VIVO-974 Replace streaming variant of sparqlSelectQuery() with serializeGraph() and serializeAll()

webapp/src/edu/cornell/mannlib/vitro/webapp/controller/datatools/dumprestore/DumpModelsAction.java

@@ -16,7 +16,6 @@ import org.apache.commons.logging.LogFactory;
 import edu.cornell.mannlib.vitro.webapp.controller.datatools.dumprestore.DumpRestoreController.BadRequestException;
 import edu.cornell.mannlib.vitro.webapp.modelaccess.ModelAccess.WhichService;
 import edu.cornell.mannlib.vitro.webapp.rdfservice.RDFService;
-import edu.cornell.mannlib.vitro.webapp.rdfservice.RDFService.ResultFormat;
 import edu.cornell.mannlib.vitro.webapp.rdfservice.RDFServiceException;
 
 /**
@@ -70,9 +69,7 @@ class DumpModelsAction extends AbstractDumpRestoreAction {
 	 */
 	private void dumpNQuads(RDFService rdfService, String query)
 			throws RDFServiceException, IOException {
-		JsonToNquads converter = new JsonToNquads(resp.getOutputStream());
+		rdfService.serializeAll(resp.getOutputStream());
-		rdfService.sparqlSelectQuery(query, ResultFormat.JSON, converter);
-		converter.close();
 	}
 
 }

webapp/src/edu/cornell/mannlib/vitro/webapp/controller/datatools/dumprestore/JsonToNquads.java

@@ -1,128 +0,0 @@
-/* $This file is distributed under the terms of the license in /doc/license.txt$ */
-
-package edu.cornell.mannlib.vitro.webapp.controller.datatools.dumprestore;
-
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.OutputStream;
-import java.io.OutputStreamWriter;
-import java.io.StringReader;
-import java.io.Writer;
-
-import javax.json.Json;
-import javax.json.JsonObject;
-import javax.json.JsonReader;
-
-import org.apache.commons.logging.Log;
-import org.apache.commons.logging.LogFactory;
-
-/**
- * An output stream decorator that converts a stream of
- * application/sparql-results+json to a stream of application/n-quads
- * 
- * This could be a lot more efficient.
- */
-public class JsonToNquads extends OutputStream {
-	private static final Log log = LogFactory.getLog(JsonToNquads.class);
-
-	private final Writer writer;
-	private final ByteArrayOutputStream buffer = new ByteArrayOutputStream();
-	private final ByteArrayOutputStream header = new ByteArrayOutputStream();
-
-	private boolean headerIsComplete;
-	private long recordCount;
-
-	public JsonToNquads(OutputStream out) throws IOException {
-		this.writer = new OutputStreamWriter(out, "UTF-8");
-		log.info("Dump beginning.");
-	}
-
-	@Override
-	public void flush() throws IOException {
-		writer.flush();
-	}
-
-	@Override
-	public void close() throws IOException {
-		writer.close();
-		log.info("Dump is complete: " + recordCount + " records.");
-		log.debug("Left over in the buffer: '" + buffer + "'");
-	}
-
-	@Override
-	public void write(int b) throws IOException {
-		if (!headerIsComplete) {
-			writeToHeader(b);
-		} else {
-			buffer.write(b);
-			if (bufferHoldsARecord()) {
-				processRecord();
-				buffer.reset();
-			}
-		}
-	}
-
-	private void writeToHeader(int b) {
-		header.write((byte) b);
-		String text = header.toString();
-		int bindingsHere = text.indexOf("\"bindings\"");
-		int lastColonHere = text.lastIndexOf(":");
-		int lastOpenBracket = text.lastIndexOf("[");
-		headerIsComplete = (bindingsHere >= 0)
-				&& (lastColonHere > bindingsHere)
-				&& (lastOpenBracket > lastColonHere);
-		log.debug("complete=" + headerIsComplete + ", header='" + text + "'");
-	}
-
-	private boolean bufferHoldsARecord() throws IOException {
-		String text = buffer.toString("UTF-8");
-		boolean inQuotes = false;
-		int braceLevel = 0;
-		char previous = 0;
-		for (char c : text.toCharArray()) {
-			if (inQuotes) {
-				if ((c == '"') && (previous != '\\')) {
-					inQuotes = false;
-				}
-			} else {
-				if (c == '"') {
-					inQuotes = true;
-				} else if (c == '{') {
-					braceLevel++;
-				} else if (c == '}') {
-					braceLevel--;
-				}
-			}
-			previous = c;
-		}
-		return (braceLevel == 0) && (text.endsWith(",") || text.endsWith("]"));
-	}
-
-	private void processRecord() throws IOException {
-		String text = buffer.toString("UTF-8");
-		log.debug("Parsing record: '" + text + "'");
-		try (JsonReader jsRead = Json.createReader(new StringReader(text))) {
-			JsonObject jsRecord = jsRead.readObject();
-			DumpNode s = DumpNode.fromJson(jsRecord.getJsonObject("s"));
-			DumpNode p = DumpNode.fromJson(jsRecord.getJsonObject("p"));
-			DumpNode o = DumpNode.fromJson(jsRecord.getJsonObject("o"));
-			DumpNode g = DumpNode.fromJson(jsRecord.getJsonObject("g"));
-
-			if (g == null) {
-				writer.write(String.format("%s %s %s .\n", s.toNquad(),
-						p.toNquad(), o.toNquad()));
-			} else {
-				writer.write(String.format("%s %s %s %s .\n", s.toNquad(),
-						p.toNquad(), o.toNquad(), g.toNquad()));
-			}
-
-			recordCount++;
-			if (recordCount % 10000 == 0) {
-				log.info("dumped " + recordCount + " records.");
-			}
-		} catch (Exception e) {
-			log.error("Failed to parse record: '" + text + "'", e);
-			throw new RuntimeException(e);
-		}
-	}
-}

