Trying to Remove Individual gives NullPointerException

Question

I try to remove an existing individual from my RDF file, but I always get a NullPointerException. The Individual I am getting is there, because I can print out a property. Can someone please tell me what I have done wrong?

final static String SN = "http://vaceta.pavo.uberspace.de/RDF/social-media.owl#";

InputStream in = context.getResourceAsStream("WEB-INF/resources/social-media.rdf");
OntModel model = ModelFactory.createOntologyModel(OntModelSpec.OWL_MEM);
model.read(in, null);
in.close();

Individual user01 = model.getIndividual(SN + "User01");
model.remove(user01, null, (RDFNode) null);
model.remove(null, null, user01);

output = new FileOutputStream(context.getRealPath("/")+"WEB-INF/resources/social-media.rdf");
model.writeAll(output, "RDF/XML", null);
output.close();

stacktrace:

enter image description here

You give 2 null references into a method and then you're suprised by an NPE? I think you should tell us why this should not lead to a NPE. — Bernd Ebertz, Apr 25 '14 at 13:57
Sorry I am new in Jena and it is very confusing to me. I learned, that the 3 arguments are like triples, but what should I enter, if I want to delete the entire individual? thank you — klanm, Apr 25 '14 at 14:03
@SirRotN In many of Jena's API methods, `null` is a used as wildcard in triples. E.g., `listStatements( x, null, null )` provides all triples whose subject is `x`; `remove( null, x, null )` would remove all triples whose predicate is `x`, and so on. — Joshua Taylor, Apr 25 '14 at 14:11
@vacetahanna You're on the right track. Sir RotN's comment is not terrible Java advice in general, but Jena's API *does* use `null` as a wildcard in triple patterns, so your use is sensible. — Joshua Taylor, Apr 25 '14 at 14:12
@JoshuaTaylor Suprising. As far as I can see the only implementation I fond looks like graph.delete( Triple.create( s.asNode(), p.asNode(), o.asNode() ) ); it calls asNode() on all the parameters. Sure that the wildcard thinking applies here. (Code might be old just the first I found) — Bernd Ebertz, Apr 25 '14 at 14:18
@SirRotN Yeah, the code here isn't right; I was just pointing out that it's not entirely mistaken. I think what OP wants here is [`removeAll(s,p,o)`](https://jena.apache.org/documentation/javadoc/jena/com/hp/hpl/jena/rdf/model/Model.html). — Joshua Taylor, Apr 25 '14 at 14:20

Joshua Taylor · Accepted Answer · 2014-04-25T14:27:32.130

You're using ModelCon.remove(s,p,o) which doesn't allow nulls. You want to use Model.removeAll(s,p,o) instead which does allow nulls and uses them as wildcards. Here are the corresponding Javadocs (with emphasis added):

ModelCon.remove
Model remove(Resource s, Property p, RDFNode o)
remove the statement (s, p, o) from this model and answer this model. None of s, p, o are permitted to be null: for wildcard removal, see removeAll.

Model.removeAll

Model removeAll(Resource s, Property p, RDFNode r)

Remove all the statements matching (s, p, o) from this model.

Trying to Remove Individual gives NullPointerException

1 Answers1

ModelCon.remove

Model.removeAll