/*
* The contents of this file are subject to the Mozilla Public License
* Version 1.1 (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.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is the Kowari Metadata Store.
*
* The Initial Developer of the Original Code is Plugged In Software Pty
* Ltd (http://www.pisoftware.com, mailto:info@pisoftware.com). Portions
* created by Plugged In Software Pty Ltd are Copyright (C) 2001,2002
* Plugged In Software Pty Ltd. All Rights Reserved.
*
* Contributor(s): N/A.
*
* [NOTE: The text of this Exhibit A may differ slightly from the text
* of the notices in the Source Code files of the Original Code. You
* should use the text of this Exhibit A rather than the text found in the
* Original Code Source Code for Your Modifications.]
*
*/
package org.mulgara.content.rdfxml.writer;
// Java 2 standard packages
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.URI;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import org.apache.log4j.Logger;
import org.apache.xerces.util.EncodingMap;
import org.jrdf.graph.BlankNode;
import org.jrdf.graph.Literal;
import org.jrdf.graph.Node;
import org.jrdf.graph.ObjectNode;
import org.jrdf.graph.SubjectNode;
import org.jrdf.graph.URIReference;
import org.mulgara.query.QueryException;
import org.mulgara.query.TuplesException;
import org.mulgara.query.Variable;
import org.mulgara.resolver.spi.GlobalizeException;
import org.mulgara.resolver.spi.ResolverSession;
import org.mulgara.resolver.spi.Statements;
import org.mulgara.resolver.spi.StatementsWrapperTuples;
import org.mulgara.resolver.spi.TuplesWrapperStatements;
import org.mulgara.store.nodepool.NodePool;
import org.mulgara.store.statement.StatementStore;
import org.mulgara.store.tuples.Tuples;
import org.mulgara.store.tuples.TuplesOperations;
import org.mulgara.util.StringUtil;
/**
* Local space RDFXML writer that generates RDF/XML from Statements and writes
* to a Writer (supports character encoding).
*
* @created 2004-10-21
*
* @author <a href="mailto:robert.turner@tucanatech.com">Robert Turner</a>
*
* @version $Revision: 1.8 $
*
* @modified $Date: 2005/01/05 04:58:03 $
*
* @maintenanceAuthor $Author: newmana $
*
* @company <A href="mailto:info@PIsoftware.com">Plugged In Software</A>
*
* @copyright ©2001 <a href="http://www.pisoftware.com/">Plugged In
* Software Pty Ltd</a>
*
* @licence <a href="{@docRoot}/../../LICENCE">Mozilla Public License v1.1</a>
*/
public class RDFXMLWriter {
/**
* Logger. This is named after the class.
*/
private final static Logger log = Logger.getLogger(RDFXMLWriter.class.getName());
/** Convenience reference to the new line character */
private static final String NEWLINE = System.getProperty("line.separator");
/** Map used to replace namespaces with prefixes */
protected NamespaceMap namespaces = null;
/** Key used by the Namespace Map to represent the RDF namespace */
private String RDF_PREFIX = null;
/** Variables used to convert Statements to Tuples */
private Variable[] vars = null;
/**
* Default Constructor
*/
public RDFXMLWriter() {
vars = new Variable[] {
StatementStore.VARIABLES[0],
StatementStore.VARIABLES[1],
StatementStore.VARIABLES[2],
};
}
/**
* Writes the contents of the JRDF Graph to a Writer in RDF/XML
* format with the encoding specified in the opening XML tag.
*
* @param statements Statements The RDF to be written.
* @param session ResolverSession Used to globalize nodes
* @param writer OutputStreamWriter Destination of the RDF/XML (supports
* character encoding)
* @throws QueryException
*/
synchronized public void write(Statements statements, ResolverSession session,
OutputStreamWriter writer) throws QueryException {
write(statements, session, writer, null);
}
/**
* Writes the contents of the JRDF Graph to a Writer in RDF/XML
* format with the encoding specified in the opening XML tag.
*
* @param statements Statements The RDF to be written.
* @param session ResolverSession Used to globalize nodes
* @param writer OutputStreamWriter Destination of the RDF/XML (supports
* character encoding)
* @param initialPrefixes A set of user-supplied namespace prefix mappings.