webapp/src/edu/cornell/mannlib/vitro/webapp/rdfservice/RDFService.java

@@ -87,21 +87,6 @@ public interface RDFService {
 	 */
 	public InputStream sparqlDescribeQuery(String query, RDFService.ModelSerializationFormat resultFormat) throws RDFServiceException;
 	
-	/**
-	 * Performs a SPARQL select query against the knowledge base. The query may have
-	 * an embedded graph identifier. If the query does not contain a graph identifier
-	 * the query is executed against the union of all named and unnamed graphs in the 
-	 * store.
-	 * 
-	 * Preferred for streaming because it avoids in-memory buffering.
-	 * 
-	 * @param query - the SPARQL query to be executed against the RDF store
-	 * @param resultFormat - format for the result of the Select query
-	 * @param outputStream - receives the result of the query 
-	 * 
-	 */
-	public void sparqlSelectQuery(String query, RDFService.ResultFormat resultFormat, OutputStream outputStream) throws RDFServiceException;
-	
 	/**
 	 * Performs a SPARQL select query against the knowledge base. The query may have
 	 * an embedded graph identifier. If the query does not contain a graph identifier
@@ -151,6 +136,29 @@ public interface RDFService {
 	 */
 	public String getDefaultWriteGraphURI() throws RDFServiceException;
 	
+	/**
+	 * Serializes the union of all named and unnamed graphs in the store to the
+	 * supplied OutputStream, in N-Quads format. This method is designed for 
+	 * exporting data from VIVO, so any filters should be bypassed. If possible, 
+	 * this should be done without buffering in memory, so arbitrarily large 
+	 * graphs can be exported.
+	 * 
+	 * @param outputStream - receives the serialized result.
+	 */
+	public void serializeAll(OutputStream outputStream) throws RDFServiceException;
+
+	/**
+	 * Serializes the contents of the named graph to the supplied OutputStream,
+	 * in N-Triples format. This method is designed for exporting data from 
+	 * VIVO, so any filters should be bypassed. If possible, this should be 
+	 * done without buffering in memory, so arbitrarily large graphs can be 
+	 * exported.
+	 * 
+	 * @param graphURI - the URI of the desired graph. May not be null.
+	 * @param outputStream - receives the serialized result.
+	 */
+	public void serializeGraph(String graphURI, OutputStream outputStream) throws RDFServiceException;
+
 	/**
 	 * Registers a listener to listen to changes in any graph in
 	 * the RDF store.

