Invalid XPath query - using jcabi on Java

Question

I'm finding an unexpected behavior with jcabi processing some data.

The data (just the beginning)

<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dcat="http://www.w3.org/ns/dcat#" xmlns:dct="http://purl.org/dc/terms/" xmlns:foaf="http://xmlns.com/foaf/0.1/" xmlns:owl="http://www.w3.org/2002/07/owl#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
  <dcat:Dataset rdf:about="http://about.html">
    <owl:sameAs rdf:resource="urn:uuid:123456789810" />
    <dct:description>SOME....</dct:description>
    <dcat:keyword>SOME....</dcat:keyword>
    <foaf:homepage rdf:resource="http://zzzzzzzzz" />
    <rdfs:label>SOME....</rdfs:label>
    <dct:identifier>SOME....</dct:identifier>
    <dct:title>SOME....</dct:title>
    <dcat:distribution>
      <dcat:Distribution>
        <dcat:accessURL rdf:resource="http://xxxxxxxxx" />
        <dct:title>Data 1</dct:title>
      </dcat:Distribution>
    </dcat:distribution>
    <dcat:distribution>
      <dcat:Distribution>
        <dcat:accessURL rdf:resource="http://yyyyyyyyy" />
        <dct:title>Data 2</dct:title>
      </dcat:Distribution>
    </dcat:distribution>
    <!-- ... -->
  </dcat:Dataset>
</rdf:RDF>

I try to get a list of dcat:distribution

The code:

XML xml = new XMLDocument(data);
List<XML> lista = xml.nodes("/rdf:RDF[1]/dcat:DataSet[1]/dcat:distribution");

And I get this error:

invalid XPath query '/rdf:RDF[1]/dcat:DataSet[1]/dcat:distribution' by com.sun.org.apache.xpath.internal.jaxp.XPathFactoryImpl

I try with:

/rdf:RDF/dcat:DataSet/dcat:distribution
//dcat:DataSet/dcat:distribution
//dcat:distribution
/rdf:RDF/dcat:DataSet
//dcat:DataSet

Any ideas?

Kind regards

Answer 1

When using jcabi-xml, you have to manually register all the namespaces that are used throughout your document.

Given your sample file, you might want to write something like this:

XML xml = new XMLDocument(data)
    .registerNs("owl",  "http://www.w3.org/2002/07/owl#")
    .registerNs("rdfs", "http://www.w3.org/2000/01/rdf-schema#")
    .registerNs("rdf",  "http://www.w3.org/1999/02/22-rdf-syntax-ns#")
    .registerNs("dcat", "http://www.w3.org/ns/dcat#")
    .registerNs("dct",  "http://purl.org/dc/terms/");

---

I try with:

/rdf:RDF/dcat:DataSet/dcat:distribution
//dcat:DataSet/dcat:distribution
//dcat:distribution
/rdf:RDF/dcat:DataSet
//dcat:DataSet

There's a typo. Change DataSet to Dataset.