Come estrarre Atom / RSS

Question

Dato un URL, se ha tutti i nodi RSS, quindi sto aggiungendo al database.

per esempio:.

questo URL , rssDoc.SelectNodes("rss/channel/item").Count è maggiore di zero.

l'url atomo , rssDoc.SelectNodes("rss/channel/item").count è uguale a zero.

Come posso verificare se l'URL Atom / RSS ha nodi o no? Ho cercato per rssDoc.SelectNodes("feed/entry").Count, ma mi sta dando conteggio zero.

Public Shared Function HasRssItems(ByVal url as string) As Boolean
Dim myRequest As WebRequest
Dim myResponse As WebResponse
Try
    myRequest = System.Net.WebRequest.Create(url)
    myRequest.Timeout = 5000
    myResponse = myRequest.GetResponse()

    Dim rssStream As Stream = myResponse.GetResponseStream()
    Dim rssDoc As New XmlDocument()
    rssDoc.Load(rssStream)

    Return rssDoc.SelectNodes("rss/channel/item").Count > 0
Catch ex As Exception
    Return False
Finally
    myResponse.Close()
End Try

End Function

Answer 1

Il problema principale è che l'XML "percorso del nodo" su questa linea:

Return rssDoc.SelectNodes("rss/channel/item").Count > 0

è valido solo per feed RSS , non ATOM feed .

Un modo che ho su questo in passato è quello di utilizzare una semplice funzione per convertire un feed ATOM in un feed RSS. Naturalmente, si potrebbe andare nella direzione opposta, o no la conversione a tutti, però, la conversione in un unico formato consente di scrivere un pezzo "generico" di codice che tirerà fuori i vari elementi di elementi di un feed che si può essere interessati in (cioè data, titolo, ecc.)

C'è un ATOM a RSS Converter articolo sul codice del progetto che fornisce una tale conversione, però, che si trova in C #. Ho convertito in precedenza manualmente questo a VB.NET me stesso, quindi ecco la versione VB.NET:

Private Function AtomToRssConverter(ByVal atomDoc As XmlDocument) As XmlDocument
    Dim xmlDoc As XmlDocument = atomDoc
    Dim xmlNode As XmlNode = Nothing
    Dim mgr As New XmlNamespaceManager(xmlDoc.NameTable)
    mgr.AddNamespace("atom", "http://purl.org/atom/ns#")
    Const rssVersion As String = "2.0"
    Const rssLanguage As String = "en-US"
    Dim rssGenerator As String = "RDFFeedConverter"
    Dim memoryStream As New MemoryStream()
    Dim xmlWriter As New XmlTextWriter(memoryStream, Nothing)
    xmlWriter.Formatting = Formatting.Indented
    Dim feedTitle As String = ""
    Dim feedLink As String = ""
    Dim rssDescription As String = ""

    xmlNode = xmlDoc.SelectSingleNode("//atom:title", mgr)
    If xmlNode Is Nothing Then
          This looks like an ATOM v1.0 format, rather than ATOM v0.3.
        mgr.RemoveNamespace("atom", "http://purl.org/atom/ns#")
        mgr.AddNamespace("atom", "http://www.w3.org/2005/Atom")
    End If

    xmlNode = xmlDoc.SelectSingleNode("//atom:title", mgr)
    If Not xmlNode Is Nothing Then
        feedTitle = xmlNode.InnerText
    End If
    xmlNode = xmlDoc.SelectNodes("//atom:link/@href", mgr)(2)
    If Not xmlNode Is Nothing Then
        feedLink = xmlNode.InnerText
    End If
    xmlNode = xmlDoc.SelectSingleNode("//atom:tagline", mgr)
    If Not xmlNode Is Nothing Then
        rssDescription = xmlNode.InnerText
    End If
    xmlNode = xmlDoc.SelectSingleNode("//atom:subtitle", mgr)
    If Not xmlNode Is Nothing Then
        rssDescription = xmlNode.InnerText
    End If

    xmlWriter.WriteStartElement("rss")
    xmlWriter.WriteAttributeString("version", rssVersion)
    xmlWriter.WriteStartElement("channel")
    xmlWriter.WriteElementString("title", feedTitle)
    xmlWriter.WriteElementString("link", feedLink)
    xmlWriter.WriteElementString("description", rssDescription)
    xmlWriter.WriteElementString("language", rssLanguage)
    xmlWriter.WriteElementString("generator", rssGenerator)
    Dim items As XmlNodeList = xmlDoc.SelectNodes("//atom:entry", mgr)
    If items Is Nothing Then
        Throw New FormatException("Atom feed is not in expected format. ")
    Else
        Dim title As String = [String].Empty
        Dim link As String = [String].Empty
        Dim description As String = [String].Empty
        Dim author As String = [String].Empty
        Dim pubDate As String = [String].Empty
        For i As Integer = 0 To items.Count - 1
            Dim nodTitle As XmlNode = items(i)
            xmlNode = nodTitle.SelectSingleNode("atom:title", mgr)
            If Not xmlNode Is Nothing Then
                title = xmlNode.InnerText
            End If
            Try
                link = items(i).SelectSingleNode("atom:link[@rel= alternate ]", mgr).Attributes("href").InnerText
            Catch ex As Exception
                link = items(i).SelectSingleNode("atom:link", mgr).Attributes("href").InnerText
            End Try
            xmlNode = items(i).SelectSingleNode("atom:content", mgr)
            If Not xmlNode Is Nothing Then
                description = xmlNode.InnerText
            End If
            xmlNode = items(i).SelectSingleNode("//atom:name", mgr)
            If Not xmlNode Is Nothing Then
                author = xmlNode.InnerText
            End If
            xmlNode = items(i).SelectSingleNode("atom:issued", mgr)
            If Not xmlNode Is Nothing Then
                pubDate = xmlNode.InnerText
            End If
            xmlNode = items(i).SelectSingleNode("atom:updated", mgr)
            If Not xmlNode Is Nothing Then
                pubDate = xmlNode.InnerText
            End If
            xmlWriter.WriteStartElement("item")
            xmlWriter.WriteElementString("title", title)
            xmlWriter.WriteElementString("link", link)
            If pubDate.Length < 1 Then
                pubDate = Date.MinValue.ToString()
            End If
            xmlWriter.WriteElementString("pubDate", Convert.ToDateTime(pubDate).ToUniversalTime().ToString("ddd, dd MMM yyyy HH:mm:ss G\MT"))
            xmlWriter.WriteElementString("author", author)
            xmlWriter.WriteElementString("description", description)
            xmlWriter.WriteEndElement()
        Next
        xmlWriter.WriteEndElement()
        xmlWriter.Flush()
        xmlWriter.Close()
    End If
    Dim retDoc As New XmlDocument()
    Dim outStr As String = Encoding.UTF8.GetString(memoryStream.ToArray())
    retDoc.LoadXml(outStr)
    Return retDoc
End Function

L'uso è abbastanza semplice. Basta caricare nel tuo feed ATOM in un oggetto XmlDocument e passarlo a questa funzione, e si otterrà un oggetto XmlDocument indietro, in formato RSS!

Se siete interessati, ho messo un intero RSSReader classe su pastebin.com