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Andrew Woods
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Create SPARQL datasource
- Starting from 'tdb' example Resolves: LinkedDataFragments#57
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‎src/main/java/org/linkeddatafragments/datasource/sparql/SparqlBasedRequestProcessorForTPFs.java

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package org.linkeddatafragments.datasource.sparql;
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import java.io.File;
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import org.apache.jena.query.Dataset;
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import org.apache.jena.query.Query;
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import org.apache.jena.query.QueryExecution;
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import org.apache.jena.query.QueryExecutionFactory;
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import org.apache.jena.query.QueryFactory;
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import org.apache.jena.query.QuerySolution;
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import org.apache.jena.query.QuerySolutionMap;
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import org.apache.jena.query.ResultSet;
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import org.apache.jena.query.Syntax;
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import org.apache.jena.rdf.model.Literal;
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import org.apache.jena.rdf.model.Model;
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import org.apache.jena.rdf.model.ModelFactory;
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import org.apache.jena.rdf.model.RDFNode;
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import org.apache.jena.tdb.TDBFactory;
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import org.linkeddatafragments.datasource.AbstractRequestProcessorForTriplePatterns;
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import org.linkeddatafragments.datasource.IFragmentRequestProcessor;
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import org.linkeddatafragments.fragments.ILinkedDataFragment;
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import org.linkeddatafragments.fragments.tpf.ITriplePatternElement;
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import org.linkeddatafragments.fragments.tpf.ITriplePatternFragmentRequest;
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/**
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* Implementation of {@link IFragmentRequestProcessor} that processes
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* {@link ITriplePatternFragmentRequest}s over data stored in Jena TDB.
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*
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* @author <a href="mailto:[email protected]">Bart Hanssens</a>
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* @author <a href="http://olafhartig.de">Olaf Hartig</a>
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*/
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public class SparqlBasedRequestProcessorForTPFs
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extends AbstractRequestProcessorForTriplePatterns<RDFNode,String,String>
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{
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private final Dataset tdb;
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private final String defaultGraph;
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private final String sparql = "CONSTRUCT WHERE { ?s ?p ?o } " +
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"ORDER BY ?s ?p ?o";
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private final String count = "SELECT (COUNT(?s) AS ?count) WHERE { ?s ?p ?o }";
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private final Query query = QueryFactory.create(sparql, Syntax.syntaxSPARQL_11);
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private final Query countQuery = QueryFactory.create(count, Syntax.syntaxSPARQL_11);
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/**
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*
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* @param request
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* @return
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* @throws IllegalArgumentException
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*/
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@Override
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protected Worker getTPFSpecificWorker(
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final ITriplePatternFragmentRequest<RDFNode,String,String> request )
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throws IllegalArgumentException
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{
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return new Worker( request );
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}
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/**
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*
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*/
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protected class Worker
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extends AbstractRequestProcessorForTriplePatterns.Worker<RDFNode,String,String>
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{
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/**
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*
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* @param req
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*/
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public Worker(
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final ITriplePatternFragmentRequest<RDFNode,String,String> req )
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{
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super( req );
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}
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/**
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*
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* @param subject
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* @param predicate
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* @param object
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* @param offset
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* @param limit
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* @return
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*/
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@Override
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protected ILinkedDataFragment createFragment(
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final ITriplePatternElement<RDFNode,String,String> subject,
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final ITriplePatternElement<RDFNode,String,String> predicate,
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final ITriplePatternElement<RDFNode,String,String> object,
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final long offset,
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final long limit )
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{
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// FIXME: The following algorithm is incorrect for cases in which
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// the requested triple pattern contains a specific variable
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// multiple times;
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// e.g., (?x foaf:knows ?x ) or (_:bn foaf:knows _:bn)
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// see https://github.com/LinkedDataFragments/Server.Java/issues/24
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Model model;
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if (defaultGraph == null) {
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model = tdb.getDefaultModel();
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} else {
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model = tdb.getNamedModel(defaultGraph);
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}
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QuerySolutionMap map = new QuerySolutionMap();
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if ( ! subject.isVariable() ) {
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map.add("s", subject.asConstantTerm());
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}
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if ( ! predicate.isVariable() ) {
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map.add("p", predicate.asConstantTerm());
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}
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if ( ! object.isVariable() ) {
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map.add("o", object.asConstantTerm());
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}
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query.setOffset(offset);
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query.setLimit(limit);
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Model triples = ModelFactory.createDefaultModel();
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try (QueryExecution qexec = QueryExecutionFactory.create(query, model, map)) {
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qexec.execConstruct(triples);
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}
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if (triples.isEmpty()) {
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return createEmptyTriplePatternFragment();
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}
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// Try to get an estimate
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long size = triples.size();
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long estimate = -1;
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try (QueryExecution qexec = QueryExecutionFactory.create(countQuery, model, map)) {
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ResultSet results = qexec.execSelect();
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if (results.hasNext()) {
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QuerySolution soln = results.nextSolution() ;
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Literal literal = soln.getLiteral("count");
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estimate = literal.getLong();
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}
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}
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/*GraphStatisticsHandler stats = model.getGraph().getStatisticsHandler();
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if (stats != null) {
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Node s = (subject != null) ? subject.asNode() : null;
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Node p = (predicate != null) ? predicate.asNode() : null;
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Node o = (object != null) ? object.asNode() : null;
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estimate = stats.getStatistic(s, p, o);
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}*/
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// No estimate or incorrect
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if (estimate < offset + size) {
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estimate = (size == limit) ? offset + size + 1 : offset + size;
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}
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// create the fragment
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final boolean isLastPage = ( estimate < offset + limit );
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return createTriplePatternFragment( triples, estimate, isLastPage );
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}
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} // end of class Worker
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/**
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* Constructor
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*
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* @param tdbdir directory used for TDB backing
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*/
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public SparqlBasedRequestProcessorForTPFs(File tdbdir) {
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this(tdbdir, null);
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}
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public SparqlBasedRequestProcessorForTPFs(File tdbdir, String defaultGraph) {
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this.defaultGraph = defaultGraph;
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this.tdb = TDBFactory.createDataset(tdbdir.getAbsolutePath());
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}
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}

