我正在开发app，我需要在自动提供凭据后从网页捕获信息。一些我如何设法做自动登录和页面重定向。这是我的代码：
HttpWebRequest req = (HttpWebRequest)WebRequest.Create("https://abcd.com.au/categories/A_dfn/sdf");
HttpWebResponse res = req.GetResponse() as HttpWebResponse;
StringBuilder sb = new StringBuilder();
byte[] buf = new byte[10000];
Stream resStream = res.GetResponseStream();
string s = null;
int c = 0;
do
{
c = resStream.Read(buf, 0, buf.Length);
if (c != 0) {
s = ASCIIEncoding.ASCII.GetString(buf, 0, c);
sb.Append(s);
}
} while (c > 0);
string oldhead = "class=\"login_button\">";
string newhead = "class=\"login_button\"> <script type=\"text/javascript\">document.getElementById('btn').click()</script>";
sb.Replace(oldhead, newhead);
string oldbtn = "value=\"Submit\"";
string newbtn = "value=\"Submit\" id=\"btn\" ";
sb.Replace(oldbtn, newbtn);
string oldAction = "<form action=\"/login\" method=\"post\">";
string newAction = "<form action=\"https://abcd.com.au/login?orig_req_url=%2Fcategories/A_dfn/sdf\" method=\"post\">";
sb.Replace(oldAction, newAction);
string oldUsername = "<input id=\"login_email\" type=\"text\" name=\"user[email_address]\" class=\"textBox\" value=\"\">";
string newUserName = "<input id=\"login_email\" type=\"text\" name=\"user[email_address]\" class=\"textBox\" value=\"abc@xyz.com.au\">";
sb.Replace(oldUsername, newUserName);
string oldPass = "<input id=\"login_password\" type=\"password\" name=\"user[password]\" class=\"textBox\" value=\"\">";
string newPass = "<input id=\"login_password\" type=\"password\" name=\"user[password]\" class=\"textBox\" value=\"abc\">";
sb.Replace(oldPass,newPass);
Response.Write(sb);
这是通过渲染页面（Response.write（sb））显示我想要的预期输出。但是，现在我想做同样的事情，而不是重定向到“https://abcd.com.au/login?orig_req_url=%2Fcategories/A_dfn/sdf”，并希望在此做更多的事情。我希望在某个缓冲区中获得Response.Write（sb）的输出。有可能吗？
这是一个例子，它解释了我想要做的事情。 我正在寻找一个产品的数量名称：螺丝15毫米，这位于页面https://abcd.com.au/%2Fcategories/A_dfn/sdf。 所以，我首先请求此URL，但是需要登录才能访问该页面，它会将我重定向到登录页面，填写用户名和密码，使用javascript按下登录按钮，然后重定向到Originally Requested页面。在这个页面上，我想找到该产品，并将信息返回到我的网络应用程序。
我想做的所有这一切都没有向用户展示。 我只想显示检索到的信息。
感谢。
答案 0 :(得分：0)
您正在寻找的是一个持久的会话。您解决此问题的方法不正确。您正在客户端触发提交。您要实现的目标应该在服务器端完成。
您的方案的关键是坚持（存储）会话＆amp;登录页面设置的cookie;然后在您下一次请求产品信息之前，将凭证注入请求的webRequest。
如果不知道您尝试筛选的网站，则没有通用的方法。但一般步骤如上。基本上，您需要为此创建一个自定义类。
此外，您需要 HTMLAgilityPack 来解析HTML节点。这是正确的方法。
编辑：添加了我的代码。就是这样，我在前一段时间创建了这门课程。所以，你很幸运。但是，您需要安装HTMLAgilityPack＆amp;参考使用它。您可以在http://htmlagilitypack.codeplex.com/下载HAP。如果您想进行任何严肃的屏幕抓取，HAP是事实上的标准。
Public Class clsBrowserSession
'=================================================================================================================================
'This is a special Browser Post class
' Instead of just POST to a URL as per the clsWeb.fnsPostResponse()
' clsBrowserSession allows us to LOAD a page first, persist all the cookies and variables, and then only POST to the target URL.
' The reason is that some program will drop (lets say) a SessionID as an input when you first load the page.
' and when you post, without the SessionID (variable), it will reject the POST. Thus clsBrowserSession can solve this problem.
