Question

I’m trying to determine whether a given feed is Atom based or RSS based.

Here’s my code:

public boolean isRSS(String URL) throws ParserConfigurationException, SAXException, IOException{
        DocumentBuilder builder = DocumentBuilderFactory.newInstance()
                .newDocumentBuilder();
        Document doc = builder
                .parse(URL);
        return doc.getDocumentElement().getNodeName().equalsIgnoreCase() == "rss";
    }

Is there a better way to do it? would it be better if I used a SAX Parser instead?

Answer 1

Sniffing content is one method. But note that atom uses namespaces, and you are creating a non namespace aware parser.

public boolean isAtom(String URL) throws ParserConfigurationException, SAXException, IOException{
    DocumentBuilderFactory f = DocumentBuilderFActory.newInstance();
    f.setNamespaceAware(true);
    DocumentBuilder builder = f.newInstance().newDocumentBuilder();
    Document doc = builder.parse(URL);
    Element e = doc.getDocumentElement(); 
    return e.getLocalName().equals("feed") && 
            e.getNamespaceURI().equals("http://www.w3.org/2005/Atom");
}

Note also that you cannot compare using equalsIgnorCase(), since XML element names are case sensitive.

Another method is to react on the Content-Type header, if it is available in a HTTP GET request. Content-Type for ATOM would be application/atom+xml and for RSS application/rss+xml. I would suspect though, that not all RSS feed can be trusted to correctky set this header.

A third option is to look at the URL suffix, e.g. .atom and .rss.

The last two methods are easily configurable if you are using Spring or JAX-RS