‎src/main/java/org/linkeddatafragments/datasource/sparql/SparqlDataSource.java

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package org.linkeddatafragments.datasource.sparql;
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import java.io.File;
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import org.linkeddatafragments.datasource.DataSourceBase;
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import org.linkeddatafragments.datasource.IFragmentRequestProcessor;
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import org.linkeddatafragments.fragments.IFragmentRequestParser;
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import org.linkeddatafragments.fragments.tpf.TPFRequestParserForJenaBackends;
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/**
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* Experimental Jena TDB-backed data source of Basic Linked Data Fragments.
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*
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* @author <a href="mailto:[email protected]">Bart Hanssens</a>
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* @author <a href="http://olafhartig.de">Olaf Hartig</a>
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*/
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public class SparqlDataSource extends DataSourceBase {
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/**
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* The request processor
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*
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*/
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protected final SparqlBasedRequestProcessorForTPFs requestProcessor;
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@Override
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public IFragmentRequestParser getRequestParser()
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{
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return TPFRequestParserForJenaBackends.getInstance();
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}
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@Override
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public IFragmentRequestProcessor getRequestProcessor()
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{
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return requestProcessor;
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}
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/**
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* Constructor
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*
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* @param title
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* @param description
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* @param tdbdir directory used for TDB backing
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*/
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public SparqlDataSource(String title, String description, File tdbdir, String graph) {
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super(title, description);
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requestProcessor = new SparqlBasedRequestProcessorForTPFs( tdbdir , graph);
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}
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}

‎src/main/java/org/linkeddatafragments/datasource/sparql/SparqlDataSourceType.java