* @throws QueryException
*/
synchronized public void write(Statements statements, ResolverSession session,
OutputStreamWriter writer, Map<String,URI> initialPrefixes) throws QueryException {
//validate
if (statements == null) {
throw new IllegalArgumentException("Statements cannot be null.");
}
if (session == null) {
throw new IllegalArgumentException("ResolverSession cannot be null.");
}
if (writer == null) {
throw new IllegalArgumentException("OutputStreamWriter cannot be null.");
}
//write Header, Body and Footer
PrintWriter out = null;
try {
//wrap writer and enable auto flushing
out = new PrintWriter(writer, true);
//ensure statements are writable
statements = prepareStatements(statements);
//initialize the namespaces first
namespaces = new NamespaceMap(statements, session, initialPrefixes);
RDF_PREFIX = namespaces.getRDFPrefix();
//write document
writeHeader(writer);
writeBody(statements, session, out);
writeFooter(out);
} catch (Exception exception) {
log.error("Failed to write Statements.", exception);
throw new QueryException("Failed to write Statements.", exception);
} finally {
if (out != null) out.close();
}
}
/**
* Prepares a Set of Statements for writing.
*
* @param statements Statements
* @throws Exception
* @return Statements
*/
protected Statements prepareStatements(Statements statements) throws Exception {
// Statements may be lazily evaluated. Materializing caches them
Tuples tuples = new StatementsWrapperTuples(statements);
Tuples materializedTuples = TuplesOperations.materialize(tuples);
// ensure variables are in the right order
Tuples projectedTuples = TuplesOperations.project(materializedTuples,
Arrays.asList(vars), true);
materializedTuples.close();
// tuples must be sorted by subject for writing
Tuples sortedTuples = TuplesOperations.sort(projectedTuples);
projectedTuples.close();
return new TuplesWrapperStatements(sortedTuples, StatementStore.VARIABLES[0],
StatementStore.VARIABLES[1], StatementStore.VARIABLES[2]);
}
/**
* Writes the XML Declaration and the opening RDF tag to the print Writer.
* Encoding attribute is specified as the encoding argument.
*
* @param out OutputStreamWriter
* @throws IOException
*/
protected void writeHeader(OutputStreamWriter out) throws IOException {
assert out != null:"OutputStreamWriter is null";
//wrapper for output stream writer (enable autoflushing)
PrintWriter writer = new PrintWriter(out, true);
//get encoding from the Encoding map
String encoding = EncodingMap.getJava2IANAMapping(out.getEncoding());
//only insert encoding if there is a value
if (encoding != null) {
//print opening tags <?xml version="1.0" encoding=*encoding*?>
writer.println("<?xml version=\"1.0\" encoding=\"" + encoding + "\"?>");
}
else {
//print opening tags <?xml version="1.0"?>
writer.println("<?xml version=\"1.0\"?>");
}
//print the Entities
writeXMLEntities(writer);
//print the opening RDF tag (including namespaces)
writeRDFHeader(writer);
}
/**
* Writes the XML Entities (used for namespaces) to the print Writer.
*
* @param out PrintWriter
* @throws IOException
*/
protected void writeXMLEntities(PrintWriter out) throws IOException {
assert out != null:"PrintWriter is null";
//print opening DOCTYPE DECLARATION tag
out.print(NEWLINE + "<!DOCTYPE " + RDF_PREFIX + ":RDF [");
//print namespaces
Set<String> keys = namespaces.keySet();
if (keys != null) {
Iterator<String> keyIter = keys.iterator();
String currentKey = null;
Object currentValue = null;
while (keyIter.hasNext()) {
currentKey = keyIter.next();
currentValue = namespaces.get(currentKey);
if ((currentKey != null) && (currentKey.length() > 0) && (currentValue != null)) {
//write as: <!ENTITY ns 'http://example.org/abc#'>
out.print(NEWLINE + " <!ENTITY " + currentKey + " '" + currentValue + "'>");
}
}
}
//close the opening tag (add a space for readability)
out.print("]>" + NEWLINE + NEWLINE);
}
/**
* Writes the opening RDF tag (with namespaces) to the print Writer.
*
* @param out PrintWriter
* @throws IOException
*/
protected void writeRDFHeader(PrintWriter out) throws IOException {
assert out != null:"PrintWriter is null";
//print opening RDF tag (including namespaces)
out.print("<" + RDF_PREFIX + ":RDF ");
//print namespaces
Set<String> keys = namespaces.keySet();
if (keys != null) {
Iterator<String> keyIter = keys.iterator();
String currentKey = null;
Object currentValue = null;
while (keyIter.hasNext()) {
currentKey = keyIter.next();
currentValue = namespaces.get(currentKey);
if ((currentKey != null) && (currentValue != null)) {
// For default namespace, write 'xmlns="[namespace]"'
// For other namespaces, write 'xmlns:[prefix]="&[prefix];"' (XML entity)
String xmlnsPart = "xmlns";
if (currentKey.length() > 0) {
xmlnsPart += ":" + currentKey;
}
out.print(NEWLINE + " " + xmlnsPart + "=\"" +
((currentKey.length() > 0) ? ("&" + currentKey + ";") : currentValue) + "\"");
}
}
}
//close the opening tag (add a space for readability)
out.print(">" + NEWLINE + NEWLINE);
}
/**
* Writes the Graph's statements as RDF/XML to the print Writer.
