valuefactoryimpl.java

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/*  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.model.impl;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

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

/**
 * Default implementation of the ValueFactory interface that uses the RDF model
 * classes from this package.
 */
public class ValueFactoryImpl implements ValueFactory {

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

	private int _lastBNodeId;
	private final static String BNODE_PREFIX = "node";
	
	/*-------------------+
	 | Constructors       |
	 +-------------------*/

	/**
	 * Creates a new ValueFactoryImpl.
	 */
	public ValueFactoryImpl() {
		_lastBNodeId = 0;
	}

	/**
	 * Creates a new ValueFactoryImpl that uses the specified document URI to
	 * generate a bNode prefix.
	 * 
	 * @param documentURI A document URI
	 * @see #setDocumentURI
	 */
	public ValueFactoryImpl(String documentURI) {
		this();
		setDocumentURI(documentURI);
	}

	/*-------------------+
	 | Methods            |
	 +-------------------*/

	// Implements ValueFactory.createURI(String)
	public URI createURI(String uri) {
		return new URIImpl(uri);
	}
	
	public URI createURI(String namespace, String localName) {
		return new URIImpl(namespace, localName);
	}

	// Implements ValueFactory.createBNode()
	public BNode createBNode() {
		return new BNodeImpl(BNODE_PREFIX + _lastBNodeId++);
	}
	
	public BNode createBNode(String nodeId) {
		return new BNodeImpl(nodeId);
	}

	// Implements ValueFactory.createLiteral(String)
	public Literal createLiteral(String value) {
		return new LiteralImpl(value);
	}

	// Implements ValueFactory.createLiteral(String, String)
	public Literal createLiteral(String value, String language) {
		return new LiteralImpl(value, language);
	}

	// Implements ValueFactory.createLiteral(String, URI)
	public Literal createLiteral(String value, URI datatype) {
		return new LiteralImpl(value, datatype);
	}

	// Implements ValueFactory.createLiteral(String, String, String)
	public Literal createLiteral(String value, String language, String datatype) {
		if (datatype != null) {
			URI dtURI = createURI(datatype);
			return createLiteral(value, dtURI);
		}
		else if (language != null) {
			return createLiteral(value, language);
		}
		else {
			return createLiteral(value);
		}
	}

	// Implements ValueFactory.createStatement(Resource, URI, Value)
	public Statement createStatement(Resource subject, URI predicate, Value object) {
		return new StatementImpl(subject, predicate, object);
	}

	/**
	 * Sets the URI of the document that is currently being parsed. This URI is
	 * used to generate a 'unique' bNode prefix based on an MD5 (see RFC 1321)
	 * digest of the URI. The result of this digest is practically guaranteed to
	 * be unique.
	 */
	public void setDocumentURI(String uri) {
		MessageDigest messageDigest = null;

		try {
			messageDigest = MessageDigest.getInstance("MD5");
		}
		catch (NoSuchAlgorithmException e) {
			throw new RuntimeException("Unable to get MD5 instance: "
				+ e.getMessage());
		}
		messageDigest.update(uri.getBytes());

		// Create an MD5 digest code (16 bytes)
		byte[] md5code = messageDigest.digest();

		StringBuffer sb = new StringBuffer(32);

		for (int i = 0; i < md5code.length; i++) {
			int b = md5code[i];

			if (b < 0) {
				b += 256;
			}

			String hexString = Integer.toHexString(b).toUpperCase();

			// make sure 2 characters are used for 'hexString'
			if (hexString.length() == 1) {
				sb.append('0');
			}

			sb.append(hexString);
		}

	}

}