/**
* 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.marmotta.platform.sparql.services.sparqlio.sparqljson;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.nio.charset.Charset;
import java.util.Iterator;
import java.util.List;
import info.aduna.io.IndentingWriter;
import info.aduna.text.StringUtil;
import org.openrdf.model.BNode;
import org.openrdf.model.Literal;
import org.openrdf.model.URI;
import org.openrdf.model.Value;
import org.openrdf.query.Binding;
import org.openrdf.query.BindingSet;
import org.openrdf.query.TupleQueryResultHandlerException;
import org.openrdf.query.resultio.TupleQueryResultFormat;
import org.openrdf.query.resultio.TupleQueryResultWriter;
/**
* A TupleQueryResultWriter that writes query results in the <a
* href="http://www.w3.org/TR/rdf-sparql-json-res/">SPARQL Query Results JSON
* Format</a>.
*/
public class SPARQLResultsJSONWriter implements TupleQueryResultWriter {
/*-----------*
* Variables *
*-----------*/
private IndentingWriter writer;
private boolean firstTupleWritten;
/*--------------*
* Constructors *
*--------------*/
public SPARQLResultsJSONWriter(OutputStream out) {
Writer w = new OutputStreamWriter(out, Charset.forName("UTF-8"));
w = new BufferedWriter(w, 1024);
writer = new IndentingWriter(w);
}
/*---------*
* Methods *
*---------*/
public final TupleQueryResultFormat getTupleQueryResultFormat() {
return TupleQueryResultFormat.JSON;
}
public void startQueryResult(List<String> columnHeaders)
throws TupleQueryResultHandlerException
{
try {
openBraces();
// Write header
writeKey("head");
openBraces();
writeKeyValue("vars", columnHeaders);
closeBraces();
writeComma();
// Write results
writeKey("results");
openBraces();
writeKey("bindings");
openArray();
firstTupleWritten = false;
}
catch (IOException e) {
throw new TupleQueryResultHandlerException(e);
}
}
public void endQueryResult()
throws TupleQueryResultHandlerException
{
try {
closeArray(); // bindings array
closeBraces(); // results braces
closeBraces(); // root braces
writer.flush();
}
catch (IOException e) {
throw new TupleQueryResultHandlerException(e);
}
}
public void handleSolution(BindingSet bindingSet)
throws TupleQueryResultHandlerException
{
try {
if (firstTupleWritten) {
writeComma();
}
else {
firstTupleWritten = true;
}
openBraces(); // start of new solution
Iterator<Binding> bindingIter = bindingSet.iterator();
while (bindingIter.hasNext()) {
Binding binding = bindingIter.next();
writeKeyValue(binding.getName(), binding.getValue());
if (bindingIter.hasNext()) {
writeComma();
}
}
closeBraces(); // end solution
writer.flush();
}
catch (IOException e) {
throw new TupleQueryResultHandlerException(e);
}
}
private void writeKeyValue(String key, String value)
throws IOException
{
writeKey(key);
writeString(value);
}
private void writeKeyValue(String key, Value value)
throws IOException, TupleQueryResultHandlerException
{
writeKey(key);
writeValue(value);
}
private void writeKeyValue(String key, Iterable<String> array)
throws IOException
{
writeKey(key);
writeArray(array);
}
private void writeKey(String key)
throws IOException
{
writeString(key);
writer.write(": ");
}
private void writeValue(Value value)
throws IOException, TupleQueryResultHandlerException
{
writer.write("{ ");
if (value instanceof URI) {
writeKeyValue("type", "uri");
writer.write(", ");
writeKeyValue("value", ((URI)value).toString());
}
else if (value instanceof BNode) {
writeKeyValue("type", "bnode");
writer.write(", ");
writeKeyValue("value", ((BNode)value).getID());
}
else if (value instanceof Literal) {
Literal lit = (Literal)value;
if (lit.getLanguage() != null) {
writeKeyValue("xml:lang", lit.getLanguage());
writer.write(", ");
}
if (lit.getDatatype() != null) {
writeKeyValue("datatype", lit.getDatatype().toString());
writer.write(", ");
}
writeKeyValue("type", "literal");
writer.write(", ");
writeKeyValue("value", lit.getLabel());
}
else {
throw new TupleQueryResultHandlerException("Unknown Value object type: " + value.getClass());
}
writer.write(" }");
}
private void writeString(String value)
throws IOException
{
// Escape special characters
value = StringUtil.gsub("\\", "\\\\", value);
value = StringUtil.gsub("\"", "\\\"", value);
value = StringUtil.gsub("/", "\\/", value);
value = StringUtil.gsub("\b", "\\b", value);
value = StringUtil.gsub("\f", "\\f", value);
value = StringUtil.gsub("\n", "\\n", value);
value = StringUtil.gsub("\r", "\\r", value);
value = StringUtil.gsub("\t", "\\t", value);
writer.write("\"");
writer.write(value);
writer.write("\"");
}
private void writeArray(Iterable<String> array)
throws IOException
{
writer.write("[ ");
Iterator<String> iter = array.iterator();
while (iter.hasNext()) {
String value = iter.next();
writeString(value);
if (iter.hasNext()) {
writer.write(", ");
}
}
writer.write(" ]");
}
private void openArray()
throws IOException
{
writer.write("[");
writer.writeEOL();
writer.increaseIndentation();
}
private void closeArray()
throws IOException
{
writer.writeEOL();
writer.decreaseIndentation();
writer.write("]");
}
private void openBraces()
throws IOException
{
writer.write("{");
writer.writeEOL();
writer.increaseIndentation();
}
private void closeBraces()
throws IOException
{
writer.writeEOL();
writer.decreaseIndentation();
writer.write("}");
}
private void writeComma()
throws IOException
{
writer.write(", ");
writer.writeEOL();
}
}