webapp/src/edu/cornell/mannlib/vitro/webapp/rdfservice/filter/LanguageFilteringRDFService.java

@@ -4,7 +4,6 @@ package edu.cornell.mannlib.vitro.webapp.rdfservice.filter;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
-import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.ArrayList;
@@ -13,7 +12,6 @@ import java.util.Comparator;
 import java.util.Iterator;
 import java.util.List;
 
-import org.apache.commons.io.IOUtils;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
@@ -157,20 +155,6 @@ public class LanguageFilteringRDFService implements RDFService {
 		return langStrings.toString();
 	}
 
-	/**
-	 * TODO rewrite the filtering to use this form - avoid one level of
-	 * buffering.
-	 */
-	@Override
-	public void sparqlSelectQuery(String query, ResultFormat resultFormat,
-			OutputStream outputStream) throws RDFServiceException {
-		try (InputStream input = sparqlSelectQuery(query, resultFormat)){
-			IOUtils.copy(input, outputStream);
-		} catch (IOException e) {
-			throw new RDFServiceException(e);
-		}
-	}
-
 	@Override
     public InputStream sparqlSelectQuery(String query,
             ResultFormat resultFormat) throws RDFServiceException {        
@@ -339,6 +323,18 @@ public class LanguageFilteringRDFService implements RDFService {
         return s.getDefaultWriteGraphURI();
     }
 
+    @Override
+	public void serializeAll(OutputStream outputStream)
+			throws RDFServiceException {
+    	s.serializeAll(outputStream);
+	}
+
+	@Override
+	public void serializeGraph(String graphURI, OutputStream outputStream)
+			throws RDFServiceException {
+		s.serializeGraph(graphURI, outputStream);
+	}
+
 	@Override
     public void registerListener(ChangeListener changeListener)
             throws RDFServiceException {

webapp/src/edu/cornell/mannlib/vitro/webapp/rdfservice/filter/SameAsFilteringRDFServiceFactory.java

@@ -4,14 +4,12 @@ package edu.cornell.mannlib.vitro.webapp.rdfservice.filter;
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
-import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.List;
 
-import org.apache.commons.io.IOUtils;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
@@ -107,20 +105,6 @@ public class SameAsFilteringRDFServiceFactory implements RDFServiceFactory {
             return new ByteArrayInputStream(out.toByteArray());
         }
               
-    	/**
-    	 * TODO rewrite the filtering to use this form instead - avoid one level of
-    	 * buffering.
-    	 */
-    	@Override
-    	public void sparqlSelectQuery(String query, ResultFormat resultFormat,
-    			OutputStream outputStream) throws RDFServiceException {
-    		try (InputStream input = sparqlSelectQuery(query, resultFormat)) {
-    			IOUtils.copy(input, outputStream);
-    		} catch (IOException e) {
-    			throw new RDFServiceException(e);
-    		}
-    	}
-    	
         @Override 
         public InputStream sparqlSelectQuery(String query, ResultFormat resultFormat) 
                 throws RDFServiceException {
@@ -256,6 +240,18 @@ public class SameAsFilteringRDFServiceFactory implements RDFServiceFactory {
             s.getGraphMetadata();
         }
 
+        @Override
+    	public void serializeAll(OutputStream outputStream)
+    			throws RDFServiceException {
+        	s.serializeAll(outputStream);
+    	}
+
+    	@Override
+    	public void serializeGraph(String graphURI, OutputStream outputStream)
+    			throws RDFServiceException {
+    		s.serializeGraph(graphURI, outputStream);
+    	}
+
         @Override
         public void close() {
             s.close();

webapp/src/edu/cornell/mannlib/vitro/webapp/rdfservice/impl/RDFServiceFactorySingle.java

@@ -87,12 +87,6 @@ public class RDFServiceFactorySingle implements RDFServiceFactory {
             return s.sparqlDescribeQuery(query, resultFormat);
         }
 
