/*
* 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.client.jrdf.util;
// Log4J
import org.apache.log4j.Logger;
// JRDF
import org.jrdf.graph.*;
import org.mulgara.client.jrdf.*;
import org.mulgara.client.jrdf.exception.*;
/**
* A Non-scalable ClosableIteratorProxy that returns Triples with an Unique
* SubjectNode. Calling next will return the next Triple with an Unique
* SubjectNode (Predicate and Object Nodes will be null).
*
* @created 2004-08-16
*
* @author <a href="mailto:robert.turner@tucanatech.com">Robert Turner</a>
*
* @version $Revision: 1.8 $
*
* @modified $Date: 2005/01/05 04:57:37 $
*
* @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 UniqueSubjectIterator
implements VirtualClosableIteratorProxy<Triple> {
/**
* Logger. This is named after the class.
*/
@SuppressWarnings("unused")
private final static Logger log = Logger.getLogger(UniqueSubjectIterator.class.getName());
/** Needs to be closed when this Iterator is closed */
private OrderedClosableIteratorProxy<Triple> proxy = null;
/** Pre-cached "next" triple with an Unique SubjectNode */
private Triple nextTriple = null;
/** Node used to determine if the Subject is different */
private SubjectNode currentSubject = null;
/** Builder used to create Triples */
private GraphElementBuilder builder = null;
/** Indicates that the Iterator has already been closed */
private boolean closed = false;
/**
* Default Constructor.
*
* @param proxy OrderedClosableIteratorProxy
* @throws GraphException
*/
public UniqueSubjectIterator(OrderedClosableIteratorProxy<Triple> proxy) throws
GraphException {
super();
//validate
if (proxy == null) {
throw new IllegalArgumentException("OrderedClosableIteratorProxy cannot be null.");
}
//initialize members
this.proxy = proxy;
this.builder = new GraphElementBuilder();
//cach the first unique triple
try {
this.getNext();
} catch (GraphElementFactoryException factoryException) {
throw new GraphException("Could not retrieve first Triple.", factoryException);
}
}
/**
* Closes the ClosableIteratorProxy used to create this Iterator.
*
* @return boolean
*/
public boolean close() {
//the proxy is now closed
this.closed = true;
//close the data source
return this.proxy.close();
}
/**
* Returns <tt>true</tt> if the iteration has more elements. (In other
* words, returns <tt>true</tt> if <tt>next</tt> would return an element
* rather than throwing an exception.)
*
* @return <tt>true</tt> if the iterator has more elements.
*/
public boolean hasNext() {
//ensure the iterator is not closed
if (this.closed) {
throw new IllegalStateException("ClosableIterator has been closed.");
}
//nextTriple will be null when no more unique SubjectNodes are found
return (this.nextTriple != null);
}
/**
* Returns the next Triple in the iteration and caches the next Triple
* containing an unique SubjectNode.
*
* @return the next element in the iteration.
* @exception NoSuchElementException iteration has no more elements.
* @exception JRDFClientException Cannot retrieve next Triple.
*/
public Triple next() {
//ensure the iterator is not closed
if (this.closed) {
throw new IllegalStateException("ClosableIterator has been closed.");
}
//reference to "Old" nextTriple (getNext() modifies state of nextTriple)
Triple triple = this.nextTriple;
//cache get the next triple
try {
this.getNext();
} catch (GraphElementFactoryException factoryException) {
throw new JRDFClientException("Could not get next value.", factoryException);
}
return triple;
}
/**
* Let the proxy do it.
*
* @exception UnsupportedOperationException if the <tt>remove</tt>
* operation is not supported by this Iterator.
*/
public void remove() {
//ensure the iterator is not closed
if (this.closed) {
throw new IllegalStateException("ClosableIterator has been closed.");
}
this.proxy.remove();
}
/**
* Gets the next Triple with an unique SubjectNode from the proxy.
*
* @throws GraphElementFactoryException
*/
private void getNext() throws GraphElementFactoryException {
//reset old value
this.nextTriple = null;
//current triple being evaluated
Triple proxyTriple = null;
while (this.proxy.hasNext()) {
proxyTriple = (Triple) this.proxy.next();
//is the Subject new?
if (this.newSubject(proxyTriple)) {
//create new Triple
this.currentSubject = proxyTriple.getSubject();
this.nextTriple = this.builder.createTriple(this.currentSubject, null, null);
//stop looking
break;
}
}
}
/**
* Compares the triple's SubjectNode to the current SubjectNode. Returns
* true if the SubjectNode's are different.
*
* @param triple Triple
* @return boolean
*/
private boolean newSubject(Triple triple) {
//validate
if (triple == null) {
throw new IllegalArgumentException("Triple cannot be null.");
}
if (triple.getSubject() == null) {
throw new IllegalArgumentException("Triple returned a null SubjectNode.");
}
//compare subjects
return !triple.getSubject().equals(this.currentSubject);
}
}