One of the major ways that spammers get email addresses is by crawling Web pages and extracting any email addresses they find. As part of your own Web site development, it’s a good idea to check your own Web pages to make sure you didn’t accidentally include any email addresses. Here’s a little VB.NET utility that can scan a Web page and extract most email addresses.
Private Sub cmdScan_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles cmdScan.Click ScanAPage(txtURL.Text)End Sub
The Regex Regular Expression class does the scanning. This particular pattern breaks down as follows:
w+ One or more characters, numbers or underscores@ The @ symbolw+ One or more characters, numbers or underscores( A group consisting of.. A period followed byw+ One or more characters, numbers or underscores) End of the groupPrivate m_EmailRE As New Regex("w+@(w+)(.w+)+")
Now, this expression is not perfect?it will detect some invalid email addresses, but keep in mind what it is designed for. This application isn’t a tool for spammers to extract email addresses?it’s a tool to help you spot email addresses you’ve inadvertently left in your code. So false positives aren’t harmful. The AddToList function checks for duplicates before listing the email addresses:
Private Sub AddToList(ByVal s As String) If Not ListBox1.Items.Contains(s.ToLower) Then ListBox1.Items.Add(s.ToLower) End IfEnd Sub
The ScanAPage function does the real work. It uses the WebRequest object to retrieve the specified Web page, then applies the Regular Expression to extract all patterns that match the email address, and adds them to the list:
Private Sub ScanAPage(ByVal url As String) Dim req As WebRequest req = WebRequest.Create(url) Dim pageinfo As String Dim response As WebResponse Dim thisuri As New Uri(url) Try response = req.GetResponse() Catch ex As Exception Exit Sub End Try Dim sr As New IO.StreamReader(response.GetResponseStream) pageinfo = sr.ReadToEnd() response.Close() Dim reresults As MatchCollection Dim onematch As Match ' Get Email addresses and add to list reresults = m_EmailRE.Matches(pageinfo) If Not reresults Is Nothing Then For Each onematch In reresults AddToList(onematch.Value) Next End IfEnd Sub
Dan Appleman is the president of Desaware, Inc. and the author of a number of programming books.