VB.NET

A Simple Web Crawler

See more Spider Examples

This demonstrates a very simple web crawler using the Chilkat Spider component. VB.NET

Dim success As Boolean = False

Dim spider As New Chilkat.Spider

Dim seenDomains As New Chilkat.StringArray
Dim seedUrls As New Chilkat.StringArray

seenDomains.Unique = True
seedUrls.Unique = True

' You will need to change the start URL to something else...
seedUrls.Append("http://something.whateverYouWant.com/")

' Set outbound URL exclude patterns
' URLs matching any of these patterns will not be added to the 
' collection of outbound links.
spider.AddAvoidOutboundLinkPattern("*?id=*")
spider.AddAvoidOutboundLinkPattern("*.mypages.*")
spider.AddAvoidOutboundLinkPattern("*.personal.*")
spider.AddAvoidOutboundLinkPattern("*.comcast.*")
spider.AddAvoidOutboundLinkPattern("*.aol.*")
spider.AddAvoidOutboundLinkPattern("*~*")

' Use a cache so we don't have to re-fetch URLs previously fetched.
spider.CacheDir = "c:/spiderCache/"
spider.FetchFromCache = True
spider.UpdateCache = True

While seedUrls.Count > 0

    Dim url As String = seedUrls.Pop()
    spider.Initialize(url)

    ' Spider 5 URLs of this domain.
    ' but first, save the base domain in seenDomains
    Dim domain As String = spider.GetUrlDomain(url)
    seenDomains.Append(spider.GetBaseDomain(domain))

    Dim i As Integer

    For i = 0 To 4
        success = spider.CrawlNext()
        If (success = True) Then

            ' Display the URL we just crawled.
            Debug.WriteLine(spider.LastUrl)

            ' If the last URL was retrieved from cache,
            ' we won't wait.  Otherwise we'll wait 1 second
            ' before fetching the next URL.
            If (spider.LastFromCache <> True) Then
                spider.SleepMs(1000)
            End If


        Else
            ' cause the loop to exit..
            i = 999
        End If


    Next

    ' Add the outbound links to seedUrls, except
    ' for the domains we've already seen.
    For i = 0 To spider.NumOutboundLinks - 1

        url = spider.GetOutboundLink(i)
        Dim domain As String = spider.GetUrlDomain(url)
        Dim baseDomain As String = spider.GetBaseDomain(domain)
        If (seenDomains.Contains(baseDomain) = False) Then
            ' Don't let our list of seedUrls grow too large.
            If (seedUrls.Count < 1000) Then
                seedUrls.Append(url)
            End If

        End If


    Next

End While