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package org.linkeddatafragments.datasource.sparql;
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import java.io.File;
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import org.linkeddatafragments.datasource.IDataSource;
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import org.linkeddatafragments.datasource.IDataSourceType;
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import org.linkeddatafragments.exceptions.DataSourceCreationException;
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import com.google.gson.JsonObject;
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/**
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* The type of Triple Pattern Fragment data sources that are backed by
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* a Jena TDB instance.
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*
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* @author <a href="http://olafhartig.de">Olaf Hartig</a>
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*/
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public class SparqlDataSourceType implements IDataSourceType
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{
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@Override
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public IDataSource createDataSource( final String title,
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final String description,
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final JsonObject settings )
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throws DataSourceCreationException
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{
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final String dname = settings.getAsJsonPrimitive("directory").getAsString();
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final File dir = new File( dname );
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// Set the defaultGraph, if provided
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String graph = null;
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if (settings.has("graph")) {
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graph = settings.getAsJsonPrimitive("graph").getAsString();
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}
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try {
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return new SparqlDataSource(title, description, dir, graph);
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} catch (Exception ex) {
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throw new DataSourceCreationException(ex);
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}
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}
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}

‎src/test/java/org/linkeddatafragments/test/datasource/SparqlDataSourceTest.java

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package org.linkeddatafragments.test.datasource;
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import com.google.gson.JsonObject;
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import org.apache.jena.query.Dataset;
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import org.apache.jena.rdf.model.Model;
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import org.apache.jena.tdb.TDBFactory;
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import java.io.File;
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import java.io.InputStream;
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import org.apache.jena.rdf.model.RDFNode;
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import org.apache.jena.riot.Lang;
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import org.apache.jena.riot.RDFDataMgr;
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import org.junit.After;
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import org.junit.AfterClass;
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import org.junit.Before;
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import org.junit.BeforeClass;
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import org.linkeddatafragments.datasource.DataSourceFactory;
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import org.linkeddatafragments.datasource.DataSourceTypesRegistry;
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import org.linkeddatafragments.datasource.sparql.SparqlDataSourceType;
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import org.linkeddatafragments.datasource.tdb.JenaTDBDataSourceType;
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import org.linkeddatafragments.util.TriplePatternElementParser;
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import org.linkeddatafragments.util.TriplePatternElementParserForJena;
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/**
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*
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* @author <a href="mailto:[email protected]">Bart Hanssens</a>
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*/
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public class SparqlDataSourceTest extends DataSourceTest<RDFNode,String,String>
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{
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private static File jena;
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private static Dataset dataset;
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/**
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*
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* @return
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*/
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@Override
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protected TriplePatternElementParser<RDFNode,String,String>
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getTriplePatternElementParser()
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{
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return TriplePatternElementParserForJena.getInstance();
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}
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/**
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*
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* @throws Exception
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*/
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@BeforeClass
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public static void setUpClass() throws Exception {
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final String typeName = "SparqlSourceType";
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if ( ! DataSourceTypesRegistry.isRegistered(typeName) ) {
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DataSourceTypesRegistry.register( typeName,
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new SparqlDataSourceType() );
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}
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String tmpdir = System.getProperty("java.io.tmpdir");
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jena = new File(tmpdir, "ldf-jena-test");
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jena.mkdir();
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dataset = TDBFactory.createDataset(jena.getAbsolutePath());
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Model model = dataset.getDefaultModel();
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InputStream in = ClassLoader.getSystemResourceAsStream("demo.nt");
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RDFDataMgr.read(model, in, Lang.NTRIPLES);
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// Everything is in place, now create the LDF datasource
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JsonObject config = createConfig("jena tdb test", "jena tdb test",
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typeName);
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JsonObject settings = new JsonObject();
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settings.addProperty("directory", jena.getAbsolutePath());
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config.add("settings", settings);
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setDatasource(DataSourceFactory.create(config));
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}
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/**
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*
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* @throws Exception
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*/
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@AfterClass
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public static void tearDownClass() throws Exception {
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TDBFactory.release(dataset);
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File[] files = jena.listFiles();
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for (File f : files) {
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f.delete();
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}
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jena.delete();
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}
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/**
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*
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* @throws Exception
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*/
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@Before
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public void setUp() throws Exception {
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}
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/**
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*
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* @throws Exception
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*/
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@After
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public void tearDown() throws Exception {
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}
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}

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