jena-arq/src-examples/arq/examples/riot/ExRIOT4_StreamRDF_Filter.java

/*
 * 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 arq.examples.riot;

import org.apache.jena.graph.Node;
import org.apache.jena.graph.Triple;
import org.apache.jena.rdf.model.Property;
import org.apache.jena.riot.RDFParser;
import org.apache.jena.riot.system.StreamRDF;
import org.apache.jena.riot.system.StreamRDFLib;
import org.apache.jena.riot.system.StreamRDFWrapper;
import org.apache.jena.sparql.vocabulary.FOAF;

/** Example of using RIOT : extract only certain properties from a parser run */
public class ExRIOT4_StreamRDF_Filter {
    public static void main(String...argv) {
        String filename = "data.ttl";

        // Write a stream out. 
        StreamRDF output = StreamRDFLib.writer(System.out);
        
        // Wrap in a filter.
        StreamRDF filtered = new FilterSinkRDF(output, FOAF.name, FOAF.knows);

        // Call the parsing process.
        RDFParser.source(filename).parse(filtered);
    }

    // The filtering StreamRDF
    static class FilterSinkRDF extends StreamRDFWrapper {
        private final Node[] properties;

        FilterSinkRDF(StreamRDF dest, Property...properties) {
            super(dest);
            this.properties = new Node[properties.length];
            for ( int i = 0 ; i < properties.length ; i++ )
                this.properties[i] = properties[i].asNode();
        }

        @Override
        public void triple(Triple triple) {
            for ( Node p : properties ) {
                if ( triple.getPredicate().equals(p) )
                    super.triple(triple);
            }
        }
    }
}