get base namespace from an OWL ontology

Question

Is there a way to get the base namespace from a OWL ontology file, without using DOM or similar, but just using Jena's API? Eg, from an OWL file:

<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:protege="http://protege.stanford.edu/plugins/owl/protege#"
    xmlns="http://www.owl-ontologies.com/Ontology1254827934.owl#"
    xmlns:xsp="http://www.owl-ontologies.com/2005/08/07/xsp.owl#"
    xmlns:owl="http://www.w3.org/2002/07/owl#"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
    xmlns:swrl="http://www.w3.org/2003/11/swrl#"
    xmlns:swrlb="http://www.w3.org/2003/11/swrlb#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
  xml:base="http://www.owl-ontologies.com/Ontology1254827934.owl">

how could I get http://www.owl-ontologies.com/Ontology1254827934.owl at runtime?

Answer 1

One way:

//Create the Ontology Model
OntModel model = ModelFactory.createOntologyModel();

//Read the ontology file
model.begin();
InputStream in = FileManager.get().open(FILENAME_HERE);
if (in == null) {
    throw new IllegalArgumentException("File: " + filename + " not found");
}        
model.read(in,"");
model.commit();

//Get the base namespace
model.getNsPrefixURI("");

Answer 2

Or if you really want the xml:base and not the empty xmlns:

final ArrayList<String> baseUriDropHere = new ArrayList<>();

DefaultHandler handler = new DefaultHandler() {

  @Override
  public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {

    if("rdf:RDF".equals(qName)) {
      for (int i=0; i<attributes.getLength(); i++) {
        if("xml:base".equals(attributes.getQName(i))) {
          baseUriDropHere.add(attributes.getValue(i));
          return;
        }
      }
    }
  }
};


try {

  SAXParserFactory factory = SAXParserFactory.newInstance();
  factory.setValidating(false);
  SAXParser parser = factory.newSAXParser();
  parser.parse(FILENAME_HERE, handler);

} catch (ParserConfigurationException e) {
} catch (SAXException e) {
} catch (IOException e) {
}

if(baseUriDropHere.isEmpty()) {
  System.out.println("no base uri set");
} else {
  System.out.println(baseUriDropHere.get(0));
}