用来获取网页的类（转！vb.net参考）

Imports System.Net
Imports System.IO

Public Class HttpDriverClass HttpDriver

Public Function GetPage()Function GetPage(ByVal url As String, Optional ByRef postPara As String = "", Optional ByRef encType As String = "GB2312") As String
Return GetPage(url, postPara, Nothing, False, encType)
End Function

Public Function GetPage()Function GetPage(ByVal url As String, ByRef postPara As System.Collections.Hashtable, Optional ByRef encType As String = "GB2312") As String
Return GetPage(url, ColToStr(postPara), encType)
End Function

Public Function GetPage()Function GetPage(ByVal url As String, ByRef postPara As String, ByRef cookies As CookieCollection, ByVal hasCookie As Boolean, Optional ByRef encType As String = "GB2312", Optional ByRef refer As String = "") As String
If (url.StartsWith("http://") = False) Then
url = "http://" & url
End If
Dim hRqst As HttpWebRequest = HttpWebRequest.Create(url)
If (hasCookie = True AndAlso (Not cookies Is Nothing)) Then
hRqst.CookieContainer = New CookieContainer
hRqst.CookieContainer.Add(cookies)
End If

hRqst.ContentType = "application/x-www-form-urlencoded"
hRqst.Headers.Add("Accept-Language", "zh-cn")
Dim streamData As Stream
Dim bt() As Byte
If (postPara = "") Then
hRqst.Method = "GET"
Else
hRqst.Method = "POST"
hRqst.AllowWriteStreamBuffering = True
bt = System.Text.Encoding.ASCII.GetBytes(postPara)
hRqst.ContentLength = bt.Length
hRqst.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0)"
hRqst.Referer = refer
hRqst.KeepAlive = False
hRqst.Timeout = 20000
streamData = hRqst.GetRequestStream()
streamData.Write(bt, 0, bt.Length)
streamData.Close()
End If
Dim hRsp As HttpWebResponse
hRsp = hRqst.GetResponse()
streamData = hRsp.GetResponseStream()
If (hasCookie = True AndAlso (Not hRsp.Cookies Is Nothing)) Then
cookies.Add(hRsp.Cookies)
End If
If (encType = "") Then
encType = "GB2312"
End If
Dim readStream As New IO.StreamReader(streamData, System.Text.Encoding.GetEncoding(encType))
GetPage = readStream.ReadToEnd()
streamData.Close()
End Function

Public Function GetPage()Function GetPage(ByVal url As String, ByRef postPara As System.Collections.Hashtable, ByRef cookies As CookieCollection, ByVal hasCookie As Boolean, Optional ByRef encType As String = "GB2312") As String
Return GetPage(url, ColToStr(postPara), cookies, True, encType)
End Function

Public Function GetPage()Function GetPage(ByVal url As String, ByRef cookies As CookieCollection, ByVal hasCookie As Boolean, Optional ByRef encType As String = "GB2312") As String
Return GetPage(url, "", cookies, True, encType)
End Function

'该函数用于转换表单项集合为字符串
Public Shared Function ColToStr()Function ColToStr(ByRef ht As System.Collections.Hashtable, Optional ByRef encType As String = "GB2312") As String
Dim str As String
Dim para As DictionaryEntry
For Each para In ht
str &= System.Web.HttpUtility.UrlEncode(CType(para.Key, String), Text.Encoding.GetEncoding(encType))
str &= "="
str &= System.Web.HttpUtility.UrlEncode(CType(para.Value, String), Text.Encoding.GetEncoding(encType))
str &= "&"
Next
str = str.Substring(0, str.Length - 1)
Return str
End Function

End Class

如果需要支持cookie，并支持refer，可以通过下面这个类来使用上面的httpdriver。

'该类用于访问含有cookie的页面
Imports System.IO

Public Class UserAgentClass UserAgent
Private m_cookies As New System.Net.CookieCollection
Private refer As String
Private hd As New HttpDriver

Public Function GetPage()Function GetPage(ByVal url As String, Optional ByRef postPara As String = "", Optional ByRef encType As String = "GB2312") As String
GetPage = hd.GetPage(url, postPara, m_cookies, True, encType, refer)
refer = url
End Function

Public Function GetPage()Function GetPage(ByVal url As String, ByRef postPara As Hashtable, Optional ByRef encType As String = "GB2312") As String
Return GetPage(url, hd.ColToStr(postPara), encType)
End Function

Public Function SetCookie()Function SetCookie(ByVal cookies As System.Net.CookieCollection)
m_cookies = cookies
End Function

Public Function GetCookie()Function GetCookie() As System.Net.CookieCollection
Return m_cookies
End Function
End Class

轻量的get网页的函数
Public Function GetPage()Function GetPage(ByVal url As String) As String
Dim hRqst As HttpWebRequest = HttpWebRequest.Create(url)

hRqst.ContentType = "application/x-www-form-urlencoded"
hRqst.Method = "GET"
Dim streamData As Stream

Dim hRsp As HttpWebResponse = hRqst.GetResponse()
streamData = hRsp.GetResponseStream()

Dim readStream As New IO.StreamReader(streamData, System.Text.Encoding.GetEncoding("GB2312"))
GetPage = readStream.ReadToEnd()
streamData.Close()
End Function

Get方法：
Dim ua as New UserAgent
Dim content as String
Dim url as String
url = "www.sina.com.cn"
content = ua.GetPage(url)

Post方法：
Dim ua as New UserAgent
Dim content as String
Dim url as String
Dim ht as New HashTable

url = "mail.sina.com.cn"
ht.Add("username", "用户名")
ht.Add("password", "密码")
content = ua.GetPage(url, ht)