RemoteSPARQLEndpoint.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.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLEncoder;
import java.util.Collection;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.openrdf.model.URI;
import org.openrdf.rio.rdfxml.RDFXMLParser;

import com.ontotext.ordi.tripleset.ORDIConst;

import eu.larkc.core.data.DataSet;
import eu.larkc.core.data.DataSetImpl;
import eu.larkc.core.data.RdfGraph;
import eu.larkc.core.data.RdfGraphDataSet;
import eu.larkc.core.data.SPARQLEndpoint;
import eu.larkc.core.data.SetOfStatements;
import eu.larkc.core.data.VariableBinding;

/**
 * RemoteSPARQLEndpoint class automates the result reading from a specific
 * SPARQL endpoint available on the web.
 * 
 * @author vassil
 * 
 */
public class RemoteSPARQLEndpoint implements SPARQLEndpoint {

	private URI uri;

	public RemoteSPARQLEndpoint(URI uri) {
		if (uri == null) {
			throw new IllegalArgumentException();
		}
		this.uri = uri;
	}

	@Override
	public DataSet createDataSet(Collection<URI> defaultGraphs,
			Collection<URI> namedGraphs) {
		return new DataSetImpl(this, defaultGraphs, namedGraphs);
	}

	@Override
	public RdfGraph createRdfGraph(URI graph) {
		return new RdfGraphDataSet(graph, this);
	}

	@Override
	public boolean executeAsk(SPARQLQuery query) {
		if (query == null) {
			throw new IllegalArgumentException("Null value is not supported!");
		}
		if (query.isAsk() == false) {
			throw new IllegalArgumentException("Only ask queries are supported!");
		}
		try {
			final InputStream rstr = sendHTTPGet(query);
			final SAXParserFactory factory = SAXParserFactory.newInstance();
			final SAXParser saxParser = factory.newSAXParser();
			final BooleanXmlVariableBinding result = new BooleanXmlVariableBinding();
			saxParser.parse(rstr, result.getDefaultHandler());
			return result.getResult();
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	@Override
	public SetOfStatements executeConstruct(SPARQLQuery query) {
		if (query == null) {
			throw new IllegalArgumentException("Null value is not supported!");
		}
		if (query.isSelect() == true || query.isAsk() == true ) {
			throw new IllegalArgumentException("Only construct queries are supported!");
		}
		final InputStream rstr = sendHTTPGet(query);
		final RDFXMLParser parser = new RDFXMLParser();
		final RDFXMLGraphResult result = new RDFXMLGraphResult();
		parser.setRDFHandler(result.getRDFHandler());
		Runnable task = new Runnable() {
			public void run() {
				try {
					parser.parse(rstr, ORDIConst.DEFAULT_GRAPH);
				} catch (Exception e) {
					throw new RuntimeException(e);
				}
			}
		};
		Thread t = new Thread(task);
		t.start();
		return result;

	}

	@Override
	public VariableBinding executeSelect(SPARQLQuery query) {
		if (query == null) {
			throw new IllegalArgumentException("Null value is not supported!");
		}
		if (query.isSelect() == false) {
			throw new IllegalArgumentException("Only selecte queries are supported!");
		}
		try {
			final InputStream rstr = sendHTTPGet(query);
			final SAXParserFactory factory = SAXParserFactory.newInstance();
			final SAXParser saxParser = factory.newSAXParser();
			final SelectXMLVariableBinding result = new SelectXMLVariableBinding();
			Runnable task = new Runnable() {
				public void run() {
					try {
						saxParser.parse(rstr, result.getDefaultHandler());
					} catch (Exception e) {
						throw new RuntimeException(e);
					}
				}
			};
			Thread t = new Thread(task);
			t.start();
			return result;
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	public InputStream sendHTTPGet(SPARQLQuery query) {
		URL queryURL = null;

		try {
			String qs = URLEncoder.encode(query.toString(), "UTF-8");
			queryURL = new URL(uri.stringValue()
					+ (uri.stringValue().endsWith("?query=") ? "" : "?query=")
					+ qs);
			URLConnection con = queryURL.openConnection();
			con.setRequestProperty("User-agent", "larkc-datalayer");
			if (query.isConstruct() || query.isDescribe()) {
				con.setRequestProperty("Accept", "application/rdf+xml");
			} else {
				con.setRequestProperty("Accept",
						"application/sparql-results+xml");
			}
			return con.getInputStream();
		} catch (IOException ioe) {
			throw new RuntimeException("Could not load the remote URL file:"
					+ queryURL);
		}
	}
}