'=================================================================================================================================
' USAGE:
' Dim voBrowserSession As New clsBrowserSession
' voBrowserSession.sbLoadPage("https://xxx.yyy.net.my/publicncdenq/index.htm")
' voBrowserSession.proFormElements("UserID") = "myID"
' voBrowserSession.proFormElements("Password") = "myPassword"
' Dim vsResponseHTML As String = voBrowserSession.Post("https://xxx.yyy.net.my/publicncdenq/index.htm")
Private vbIsPostingInProgress As Boolean
Public voCookies As System.Net.CookieCollection
Public proHTMLDoc As HtmlAgilityPack.HtmlDocument
Public proFormElements As clsFormElementCollection
Public Sub sbLoadPage(pvsURL As String)
vbIsPostingInProgress = False
fnoCreateWebRequestObject().Load(pvsURL)
End Sub
Public Function Post(pvsURL As String) As String
vbIsPostingInProgress = True
fnoCreateWebRequestObject().Load(pvsURL, "POST")
Return proHTMLDoc.DocumentNode.InnerHtml
End Function
Private Function fnoCreateWebRequestObject() As HtmlAgilityPack.HtmlWeb
Dim voWeb As New HtmlAgilityPack.HtmlWeb
voWeb.UseCookies = True
voWeb.PreRequest = New HtmlAgilityPack.HtmlWeb.PreRequestHandler(AddressOf event_OnPreRequest)
voWeb.PostResponse = New HtmlAgilityPack.HtmlWeb.PostResponseHandler(AddressOf event_OnAfterResponse)
voWeb.PreHandleDocument = New HtmlAgilityPack.HtmlWeb.PreHandleDocumentHandler(AddressOf event_OnPreHandleDocument)
Return voWeb
End Function
Private Sub sbAddPostDataTo(pvoRequest As Net.HttpWebRequest)
Dim vsPayload As String = proFormElements.fnsAssemblePostPayload()
Dim vabyteBuffer As Byte() = Text.Encoding.UTF8.GetBytes(vsPayload.ToCharArray())
pvoRequest.ContentLength = vabyteBuffer.Length
pvoRequest.ContentType = "application/x-www-form-urlencoded"
pvoRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.97 Safari/537.11"
pvoRequest.GetRequestStream().Write(vabyteBuffer, 0, vabyteBuffer.Length)
End Sub
Private Sub sbAddvoCookiesTo(pvoRequest As Net.HttpWebRequest)
If (Not IsNothing(voCookies)) Then
If voCookies.Count > 0 Then pvoRequest.CookieContainer.Add(voCookies)
End If
End Sub
Private Sub sbSaveCookiesFrom(pvoResponse As Net.HttpWebResponse)
If pvoResponse.Cookies.Count > 0 Then
If IsNothing(voCookies) Then voCookies = New Net.CookieCollection
voCookies.Add(pvoResponse.Cookies)
End If
End Sub
Private Sub sbSaveHtmlDocument(pvoHTMLDocument As HtmlAgilityPack.HtmlDocument)
proHTMLDoc = pvoHTMLDocument
proFormElements = New clsFormElementCollection(proHTMLDoc)
End Sub
Protected Function event_OnPreRequest(pvoRequest As Net.HttpWebRequest) As Boolean
sbAddvoCookiesTo(pvoRequest)
If vbIsPostingInProgress Then sbAddPostDataTo(pvoRequest)
Return True
End Function
Protected Sub event_OnAfterResponse(pvoRequest As System.Net.HttpWebRequest, pvoResponse As Net.HttpWebResponse)
sbSaveCookiesFrom(pvoResponse)
End Sub
Protected Sub event_OnPreHandleDocument(pvoHTMLDocument As HtmlAgilityPack.HtmlDocument)
sbSaveHtmlDocument(pvoHTMLDocument)
End Sub
'-----------------------------------------------------------------------------------------------------
'Form Elements class
' Note: This element class will only capture (any) INPUT elements only, which should be enough
' for most cases. It can be easily modified to add other SELECT, TEXTAREA, etc voInputs
'-----------------------------------------------------------------------------------------------------
Public Class clsFormElementCollection
Inherits Dictionary(Of String, String)
Public Sub New(htmlDoc As HtmlAgilityPack.HtmlDocument)
Dim voInputs As Collections.Generic.IEnumerable(Of HtmlAgilityPack.HtmlNode) = htmlDoc.DocumentNode.Descendants("input")
For Each voInput As HtmlAgilityPack.HtmlNode In voInputs
Dim vsName = voInput.GetAttributeValue("name", "undefined")
Dim vsValue = voInput.GetAttributeValue("value", "")
If vsName <> "undefined" Then Add(vsName, vsValue)
Next
End Sub
Public Function fnsAssemblePostPayload() As String
Dim sb As New Text.StringBuilder
For Each voKeyValuePair In Me
Dim vsValue = System.Web.HttpUtility.UrlEncode(voKeyValuePair.Value)
sb.Append("&" & voKeyValuePair.Key & "=" & vsValue)
Next
Return sb.ToString.Substring(1)
End Function
End Class
End Class
将上述内容转换为类对象并实例化它。用法示例位于注释中。你想要vsResponseHTML字符串。