/**
* Query SPARQL endpoint with a SELECT query
*
* @param qExec QueryExecution encapsulating the query
* @return model retrieved by querying the endpoint
*/
private Model getSelectModel(QueryExecution qExec) {
Model model = ModelFactory.createDefaultModel();
Graph graph = model.getGraph();
ResultSet results = qExec.execSelect();
while (results.hasNext()) {
QuerySolution sol = results.next();
String subject;
String predicate;
RDFNode object;
try {
subject = sol.getResource("s").toString();
predicate = sol.getResource("p").toString();
object = sol.get("o");
} catch (NoSuchElementException e) {
logger.error("SELECT query does not return a (?s ?p ?o) Triple");
continue;
}
Node objNode;
if (object.isLiteral()) {
Literal obj = object.asLiteral();
objNode = NodeFactory.createLiteral(obj.getString(), obj.getDatatype());
} else {
objNode = NodeFactory.createLiteral(object.toString());
}
graph.add(
new Triple(NodeFactory.createURI(subject), NodeFactory.createURI(predicate), objNode));
}
return model;
}
/**
* Get a set of unique queryObjName returned from a select query
*
* <p>Used to retrieve sets of modified objects used in sync
*
* @param rdfQuery query to execute
* @param queryObjName name of the object returned
* @return set of values for queryObjectName in the rdfQuery result
*/
HashSet<String> executeSyncQuery(String rdfQuery, String queryObjName) {
HashSet<String> rdfUrls = new HashSet<String>();
Query query;
try {
query = QueryFactory.create(rdfQuery);
} catch (QueryParseException qpe) {
logger.warn(
"Could not parse [{}]. Please provide a relevant query. {}",
rdfQuery,
qpe.getLocalizedMessage());
return null;
}
QueryExecution qExec = QueryExecutionFactory.sparqlService(rdfEndpoint, query);
try {
ResultSet results = qExec.execSelect();
while (results.hasNext()) {
QuerySolution sol = results.nextSolution();
try {
String value = sol.getResource(queryObjName).toString();
rdfUrls.add(value);
} catch (NoSuchElementException e) {
logger.error("Encountered a NoSuchElementException: " + e.getLocalizedMessage());
return null;
}
}
} catch (Exception e) {
logger.error(
"Encountered a [{}] while querying the endpoint for sync", e.getLocalizedMessage());
return null;
} finally {
qExec.close();
}
return rdfUrls;
}
