/**
* Used to write Resources for a Subject. Literals will by-pass this method and use "Literal"
* method.
*
* @param predicate PredicateNode
* @param object ObjectNode
* @param writer PrintWriter
* @throws GraphException
*/
protected void writeStatement(
Graph graph,
SubjectNode subject,
PredicateNode predicate,
ObjectNode object,
PrintWriter writer)
throws GraphException {
// Literals are written differently
if (object instanceof Literal) {
this.writeStatement(graph, subject, predicate, (Literal) object, writer);
} else if (object instanceof BlankNode) {
// write as: <predicateURI> *blank node as subject* </predicateURI>
writer.println(" <" + this.getURI(predicate) + ">");
// write blank node as a "subject"
this.writeSubject(graph, (BlankNode) object, writer);
writer.println(" </" + this.getURI(predicate) + ">");
} else if (subject instanceof BlankNode) {
// predicatNode representing RDF Type
PredicateNode rdfTypeNode = null;
try {
rdfTypeNode = graph.getElementFactory().createResource(RDF.TYPE);
} catch (GraphElementFactoryException factoryException) {
throw new GraphException("Could not create RDF Type node.", factoryException);
}
// do not write the RDF Type element
if (!rdfTypeNode.equals(predicate)) {
// write as: <predicateURI rdf:resource="resourceURI"/>
writer.println(
" <"
+ this.getURI(predicate)
+ " "
+ RDF_PREFIX
+ ":resource=\""
+ this.getNodeString(object)
+ "\"/>");
}
} else {
// write as: <predicateURI rdf:resource="resourceURI"/>
writer.println(
" <"
+ this.getURI(predicate)
+ " "
+ RDF_PREFIX
+ ":resource=\""
+ this.getNodeString(object)
+ "\"/>");
}
}
/**
* Finds the RDF Type for a given subject.
*
* @param graph Graph
* @param subject SubjectNode
* @throws GraphException
* @return ObjectNode
*/
protected ObjectNode getSubjectType(Graph graph, SubjectNode subject) throws GraphException {
// value to be returned
ObjectNode type = null;
// validate graph
if ((graph == null)) {
throw new IllegalArgumentException("Graph argument must not be null.");
}
// predicatNode representing RDF Type
PredicateNode rdfType = null;
try {
rdfType = graph.getElementFactory().createResource(RDF.TYPE);
} catch (GraphElementFactoryException factoryException) {
throw new GraphException("Could not create RDF Type node.", factoryException);
}
// get the Subject's RDF type
ClosableIterator<Triple> typeIter = graph.find(subject, rdfType, null);
if (typeIter != null) {
// validate "first" triple and extract it's object (rdf type)
if (typeIter.hasNext()) {
Triple typeTriple = typeIter.next();
if (typeTriple != null) {
type = ((Triple) typeTriple).getObject();
} else {
throw new GraphException(
"Could not find RDF type for Subject: " + subject + " . Invalid Triple returned.");
}
}
// close the Iterator
typeIter.close();
}
return type;
}
/**
* Populates the namespaces map with default namespaces and namespaces used by the graph.
*
* @param graph Graph
* @throws GraphException
*/
protected void populateNamespaces(Graph graph) throws GraphException {
// default namespaces
namespaces = new HashMap<String, String>();
namespaces.put(RDF_PREFIX, RDF.BASE_URI.toString());
namespaces.put(RDFS_PREFIX, RDFS.BASE_URI.toString());
namespaces.put("owl", "http://www.w3.org/2002/07/owl#");
namespaces.put("dc", "http://purl.org/dc/elements/1.1/");
// validate graph before reading
if (graph == null) {
throw new IllegalArgumentException("Graph argument is null.");
}
// get all statements
ClosableIterator<Triple> tripleIter = graph.find(null, null, null);
if (tripleIter != null) {
while (tripleIter.hasNext()) {
// get the next triple
Triple triple = tripleIter.next();
if (triple != null) {
// evaluate subject
SubjectNode subject = triple.getSubject();
if (subject instanceof URIReference) {
addNamespaceURI(((URIReference) subject).getURI());
}
// evaluate predicate (must be URIReference)
PredicateNode predicate = triple.getPredicate();
addNamespaceURI(((URIReference) predicate).getURI());
// evaluate object
ObjectNode object = triple.getObject();
if (object instanceof URIReference) {
addNamespaceURI(((URIReference) object).getURI());
}
}
}
// close the Iterator
tripleIter.close();
}
}
/**
* Writes the Graph's statements as RDF/XML to the print Writer.
*
* @param out PrintWriter
* @throws IOException
*/
protected void writeBody(Graph graph, PrintWriter out) throws IOException, GraphException {
// validate
if ((out != null) && (graph != null)) {
// iterator used to access subjects
ClosableIterator<Triple> subjectIter = graph.find(null, null, null);
// write every (unique) subject
if (subjectIter != null) {
Set<SubjectNode> writtenSubjectSet = new HashSet<SubjectNode>();
while (subjectIter.hasNext()) {
// get the next triple
Triple triple = subjectIter.next();
if (triple != null) {
SubjectNode subject = ((Triple) triple).getSubject();
if (!writtenSubjectSet.contains(subject)) {
this.writeSubject(graph, subject, out);
writtenSubjectSet.add(subject);
}
}
}
// close the Iterator
subjectIter.close();
}
} else {
// message for exception to be thrown
String message = "Could not write Graph. Invlaid arguments provided. ";
if (out == null) message += "Writer is null. ";
if (graph == null) message += "Graph is null. ";
throw new IllegalArgumentException(message);
}
}
/**
* Writes the Resources for a subject (one per line).
*
* <p>eg. <predicateURI rdf:resource="resourceURI"/> (<predicateURI
* rdf:nodeID="resourceURI"/> for Blank Nodes)
*
* @param graph Graph
* @param subject SubjectNode
* @param writer PrintWriter
* @throws GraphException
*/
protected void writeSubjectBody(Graph graph, SubjectNode subject, PrintWriter writer)
throws GraphException {
// validate graph
/*
if (! (graph instanceof JRDFGraph)) {
throw new IllegalArgumentException("Graph must be of type JRDFGraph");
}
*/
// get all statements for the Subject
ClosableIterator<Triple> tripleIter = graph.find(subject, null, null);
if (tripleIter != null) {
// current Triple
Object triple = null;
// evaluate all triples
while (tripleIter.hasNext()) {
triple = tripleIter.next();
// validate triple
if (triple != null) {
// retrieve Predicate and Object
PredicateNode predicate = ((Triple) triple).getPredicate();
ObjectNode object = ((Triple) triple).getObject();
// Literals and Resources are written differently
if (object != null) {
writeStatement(graph, subject, predicate, object, writer);
}
}
}
// close the Iterator
tripleIter.close();
}
}