-        @Override
-		public void sparqlSelectQuery(String query, ResultFormat resultFormat,
-				OutputStream outputStream) throws RDFServiceException {
-        	s.sparqlSelectQuery(query, resultFormat, outputStream);
-		}
-
         @Override
         public InputStream sparqlSelectQuery(String query,
                 ResultFormat resultFormat) throws RDFServiceException {
@@ -119,6 +113,18 @@ public class RDFServiceFactorySingle implements RDFServiceFactory {
             return s.getDefaultWriteGraphURI();
         }
 
+        @Override
+    	public void serializeAll(OutputStream outputStream)
+    			throws RDFServiceException {
+        	s.serializeAll(outputStream);
+    	}
+
+    	@Override
+    	public void serializeGraph(String graphURI, OutputStream outputStream)
+    			throws RDFServiceException {
+    		s.serializeGraph(graphURI, outputStream);
+    	}
+
        @Override
         public void registerListener(ChangeListener changeListener)
                 throws RDFServiceException {

webapp/src/edu/cornell/mannlib/vitro/webapp/rdfservice/impl/jena/RDFServiceJena.java

@@ -15,6 +15,7 @@ import java.util.concurrent.ConcurrentLinkedQueue;
 import org.apache.commons.io.IOUtils;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.apache.jena.riot.RDFDataMgr;
 import org.apache.log4j.lf5.util.StreamUtils;
 
 import com.hp.hpl.jena.graph.Triple;
@@ -35,6 +36,7 @@ import com.hp.hpl.jena.rdf.model.Statement;
 import com.hp.hpl.jena.rdf.model.StmtIterator;
 import com.hp.hpl.jena.sdb.SDB;
 import com.hp.hpl.jena.shared.Lock;
+import com.hp.hpl.jena.sparql.core.Quad;
 
 import edu.cornell.mannlib.vitro.webapp.dao.jena.DatasetWrapper;
 import edu.cornell.mannlib.vitro.webapp.dao.jena.SparqlGraph;
@@ -44,6 +46,8 @@ import edu.cornell.mannlib.vitro.webapp.rdfservice.RDFService;
 import edu.cornell.mannlib.vitro.webapp.rdfservice.RDFServiceException;
 import edu.cornell.mannlib.vitro.webapp.rdfservice.impl.RDFServiceImpl;
 import edu.cornell.mannlib.vitro.webapp.utils.logging.ToString;
+import edu.cornell.mannlib.vitro.webapp.utils.sparql.ResultSetIterators.ResultSetQuadsIterator;
+import edu.cornell.mannlib.vitro.webapp.utils.sparql.ResultSetIterators.ResultSetTriplesIterator;
 
 public abstract class RDFServiceJena extends RDFServiceImpl implements RDFService {
 
@@ -430,45 +434,6 @@ public abstract class RDFServiceJena extends RDFServiceImpl implements RDFServic
         return getRDFResultStream(query, DESCRIBE, resultFormat);
     }
 
-	@Override
-	public void sparqlSelectQuery(String query, ResultFormat resultFormat,
-			OutputStream outputStream) throws RDFServiceException {
-		DatasetWrapper dw = getDatasetWrapper();
-		try {
-			Dataset d = dw.getDataset();
-			Query q = createQuery(query);
-			QueryExecution qe = createQueryExecution(query, q, d);
-			// These properties only help for SDB, but shouldn't hurt for TDB.
-			qe.getContext().set(SDB.jdbcFetchSize, Integer.MIN_VALUE);
-			qe.getContext().set(SDB.jdbcStream, true);
-			qe.getContext().set(SDB.streamGraphAPI, true);
-			try {
-				ResultSet resultSet = qe.execSelect();
-				switch (resultFormat) {
-				case CSV:
-					ResultSetFormatter.outputAsCSV(outputStream, resultSet);
-					break;
-				case TEXT:
-					ResultSetFormatter.out(outputStream, resultSet);
-					break;
-				case JSON:
-					ResultSetFormatter.outputAsJSON(outputStream, resultSet);
-					break;
-				case XML:
-					ResultSetFormatter.outputAsXML(outputStream, resultSet);
-					break;
-				default:
-					throw new RDFServiceException("unrecognized result format");
-				}
-			} finally {
-				qe.close();
-			}
-		} finally {
-			dw.close();
-		}
-
-	}
-
 	/**
 	 * TODO Is there a way to accomplish this without buffering the entire result?
 	 */
@@ -547,6 +512,47 @@ public abstract class RDFServiceJena extends RDFServiceImpl implements RDFServic
     	// nothing to do
     }
     