*
* @param statements Statements
* @param session ResolverSession
* @param out PrintWriter
* @throws Exception
*/
protected void writeBody(Statements statements, ResolverSession session,
PrintWriter out) throws TuplesException, GlobalizeException, QueryException {
assert statements != null:"Statements is null";
assert session != null:"ResolverSession is null";
assert out != null:"PrinterWriter is null";
//current subject
long subject = NodePool.NONE;
long newSubject = NodePool.NONE;
SubjectNode subjectNode = null;
//write the subjects
statements.beforeFirst();
while (statements.next()) {
newSubject = statements.getSubject();
//has the subject changed?
if (newSubject != subject) {
//close last and open new
if (subject != NodePool.NONE) {
writeClosingSubjectTag(out);
}
subject = newSubject;
subjectNode = (SubjectNode) session.globalize(subject);
//validate
if (subjectNode == null) {
throw new QueryException("subject is null");
}
writeOpeningSubjectTag(subjectNode, out);
}
//get other two nodes and validate
Node predicateNode = session.globalize(statements.getPredicate());
Node objectNode = session.globalize(statements.getObject());
if (predicateNode == null) {
throw new QueryException("predicate is null");
}
if (!(predicateNode instanceof URIReference)) {
throw new QueryException("PredicateNode should be of type: " +
"URIReference, was: " + predicateNode.getClass().getName());
}
if (objectNode == null) {
throw new QueryException("object is null");
}
if (!(objectNode instanceof ObjectNode)) {
throw new QueryException("ObjectNode should be of type: " +
"ObjectNode, was: " + objectNode.getClass().getName());
}
//write the current statement
writeStatement(namespaces, out, subjectNode,
(URIReference) predicateNode, (ObjectNode) objectNode);
}
//write the final closing tag
if (subject != NodePool.NONE) {
writeClosingSubjectTag(out);
}
}
/**
* Creates the appropriate statement Object and calls write on it.
*
* @param namespaces NamespaceMap
* @param writer PrintWriter
* @param subject SubjectNode
* @param predicate PredicateNode
* @param object ObjectNode
* @throws QueryException
*/
protected void writeStatement(NamespaceMap namespaces, PrintWriter writer,
SubjectNode subject, URIReference predicate, ObjectNode object) throws QueryException {
AbstractWritableStatement statement = null;
//type of statement is determined by the object type
if (object instanceof URIReference) {
statement = new URIReferenceWritableStatement(subject, predicate,
(URIReference) object);
} else if (object instanceof BlankNode) {
statement = new BlankNodeWritableStatement(subject, predicate, (BlankNode)object);
} else if (object instanceof Literal) {
statement = new LiteralWritableStatement(subject, predicate, (Literal)object);
} else {
assert(object != null):"Object should not be null";
throw new QueryException("Unknown ObjectNode type: " + object.getClass().getName());
}
assert statement != null : "WritableStatement should not be null";
statement.write(namespaces, writer);
}
/**
* Writes an opening Tag for the subject.
*
* @param subject Node
* @param out PrintWriter
* @throws Exception
*/
protected void writeOpeningSubjectTag(SubjectNode subject, PrintWriter out) {
assert out != null : "PrintWriter is null";
//write
if (subject instanceof URIReference) {
//print as: <rdf:Description rdf:about="http://example.org#subject">
URI uri = ((URIReference) subject).getURI();
String rdf = namespaces.getRDFPrefix();
out.print(" <" + rdf + ":Description " + rdf + ":about=\"" +
uri.toString() + "\">" + NEWLINE);
} else if (subject instanceof BlankNode) {
//get an identifier for the BlankNode
String nodeString = subject.toString();
nodeString = StringUtil.quoteAV(nodeString);
String rdf = namespaces.getRDFPrefix();
//print as: <rdf:Description rdf:nodeID="blankNodeID">
out.print(" <" + rdf + ":Description " + rdf + ":nodeID=\"" +
nodeString + "\">" + NEWLINE);
} else {
throw new IllegalArgumentException("Unknown SubjectNode type: " + subject.getClass().getName());
}
}
/**
* Writes a closing Tag for the subject.
*
* @param out PrintWriter
* @throws Exception
*/
protected void writeClosingSubjectTag(PrintWriter out) {
assert out != null:"PrintWriter is null";
//print as: </rdf:Description>
out.print(" </" + namespaces.getRDFPrefix() + ":Description>" + NEWLINE);
}
/**
* Writes the closing RDF tag to the writer.
*
* @param out PrintWriter
* @throws IOException
*/
protected void writeFooter(PrintWriter out) throws IOException {
assert out != null:"PrintWriter is null";
//print closing RDF tag
out.println("</" + RDF_PREFIX + ":RDF>");
}
}