输入一个地址，就可以把那个网页中的链接提取出来，下面这段代码可以轻松实现，主要的是用到了正则表达式。
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GetUrl.aspx代码如下：
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<%@ Page Language=”vb” CodeBehind=”GetUrl.aspx.vb” AutoEventWireup=”false” Inherits=”aspxWeb.GetUrl” %>
<html>
<head>
<META http-equiv=”content-type” content=”text/html; charset=gb2312″>
</head>
<body>
<form id=”Form1″ method=”post” runat=”server”>
<P>
<asp:Label id=”Label1″ runat=”server”></asp:Label>
<asp:TextBox id=”urlTextBox” runat=”server” Width=”336px”>
http://lucky_elove.www1.dotnetplayground.com/
</asp:TextBox>
<asp:Button onClick=”scrapeButton_Click” id=”scrapeButton” runat=”server”></asp:Button>
</P>
<HR width=”100%” SIZE=”1″>
<P>
<asp:Label id=”TipResult” runat=”server”></asp:Label>
<asp:TextBox id=”resultLabel” runat=”server” TextMode=”MultiLine”
Width=”100%” Height=”400″></asp:TextBox>
</P>
</form>
</body>
</html> 后代码GetUrl.aspx.vb如下：
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Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Text.RegularExpressions
Imports System
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Public Class GetUrl
Inherits System.Web.UI.Page
Protected WithEvents Label1 As System.Web.UI.WebControls.Label
Protected WithEvents urlTextBox As System.Web.UI.WebControls.TextBox
Protected WithEvents scrapeButton As System.Web.UI.WebControls.Button
Protected WithEvents TipResult As System.Web.UI.WebControls.Label
Protected WithEvents resultLabel As System.Web.UI.WebControls.TextBox
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#Region ” Web 窗体设计器生成的代码 “
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‘该调用是 Web 窗体设计器所必需的。
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
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End Sub
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Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
‘CODEGEN: 此方法调用是 Web 窗体设计器所必需的
‘不要使用代码编辑器修改它。
InitializeComponent()
End Sub
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#End Region
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Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
‘在此处放置初始化页的用户代码
Label1.Text = “请输入一个URL地址：”
scrapeButton.Text = “分离Href链接”
End Sub
Private report As New StringBuilder()
Private webPage As String
Private countOfMatches As Int32
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Public Sub scrapeButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
webPage = GrabUrl()
Dim myDelegate As New MatchEvaluator(AddressOf MatchHandler)
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Dim linksExpression As New Regex( _
“\\<a.+?href=[\'""](?!http\\:\\/\\/)(?!mailto\\:)(?>foundAnchor>[^\'"">]+?)[^>]*?\\>”, _
RegexOptions.Multiline Or RegexOptions.IgnoreCase Or RegexOptions.IgnorePatternWhitespace)
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Dim newWebPage As String = linksExpression.Replace(webPage, myDelegate)
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TipResult.Text = “<h2>从 ” & urlTextBox.Text & “分离出的Href链接</h2>” & _
“<b>找到并整理” & countOfMatches.ToString() & ” 个链接</b><br><br>” & _
report.ToString().Replace(Environment.NewLine, “<br>”)
TipResult.Text &= “<h2>整理过的页面</h2><script>window.document.title=’抓取网页中的链接’</script>”
resultLabel.Text = newWebPage
End Sub
Public Function MatchHandler(ByVal m As Match) As String
Dim link As String = m.Groups(“foundAnchor”).Value
Dim rToL As New Regex(“^”, RegexOptions.Multiline Or RegexOptions.RightToLeft)
Dim col, row As Int32
Dim lineBegin As Int32 = rToL.Match(webPage, m.Index).Index
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row = rToL.Matches(webPage, m.Index).Count
col = m.Index – lineBegin
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report.AppendFormat( _
“Link <b>{0}</b>, fixed at row: {1}, col: {2}{3}”, _
Server.HtmlEncode(m.Groups(0).Value), _
row, _
col, _
Environment.NewLine _
)
Dim newLink As String
If link.StartsWith(“/”) Then
newLink = link.Substring(1)
Else
newLink = link
End If
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countOfMatches += 1
Return m.Groups(0).Value.Replace(link, newLink)
End Function
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Private Function GrabUrl() As String
Dim wc As New WebClient()
Dim s As Stream = wc.OpenRead(urlTextBox.Text)
Dim sr As StreamReader = New StreamReader(s, System.Text.Encoding.Default)
GrabUrl = sr.ReadToEnd
s.Close()
wc.Dispose()
End Function
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End Class
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来源: 孟宪会之精彩世界