+    @Override
+	public void serializeAll(OutputStream outputStream)
+			throws RDFServiceException {
+    	String query = "SELECT * WHERE { GRAPH ?g {?s ?p ?o}}";
+		serialize(outputStream, query);
+	}
+
+	@Override
+	public void serializeGraph(String graphURI, OutputStream outputStream)
+			throws RDFServiceException {
+		String query = "SELECT * WHERE { GRAPH <" + graphURI + "> {?s ?p ?o}}";
+		serialize(outputStream, query);
+	}
+
+	private void serialize(OutputStream outputStream, String query) {
+		DatasetWrapper dw = getDatasetWrapper();
+		try {
+			Dataset d = dw.getDataset();
+			Query q = createQuery(query);
+			QueryExecution qe = createQueryExecution(query, q, d);
+			// These properties only help for SDB, but shouldn't hurt for TDB.
+			qe.getContext().set(SDB.jdbcFetchSize, Integer.MIN_VALUE);
+			qe.getContext().set(SDB.jdbcStream, true);
+			qe.getContext().set(SDB.streamGraphAPI, true);
+			try {
+				ResultSet resultSet = qe.execSelect();
+				if (resultSet.getResultVars().contains("g")) {
+					Iterator<Quad> quads = new ResultSetQuadsIterator(resultSet);
+					RDFDataMgr.writeQuads(outputStream, quads);
+				} else {
+					Iterator<Triple> triples = new ResultSetTriplesIterator(resultSet);
+					RDFDataMgr.writeTriples(outputStream, triples);
+				}
+			} finally {
+				qe.close();
+			}
+		} finally {
+			dw.close();
+		}
+	}
+
 	@Override
     public void close() {
         // nothing

webapp/src/edu/cornell/mannlib/vitro/webapp/rdfservice/impl/jena/tdb/RDFServiceTDB.java

@@ -124,17 +124,6 @@ public class RDFServiceTDB extends RDFServiceJena {
 		}
 	}
 
-	@Override
-	public void sparqlSelectQuery(String query, ResultFormat resultFormat,
-			OutputStream outputStream) throws RDFServiceException {
-		dataset.getLock().enterCriticalSection(Lock.READ);
-		try {
-			super.sparqlSelectQuery(query, resultFormat, outputStream);
-		} finally {
-			dataset.getLock().leaveCriticalSection();
-		}
-	}
-
 	@Override
 	public InputStream sparqlSelectQuery(String query, ResultFormat resultFormat)
 			throws RDFServiceException {
@@ -166,6 +155,28 @@ public class RDFServiceTDB extends RDFServiceJena {
 		}
 	}
 
+	@Override
+	public void serializeAll(OutputStream outputStream)
+			throws RDFServiceException {
+		dataset.getLock().enterCriticalSection(Lock.READ);
+		try {
+			super.serializeAll(outputStream);
+		} finally {
+			dataset.getLock().leaveCriticalSection();
+		}
+	}
+
+	@Override
+	public void serializeGraph(String graphURI, OutputStream outputStream)
+			throws RDFServiceException {
+		dataset.getLock().enterCriticalSection(Lock.READ);
+		try {
+			super.serializeGraph(graphURI, outputStream);
+		} finally {
+			dataset.getLock().leaveCriticalSection();
+		}
+	}
+
 	@Override
 	public String toString() {
 		return "RDFServiceTDB[" + ToString.hashHex(this) + "]";

webapp/src/edu/cornell/mannlib/vitro/webapp/rdfservice/impl/logging/LoggingRDFService.java

@@ -52,13 +52,6 @@ public class LoggingRDFService implements RDFService {
 		}
 	}
 
