n3writer.java

这是外国一个开源推理机

/*  Sesame - Storage and Querying architecture for RDF and RDF Schema
 *  Copyright (C) 2001-2005 Aduna
 *
 *  Contact: 
 *  	Aduna
 *  	Prinses Julianaplein 14 b
 *  	3817 CS Amersfoort
 *  	The Netherlands
 *  	tel. [phone]
 *  	fax. [phone]
 *
 *  	http://aduna.biz/
 *  	http://www.openrdf.org/
 *  
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package org.openrdf.rio.n3;

import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.openrdf.util.StringUtil;

import org.openrdf.model.BNode;
import org.openrdf.model.Literal;
import org.openrdf.model.Resource;
import org.openrdf.model.URI;
import org.openrdf.model.Value;

import org.openrdf.rio.RdfDocumentWriter;
import org.openrdf.rio.ntriples.NTriplesUtil;

/**
 * An implementation of the RdfDocumentWriter interface that writes RDF
 * documents in N3 format.
 * <p>
 * <em>Note: due to lack of any clear documentation on N3, it is not known
 * whether the output adheres for 100% to the N3 format.</em>
 **/
public class N3Writer implements RdfDocumentWriter {

/*---------------------------------+
| Variables                        |
+---------------------------------*/

	private Writer _out;

	private Map _namespaceTable;

	private boolean _writingStarted;

	private Resource _lastWrittenSubject;

/*---------------------------------+
| Constructors                     |
+---------------------------------*/

	/**
	 * Creates a new N3Writer that will write to the supplied OutputStream.
	 * 
	 * @param out The OutputStream to write the N3 document to.
	 **/
	public N3Writer(OutputStream out) {
		this( new OutputStreamWriter(out) );
	}

	/**
	 * Creates a new N3Writer that will write to the supplied Writer.
	 * 
	 * @param out The Writer to write the N3 document to.
	 **/
	public N3Writer(Writer out) {
		_out = out;
		_namespaceTable = new HashMap();
		_writingStarted = false;

		_lastWrittenSubject = null;
	}

/*---------------------------------+
| Methods from interface RdfWriter |
+---------------------------------*/

	public void setNamespace(String prefix, String name)
		throws IOException
	{
		// setNamespace should not overwrite existing namespace mappings
		if (!_namespaceTable.containsKey(name)) {
			_namespaceTable.put(name, prefix);
			
			if (_writingStarted) {
				if (_lastWrittenSubject != null) {
					// The last statement still has to be closed:
					_out.write(".");
					_writeNewLine();
					
					_lastWrittenSubject = null;
				}
				
				_writeNamespace(prefix, name);
				_writeNewLine();
			}
		}
	}

	public void startDocument()
		throws IOException
	{
		_writingStarted = true;

		// Write namespace declarations

		Iterator nameIterator = _namespaceTable.keySet().iterator();
		while (nameIterator.hasNext()) {
			String name = (String)nameIterator.next();
			String prefix = (String)_namespaceTable.get(name);

			_writeNamespace(prefix, name);
			_writeNewLine();
		}

		_writeNewLine();
	}

	public void endDocument()
		throws IOException
	{
		if (_lastWrittenSubject != null) {
			// The last statement still has to be closed:
			_out.write(".");
			_lastWrittenSubject = null;
		}

		_out.flush();

		_writingStarted = false;
	}

	public void writeStatement(Resource subj, URI pred, Value obj)
		throws IOException
	{
		if (!_writingStarted) {
			throw new RuntimeException("Writing has not yet started");
		}

		// SUBJECT
		if (subj.equals(_lastWrittenSubject)) {
			_out.write(";");
			_writeNewLine();
			_writeIndent();
		}
		else {
			if (_lastWrittenSubject != null) {
				// The previous statement still has to be closed:
				_out.write(".");
				_writeNewLine();
			}

			// Write new subject:
			_writeNewLine();
			_writeResource(subj);

			_lastWrittenSubject = subj;
		}

		// PREDICATE
		_writeURI(pred);

		// OBJECT
		if (obj instanceof Resource) {
			_writeResource( (Resource)obj );
		}
		else if (obj instanceof Literal) {
			_writeLiteral( (Literal)obj );
		}

		// Don't close the line just yet. Maybe the next statement
		// has the same subject.
	}

	public void writeComment(String comment)
		throws IOException
	{
		if (_lastWrittenSubject != null) {
			// The last statement still has to be closed:
			_out.write(".");
			_writeNewLine();

			_lastWrittenSubject = null;
		}

		_out.write("# ");
		_out.write(comment);
		_writeNewLine();
	}

/*---------------------------------+
| Other methods                    |
+---------------------------------*/

	private void _writeNamespace(String prefix, String name)
		throws IOException
	{
		_out.write("@prefix ");
		_out.write(prefix);
		_out.write(": <");
		_out.write(name);
		_out.write("> .");
	}

	private void _writeResource(Resource res)
		throws IOException
	{
		if (res instanceof BNode) {
			_writeBNode((BNode)res);
		}
		else {
			_writeURI((URI)res);
		}
	}

	private void _writeURI(URI uri)
		throws IOException
	{
		String namespace = uri.getNamespace();
		String prefix = (String)_namespaceTable.get(namespace);

		if (prefix == null) {
			_out.write("<");
			_out.write(namespace);
			_out.write(uri.getLocalName());
			_out.write("> ");
		}
		else {
			_out.write(prefix);
			_out.write(":");
			_out.write(uri.getLocalName());
			_out.write(" ");
		}
	}

	private void _writeBNode(BNode bNode)
		throws IOException
	{
		// FIXME: N3 has no concept of named bNodes
		_out.write("() ");
	}

	private void _writeLiteral(Literal lit)
		throws IOException
	{
		// Do some character escaping on the label:
		// FIXME: not nice to be dependent on class NTriplesUtil
		String s = lit.getLabel();
		s = NTriplesUtil.escapeString(s);
		s = StringUtil.gsub("'", "\\'", s);

		_out.write("\"");
		_out.write(s);
		_out.write("\"");

		// Write the literal's language if it has any:
		if (lit.getLanguage() != null) {
			_out.write("-");
			_out.write(lit.getLanguage());
		}

		_out.write(" ");
	}

	private void _writeIndent()
		throws IOException
	{
		_out.write("\t");
	}

	private void _writeNewLine()
		throws IOException
	{
		_out.write("\n");
	}
}