/**
* Copyright 2005-2014 Restlet
*
* The contents of this file are subject to the terms of one of the following
* open source licenses: Apache 2.0 or or EPL 1.0 (the "Licenses"). You can
* select the license that you prefer but you may not use this file except in
* compliance with one of these Licenses.
*
* You can obtain a copy of the Apache 2.0 license at
* http://www.opensource.org/licenses/apache-2.0
*
* You can obtain a copy of the EPL 1.0 license at
* http://www.opensource.org/licenses/eclipse-1.0
*
* See the Licenses for the specific language governing permissions and
* limitations under the Licenses.
*
* Alternatively, you can obtain a royalty free commercial license with less
* limitations, transferable or non-transferable, directly at
* http://restlet.com/products/restlet-framework
*
* Restlet is a registered trademark of Restlet S.A.S.
*/
package org.restlet.ext.rdf.internal.xml;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import org.restlet.Context;
import org.restlet.data.Reference;
import org.restlet.ext.rdf.Graph;
import org.restlet.ext.rdf.GraphHandler;
import org.restlet.ext.rdf.Link;
import org.restlet.ext.rdf.Literal;
import org.restlet.ext.rdf.internal.RdfConstants;
import org.restlet.ext.xml.XmlWriter;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.AttributesImpl;
/**
* Handler of RDF content according to the RDF XML syntax.
*
* @author Thierry Boileau
*/
public class RdfXmlWriter extends GraphHandler {
/** The last source reference written, to try to factor statements. */
private Reference lastSource;
/** URI of the RDF SYNTAX namespace. */
private final String RDF_SYNTAX = RdfConstants.RDF_SYNTAX.toString(true,
true);
/** XML writer. */
private XmlWriter writer;
/**
* Constructor.
*
* @param writer
* The character writer.
* @throws UnsupportedEncodingException
*/
public RdfXmlWriter(Writer writer) throws UnsupportedEncodingException {
super();
this.writer = new XmlWriter(writer);
this.lastSource = null;
}
@Override
public void endGraph() throws IOException {
try {
if (this.lastSource != null) {
// We need to end the previous source
this.writer.endElement(RDF_SYNTAX, "Description");
}
this.writer.endElement(RDF_SYNTAX, "RDF");
this.writer.endDocument();
} catch (SAXException e) {
Context.getCurrentLogger().warning(
"Cannot write the end of the graph: " + e.getMessage());
}
this.writer.flush();
}
/**
* Returns the namespace of the given reference.
*
* @param reference
* the given reference.
* @return The namespace of the given reference.
*/
private String getNamespace(Reference reference) {
String prefix = getPrefix(reference);
String ref = reference.toString(true, true);
if (prefix != null) {
return ref.substring(0, ref.length() - prefix.length());
}
return ref;
}
/**
* Returns the prefix of the qualified name representing the given
* reference.
*
* @param ref
* the given reference.
* @return The prefix of the qualified name representing the given
* reference. Context .getCurrentLogger() .warning(
* "Cannot write the end of the graph" + e.getMessage());
*/
private String getPrefix(Reference ref) {
String result = null;
if (ref.hasFragment()) {
result = ref.getFragment();
} else {
result = ref.getLastSegment();
}
return result;
}
@Override
public void link(Graph source, Reference typeRef, Literal target) {
Context.getCurrentLogger()
.warning(
"Cannot write the representation of a statement due to the fact that the subject is not a Reference.");
}
@Override
public void link(Graph source, Reference typeRef, Reference target) {
Context.getCurrentLogger()
.warning(
"Cannot write the representation of a statement due to the fact that the subject is not a Reference.");
}
@Override
public void link(Reference source, Reference typeRef, Literal target) {
try {
if (this.lastSource == null) {
writeNode(source, true);
} else if (!source.equals(this.lastSource)) {
// We need to first end the previous source
this.writer.endElement(RDF_SYNTAX, "Description");
writeNode(source, true);
}
this.lastSource = source;
String typeRefNs = getNamespace(typeRef.getTargetRef());
String typeRefPrefix = getPrefix(typeRef.getTargetRef());
if (target.getLanguage() != null || target.getDatatypeRef() != null) {
AttributesImpl attr = new AttributesImpl();
if (target.getLanguage() != null) {
attr.addAttribute(null, "lang", "xml:lang", "text", target
.getLanguage().getName());
}
if (target.getDatatypeRef() != null) {
attr.addAttribute(RDF_SYNTAX, "datatype", "rdf:datatype",
"text", target.getDatatypeRef()
.toString(true, true));
}
this.writer.startElement(typeRefNs, typeRefPrefix, null, attr);
} else {
this.writer.startElement(typeRefNs, typeRefPrefix);
}
this.writer.characters(target.getValue());
this.writer.endElement(typeRefNs, typeRefPrefix);
} catch (SAXException e) {
org.restlet.Context.getCurrentLogger().warning(
"Cannot write the representation of a statement due to: "
+ e.getMessage());
}
}
@Override
public void link(Reference source, Reference typeRef, Reference target) {
try {
if (this.lastSource == null) {
writeNode(source, true);
} else if (!source.equals(this.lastSource)) {
// We need to first end the previous source
this.writer.endElement(RDF_SYNTAX, "Description");
writeNode(source, true);
}
this.lastSource = source;
String typeRefNs = getNamespace(typeRef.getTargetRef());
String typeRefPrefix = getPrefix(typeRef.getTargetRef());
this.writer.startElement(typeRefNs, typeRefPrefix);
writeNode(target, false);
this.writer.endElement(typeRefNs, typeRefPrefix);
} catch (SAXException e) {
Context.getCurrentLogger().warning(
"Cannot write the representation of a statement due to: "
+ e.getMessage());
}
}
@Override
public void startGraph() throws IOException {
this.writer.setPrefix(RDF_SYNTAX, "rdf");
this.writer.setPrefix(RdfConstants.XML_SCHEMA.toString(true, true),
"type");
writer.setDataFormat(true);
writer.setIndentStep(3);
try {
this.writer.startDocument();
this.writer.startElement(RDF_SYNTAX, "RDF");
} catch (SAXException e) {
Context.getCurrentLogger().warning(
"Cannot write the start of the graph: " + e.getMessage());
}
}
@Override
public void startPrefixMapping(String prefix, Reference reference) {
if (prefix == null) {
writer.forceNSDecl(getNamespace(reference.getTargetRef()));
} else {
writer.forceNSDecl(getNamespace(reference.getTargetRef()), prefix);
}
}
/**
* Writes a subject or object node.
*
* @param ref
* The reference of the subject or object node.
* @param subject
* True if the node is the subject of a predicate
* @throws SAXException
*/
private void writeNode(Reference reference, boolean subject)
throws SAXException {
AttributesImpl atts = new AttributesImpl();
if (Link.isBlankRef(reference)) {
atts.addAttribute(RDF_SYNTAX, "NodeId", "rdf:NodeId", "text",
reference.getTargetRef().toString(true, true));
} else {
atts.addAttribute(RDF_SYNTAX, "about", "rdf:about", "text",
reference.getTargetRef().toString(true, true));
}
try {
if (!subject) {
this.writer.emptyElement(RDF_SYNTAX, "Description",
"rdf:Description", atts);
} else {
this.writer.startElement(RDF_SYNTAX, "Description",
"rdf:Description", atts);
}
} catch (SAXException e) {
org.restlet.Context.getCurrentLogger().warning(
"Cannot write the representation of a statement due to: "
+ e.getMessage());
}
}
}