-	@Override
-	public void sparqlSelectQuery(String query, ResultFormat resultFormat,
-			OutputStream outputStream) throws RDFServiceException {
-		innerService.sparqlSelectQuery(query, resultFormat,
-				outputStream);
-	}
-	
 	@Override
 	public InputStream sparqlSelectQuery(String query, ResultFormat resultFormat)
 			throws RDFServiceException {
@@ -74,6 +67,22 @@ public class LoggingRDFService implements RDFService {
 		}
 	}
 
+	@Override
+	public void serializeAll(OutputStream outputStream)
+			throws RDFServiceException {
+		try (RDFServiceLogger l = new RDFServiceLogger()) {
+			innerService.serializeAll(outputStream);
+		}
+	}
+
+	@Override
+	public void serializeGraph(String graphURI, OutputStream outputStream)
+			throws RDFServiceException {
+		try (RDFServiceLogger l = new RDFServiceLogger(graphURI)) {
+			innerService.serializeGraph(graphURI, outputStream);
+		}
+	}
+
 	// ----------------------------------------------------------------------
 	// Untimed methods
 	// ----------------------------------------------------------------------

webapp/src/edu/cornell/mannlib/vitro/webapp/rdfservice/impl/sparql/RDFServiceSparql.java

@@ -27,6 +27,7 @@ import org.apache.http.impl.client.CloseableHttpClient;
 import org.apache.http.impl.client.HttpClients;
 import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
 import org.apache.http.message.BasicNameValuePair;
+import org.apache.jena.riot.RDFDataMgr;
 
 import com.hp.hpl.jena.graph.Triple;
 import com.hp.hpl.jena.query.Query;
@@ -43,6 +44,7 @@ import com.hp.hpl.jena.rdf.model.RDFNode;
 import com.hp.hpl.jena.rdf.model.Resource;
 import com.hp.hpl.jena.rdf.model.Statement;
 import com.hp.hpl.jena.rdf.model.StmtIterator;
+import com.hp.hpl.jena.sparql.core.Quad;
 
 import edu.cornell.mannlib.vitro.webapp.dao.jena.SparqlGraph;
 import edu.cornell.mannlib.vitro.webapp.rdfservice.ChangeListener;
@@ -53,6 +55,8 @@ import edu.cornell.mannlib.vitro.webapp.rdfservice.RDFServiceException;
 import edu.cornell.mannlib.vitro.webapp.rdfservice.impl.ChangeSetImpl;
 import edu.cornell.mannlib.vitro.webapp.rdfservice.impl.RDFServiceImpl;
 import edu.cornell.mannlib.vitro.webapp.rdfservice.impl.jena.ListeningGraph;
+import edu.cornell.mannlib.vitro.webapp.utils.sparql.ResultSetIterators.ResultSetQuadsIterator;
+import edu.cornell.mannlib.vitro.webapp.utils.sparql.ResultSetIterators.ResultSetTriplesIterator;
 
 /*
  * API to write, read, and update Vitro's RDF store, with support 
@@ -263,20 +267,6 @@ public class RDFServiceSparql extends RDFServiceImpl implements RDFService {
 		return result;
 	}
 
-	/**
-	 * TODO rewrite the query to use this form instead - avoid one level of
-	 * buffering.
-	 */
-	@Override
-	public void sparqlSelectQuery(String query, ResultFormat resultFormat,
-			OutputStream outputStream) throws RDFServiceException {
-		try (InputStream input = sparqlSelectQuery(query, resultFormat)) {
-			IOUtils.copy(input, outputStream);
-		} catch (IOException e) {
-			throw new RDFServiceException(e);
-		}
-	}
-	
 	/**
 	 * Performs a SPARQL select query against the knowledge base. The query may have
 	 * an embedded graph identifier.
@@ -826,4 +816,31 @@ public class RDFServiceSparql extends RDFServiceImpl implements RDFService {
                 getSerializationFormatString(modelChange.getSerializationFormat()));
         return model;
     }
+
+    @Override
+	public void serializeAll(OutputStream outputStream)
+			throws RDFServiceException {
+    	String query = "SELECT * WHERE { GRAPH ?g {?s ?p ?o}}";
+		serialize(outputStream, query);
+	}
+
+	@Override
+	public void serializeGraph(String graphURI, OutputStream outputStream)
+			throws RDFServiceException {
+		String query = "SELECT * WHERE { GRAPH <" + graphURI + "> {?s ?p ?o}}";
+		serialize(outputStream, query);
+	}
+
+	private void serialize(OutputStream outputStream, String query) throws RDFServiceException {
+        InputStream resultStream = sparqlSelectQuery(query, RDFService.ResultFormat.JSON);
+        ResultSet resultSet = ResultSetFactory.fromJSON(resultStream);
+		if (resultSet.getResultVars().contains("g")) {
+			Iterator<Quad> quads = new ResultSetQuadsIterator(resultSet);
+			RDFDataMgr.writeQuads(outputStream, quads);
+		} else {
+			Iterator<Triple> triples = new ResultSetTriplesIterator(resultSet);
+			RDFDataMgr.writeTriples(outputStream, triples);
+		}
+	}
+
 }

