org.apache.marmotta.ldcache.sail.GenericLinkedDataSailConnection Maven / Gradle / Ivy

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Stacked Sail that allows transparent access to resources through the Linked Data Cache, retrieving them on demand when needed. Can be wrapped around other Sesame SAILs.

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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.marmotta.ldcache.sail;

import info.aduna.iteration.CloseableIteration;
import info.aduna.iteration.CloseableIteratorIteration;
import info.aduna.iteration.UnionIteration;
import org.apache.marmotta.commons.sesame.filter.AlwaysTrueFilter;
import org.apache.marmotta.commons.sesame.filter.SesameFilter;
import org.apache.marmotta.commons.sesame.repository.ResourceUtils;
import org.apache.marmotta.ldcache.services.LDCache;
import org.openrdf.model.*;
import org.openrdf.sail.NotifyingSailConnection;
import org.openrdf.sail.SailException;
import org.openrdf.sail.helpers.NotifyingSailConnectionWrapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * A sail connection wrapper that queries both the wrapped connection and the cached triples provided by an
 * LDCache instance.
 *
 * @author Sebastian Schaffert ([email protected])
 * @author Jakob Frank ([email protected])
 */
public class GenericLinkedDataSailConnection extends NotifyingSailConnectionWrapper {

    private static Logger log = LoggerFactory.getLogger(GenericLinkedDataSailConnection.class);

    private final LDCache ldcache;
    private final SesameFilter acceptForCaching;

    public GenericLinkedDataSailConnection(NotifyingSailConnection connection, LDCache ldcache) {
        this(connection, ldcache, new AlwaysTrueFilter());
    }


    public GenericLinkedDataSailConnection(NotifyingSailConnection connection, LDCache ldcache, SesameFilter acceptForCaching) {
        super(connection);
        this.ldcache = ldcache;
        this.acceptForCaching = acceptForCaching;
    }

    /**
     * Get the statements for the query pattern passed as arguments. In case the subject resource is acceptable for caching,
     * refreshes the cache for this resource and returns a merged query result together with the wrapped connection.
     * Otherwise, simply delegates to the wrapped connection.
     *
     * @param subj
     * @param pred
     * @param obj
     * @param includeInferred
     * @param contexts
     * @return
     * @throws SailException
     */
    @Override
    public CloseableIteration getStatements(Resource subj, URI pred, Value obj, boolean includeInferred, Resource... contexts) throws SailException {

        if (accept(subj)) {
            log.debug("Refreshing resource: {}", subj.stringValue());
            final Model cached = ldcache.get((URI)subj);

            // join the results of the cache connection and the wrapped connection in a single result
            return new UnionIteration(
                    new CloseableIteratorIteration(cached.iterator()),
                    super.getStatements(subj, pred, obj, includeInferred, contexts)
            );
        } else {
            return super.getStatements(subj, pred, obj, includeInferred, contexts);
        }
    }


    private boolean accept(Resource subj) {
        return subj != null && ResourceUtils.isURI(subj) && acceptForCaching.accept(subj);
    }

}