jena-arq/src/main/java/org/apache/jena/sparql/engine/ResultSetStream.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 org.apache.jena.sparql.engine;

import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.function.Consumer;

import org.apache.jena.atlas.iterator.Iter;
import org.apache.jena.query.QuerySolution;
import org.apache.jena.query.ResultSet;
import org.apache.jena.rdf.model.Model;
import org.apache.jena.sparql.core.ResultBinding;
import org.apache.jena.sparql.core.Var;
import org.apache.jena.sparql.engine.binding.Binding;
import org.apache.jena.sparql.exec.RowSetStream;

/**
 * The main ResultSet implementation for returning results from queries.
 * This version is "use once" - you can not reset the result set because
 * the results of the query are not remembered so as not to consume potentially
 * large amounts of memory.
 */
public class ResultSetStream implements ResultSet
{
    // Could use QueryIteratorWrapper
    private Iterator<Binding> queryExecutionIter;
    private List<String> resultVars;
    private QuerySolution currentQuerySolution;
    private int rowNumber;
    private Model model;

    /** Create a streaming ResultSet, with resources sharing a common Model */
    public static ResultSet create(List<String> resultVars, Model m, Iterator<Binding> iter) {
        return new ResultSetStream(0, resultVars, m, iter);
    }

    /** Create a {@code ResultSet} from a {@literal List<Var>} and an {@literal Iterator<Binding>}. */
    public static ResultSet create(List<Var> resultVars, Iterator<Binding> iter) {
        return ResultSet.adapt(RowSetStream.create(resultVars, iter));
    }

    /** @deprecated Use {@link #create} */
    @Deprecated
    public ResultSetStream(List<String> resultVars, Model m, Iterator<Binding> iter) {
        this(57, resultVars, m, iter);
    }


    protected ResultSetStream(int dummy, List<String> resultVars, Model m, Iterator<Binding> iter) {
        this.queryExecutionIter = iter;
        this.resultVars = resultVars;
        this.currentQuerySolution = null;
        this.rowNumber = 0;
        this.model = m;
    }

    /**
     * Is there another possibility?
     */
    @Override
    public boolean hasNext() {
        if ( queryExecutionIter == null )
            return false;
        boolean r = queryExecutionIter.hasNext();
        if ( !r )
            close();
        return r;
    }

    @Override
    public Binding nextBinding() {
        if ( queryExecutionIter == null )
            throw new NoSuchElementException(this.getClass() + ".next");

        try {
            Binding binding = queryExecutionIter.next();
            if ( binding != null )
                rowNumber++;
            return binding;
        } catch (NoSuchElementException ex) {
            close();
            throw ex;
        }
    }

    @Override
    public void close() {
        // ARQ QueryIterators are org.apache.jena.atlas.lib.Closable.
        Iter.close(queryExecutionIter);
        queryExecutionIter = null;
    }

    /** Moves onto the next result possibility.
     *  The returned object is actual the binding for this
     *  result.
     */
    @Override
    public QuerySolution nextSolution() {
        if ( queryExecutionIter == null )
            throw new NoSuchElementException(this.getClass() + ".next");
        Binding binding = nextBinding();
        currentQuerySolution = new ResultBinding(model, binding);
        return currentQuerySolution;
    }

    /** Moves onto the next result possibility.*/

    @Override
    public QuerySolution next() { return nextSolution(); }

    @Override
    public void forEachRemaining(Consumer<? super QuerySolution> action) {
        if ( queryExecutionIter == null )
            return;
        queryExecutionIter.forEachRemaining(binding -> {
            rowNumber++;
            action.accept(new ResultBinding(model, binding));
        });
        close();
    }

    /** Return the "row number" - a count of the number of possibilities returned so far.
     *  Remains valid (as the total number of possibilities) after the iterator ends.
     */

    @Override
    public int getRowNumber() {
        return rowNumber;
    }

    /** Get the variable names for the projection */
    @Override
    public List<String> getResultVars() { return resultVars; }

    public Model getModel() { return model; }

    @Override
    public Model getResourceModel() { return model; }

}