new data();
a.Field = Field;
a.Value = Value;

arr.Add(a);
}

struct data
{
public string Field, Value;
}
}