webapp/src/edu/cornell/mannlib/vitro/webapp/utils/sparql/ResultSetIterators.java

@@ -0,0 +1,97 @@
+/* $This file is distributed under the terms of the license in /doc/license.txt$ */
+
+package edu.cornell.mannlib.vitro.webapp.utils.sparql;
+
+import java.util.Iterator;
+
+import com.hp.hpl.jena.graph.Node;
+import com.hp.hpl.jena.graph.NodeFactory;
+import com.hp.hpl.jena.graph.Triple;
+import com.hp.hpl.jena.query.QuerySolution;
+import com.hp.hpl.jena.query.ResultSet;
+import com.hp.hpl.jena.rdf.model.Literal;
+import com.hp.hpl.jena.rdf.model.RDFNode;
+import com.hp.hpl.jena.rdf.model.Resource;
+import com.hp.hpl.jena.sparql.core.Quad;
+
+/**
+ * Helper classes for producing N-Triples or N-Quads from ResultSets
+ */
+public class ResultSetIterators {
+	/**
+	 * If the ResultSet contains appropriate values for g, s, p, and o, return a
+	 * Quad for each row.
+	 */
+	public static class ResultSetQuadsIterator implements Iterator<Quad> {
+		private final ResultSet resultSet;
+
+		public ResultSetQuadsIterator(ResultSet resultSet) {
+			this.resultSet = resultSet;
+		}
+
+		@Override
+		public boolean hasNext() {
+			return resultSet.hasNext();
+		}
+
+		@Override
+		public Quad next() {
+			QuerySolution s = resultSet.next();
+			return new Quad(NodeConverter.toNode(s.get("g")),
+					NodeConverter.toNode(s.get("s")), NodeConverter.toNode(s
+							.get("p")), NodeConverter.toNode(s.get("o")));
+		}
+
+		@Override
+		public void remove() {
+			throw new UnsupportedOperationException();
+		}
+
+	}
+
+	/**
+	 * If the ResultSet contains appropriate values for s, p, and o, return a
+	 * Triple for each row.
+	 */
+	public static class ResultSetTriplesIterator implements Iterator<Triple> {
+		private final ResultSet resultSet;
+
+		public ResultSetTriplesIterator(ResultSet resultSet) {
+			this.resultSet = resultSet;
+		}
+
+		@Override
+		public boolean hasNext() {
+			return resultSet.hasNext();
+		}
+
+		@Override
+		public Triple next() {
+			QuerySolution s = resultSet.next();
+			return new Triple(NodeConverter.toNode(s.get("s")),
+					NodeConverter.toNode(s.get("p")), NodeConverter.toNode(s
+							.get("o")));
+		}
+
+		@Override
+		public void remove() {
+			throw new UnsupportedOperationException();
+		}
+	}
+
+	private static class NodeConverter {
+		public static Node toNode(RDFNode rdfNode) {
+			if (rdfNode.isAnon()) {
+				Resource a = rdfNode.asResource();
+				return NodeFactory.createAnon(a.getId());
+			}
+			if (rdfNode.isLiteral()) {
+				Literal l = rdfNode.asLiteral();
+				return NodeFactory.createLiteral(l.getLexicalForm(),
+						l.getLanguage(), l.getDatatype());
+			}
+			return NodeFactory.createURI(rdfNode.asResource().getURI());
+		}
+	}
+
+}