ORDIGraphResult.java

/*
   This file is part of the LarKC platform 
   http://www.larkc.eu/

   Copyright 2010 LarKC project consortium

   Licensed 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 eu.larkc.core.query;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.List;
import java.util.concurrent.ArrayBlockingQueue;

import org.openrdf.model.Resource;
import org.openrdf.model.Statement;
import org.openrdf.model.URI;
import org.openrdf.model.impl.StatementImpl;
import org.openrdf.query.BindingSet;
import org.openrdf.query.TupleQueryResultHandler;
import org.openrdf.query.TupleQueryResultHandlerException;

import eu.larkc.core.data.CloseableIterator;
import eu.larkc.core.data.SetOfStatements;

/**
 * ORDIGraphResult implements asynchronous RDF statement result reading from
 * in-memory Sesame-compatible SPARQL endpoint.
 * 
 * @author vassil
 * 
 */
public class ORDIGraphResult extends GraphResultBase implements TupleQueryResultHandler {

	private String[] bindNames;
	private final static long serialVersionUID = 1L;

	public synchronized void startQueryResult(List<String> list) {
		bindNames = list.toArray(new String[list.size()]);
		if (bindNames.length < 3) {
			throw new RuntimeException("Incorrect query projection!");
		}
	}

	public synchronized void endQueryResult() {
		while (true) {
			try {
				results.put(new FinalStatement());
				return;
			} catch (InterruptedException ie) {
			}
		}
	}

	public synchronized void handleSolution(BindingSet bindingset)
			throws TupleQueryResultHandlerException {
		if (isClosed) {
			throw new TupleQueryResultHandlerException("Closed!");
		}
		Statement s = new StatementImpl((Resource) bindingset
				.getValue(bindNames[0]), (URI) bindingset
				.getValue(bindNames[1]), bindingset.getValue(bindNames[2]));

		while (true) {
			try {
				results.put(s);
				return;
			} catch (InterruptedException ie) {
			}
		}
	}

	public synchronized void close() {
		isClosed = true;
	}
	
	// Custom serialization methods
	private void writeObject(ObjectOutputStream out) throws IOException {
		CloseableIterator<Statement> i = getStatements();
		// used to wait until the bindNames field is init
		out.writeObject(bindNames);
		out.writeBoolean(i.hasNext());
		while (i.hasNext()) {
			out.writeObject(i.next());
			out.writeBoolean(i.hasNext());
		}
		out.flush();
		isClosed = true;
	}

	@SuppressWarnings("unchecked")
	private void readObject(ObjectInputStream in) throws IOException,
			ClassNotFoundException {
		this.results = new ArrayBlockingQueue<Statement>(1024);
		bindNames = (String[]) in.readObject();
		while (in.readBoolean()) {
			Statement s = (Statement) in.readObject();
			results.add(s);
		}
		results.add(new FinalStatement());
	}

	/* (non-Javadoc)
	 * @see eu.larkc.core.data.InformationSet#toRDF(eu.larkc.core.data.SetOfStatements)
	 */
	@Override
	public SetOfStatements toRDF(SetOfStatements data) {
		throw new RuntimeException("Not implemented!");
	}
}