ChangeSetStore.java

package eu.lod2.rsine.changesetstore;

import org.openrdf.OpenRDFException;
import org.openrdf.model.Graph;
import org.openrdf.model.Statement;
import org.openrdf.query.BindingSet;
import org.openrdf.query.QueryLanguage;
import org.openrdf.query.TupleQueryResult;
import org.openrdf.repository.Repository;
import org.openrdf.repository.RepositoryConnection;
import org.openrdf.repository.RepositoryException;
import org.openrdf.rio.RDFHandlerException;
import org.openrdf.rio.turtle.TurtleWriter;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import java.io.StringWriter;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

@Component
public class ChangeSetStore {

    private final Logger logger = LoggerFactory.getLogger(ChangeSetStore.class);

    @Autowired
    private Repository changeSetRepo;

    public synchronized void persistChangeSet(Graph changeSet) throws RepositoryException {
        RepositoryConnection repCon = changeSetRepo.getConnection();
        repCon.add(changeSet);
        repCon.close();
        logger.debug("created changeset: " +formatChangeSet(changeSet));
    }

    private String formatChangeSet(Graph changeSet) {
        StringWriter sw = new StringWriter();
        TurtleWriter turtleWriter = new TurtleWriter(sw);

        try {
            turtleWriter.startRDF();
            Iterator<Statement> statementIterator = changeSet.iterator();
            while (statementIterator.hasNext()) {
                turtleWriter.handleStatement(statementIterator.next());
            }
            turtleWriter.endRDF();
        }
        catch (RDFHandlerException e) {
            return "Could not format changeset";
        }
        return sw.toString();
    }

    public synchronized Collection<BindingSet> evaluateQuery(String query) throws OpenRDFException {
        Collection<BindingSet> bindingSets = new ArrayList<BindingSet>();

        RepositoryConnection repCon = changeSetRepo.getConnection();
        try {
            TupleQueryResult result = repCon.prepareTupleQuery(QueryLanguage.SPARQL, query).evaluate();

            while (result.hasNext()) {
                bindingSets.add(result.next());
            }

            result.close();
            return bindingSets;
        }
        finally {
            repCon.close();
        }
    }

}