/*
* $Header$
* $Revision: 624 $
* $Date: 2006-06-24 21:02:12 +1000 (Sat, 24 Jun 2006) $
*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 2003, 2004 The JRDF Project. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* the JRDF Project (http://jrdf.sf.net/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "The JRDF Project" and "JRDF" must not be used to endorse
* or promote products derived from this software without prior written
* permission. For written permission, please contact
* newmana@users.sourceforge.net.
*
* 5. Products derived from this software may not be called "JRDF"
* nor may "JRDF" appear in their names without prior written
* permission of the JRDF Project.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the JRDF Project. For more
* information on JRDF, please see <http://jrdf.sourceforge.net/>.
*/
package org.jrdf.graph.mem;
import org.jrdf.graph.GraphElementFactory;
import org.jrdf.graph.GraphException;
import org.jrdf.graph.Triple;
import org.jrdf.util.ClosableIterator;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* An iterator that iterates over an entire graph.
* Relies on internal iterators which iterate over all entries in
* the first map, the maps it points to, and the sets they point to.
* The itemIterator is used to indicate the current position.
* It will always be set to return the next value until it reaches
* the end of the graph.
*
* @author <a href="mailto:pgearon@users.sourceforge.net">Paula Gearon</a>
* @author Andrew Newman
*/
public class GraphIterator implements ClosableIterator<Triple> {
/** The iterator for the first index. */
private Iterator<Map.Entry<Long,Map<Long,Set<Long>>>> iterator;
/** The iterator for the second index. */
private Iterator<Map.Entry<Long,Set<Long>>> subIterator;
/** The iterator for the third index. */
private Iterator<Long> itemIterator;
/** The current element for the iterator on the first index. */
private Map.Entry<Long,Map<Long,Set<Long>>> firstEntry;
/** The current element for the iterator on the second index. */
private Map.Entry<Long,Set<Long>> secondEntry;
/** The current subject predicate and object, last returned from next(). Only needed by the remove method. */
private Long[] currentNodes;
/** The nodeFactory used to create the nodes to be returned in the triples. */
private GraphElementFactoryImpl nodeFactory;
/** Handles the removal of nodes */
private GraphHandler handler;
private boolean nextCalled = false;
/**
* Constructor. Sets up the internal iterators.
* @throws IllegalArgumentException Must be created with implementations from
* the memory package.
*/
GraphIterator(Iterator<Map.Entry<Long,Map<Long,Set<Long>>>> newIterator, GraphElementFactory newNodeFactory, GraphHandler newHandler) {
if (!(newNodeFactory instanceof GraphElementFactoryImpl)) {
throw new IllegalArgumentException("Node factory must be a memory implementation");
}
// store the node factory
nodeFactory = (GraphElementFactoryImpl) newNodeFactory;
handler = newHandler;
iterator = newIterator;
}
/**
* Returns true if the iteration has more elements.
* @return <code>true</code> If there is an element to be read.
*/
public boolean hasNext() {
// confirm we still have an item iterator, and that it has data available
return null != itemIterator && itemIterator.hasNext() ||
null != subIterator && subIterator.hasNext() ||
null != iterator && iterator.hasNext();
}
/**
* Returns the next element in the iteration.
*
* @return the next element in the iteration.
* @throws NoSuchElementException iteration has no more elements.
*/
public Triple next() throws NoSuchElementException {
if (null == iterator) throw new NoSuchElementException();
// move to the next position
updatePosition();
if (null == iterator) throw new NoSuchElementException();
nextCalled = true;
// get the next item
Long third = itemIterator.next();
// construct the triple
Long second = secondEntry.getKey();
Long first = firstEntry.getKey();
// get back the nodes for these IDs and uild the triple
currentNodes = new Long[]{first, second, third};
return new TripleImpl((GraphElementFactoryImpl) nodeFactory, first, second, third);
}
/**
* Helper method to move the iterators on to the next position.
* If there is no next position then {@link #itemIterator itemIterator}
* will be set to null, telling {@link #hasNext() hasNext} to return
* <code>false</code>.
*/
private void updatePosition() {
// progress to the next item if needed
if (null == itemIterator || !itemIterator.hasNext()) {
// the current iterator been exhausted
if (null == subIterator || !subIterator.hasNext()) {
// the subiterator has been exhausted
if (!iterator.hasNext()) {
// the main iterator has been exhausted
// tell the iterator to finish
iterator = null;
return;
}
// move on the main iterator
firstEntry = iterator.next();
// now get an iterator to the sub index map
subIterator = firstEntry.getValue().entrySet().iterator();
assert subIterator.hasNext();
}
// get the next entry of the sub index
secondEntry = subIterator.next();
// get an interator to the next set from the sub index
itemIterator = secondEntry.getValue().iterator();
assert itemIterator.hasNext();
}
}
/**
* Implemented for java.util.Iterator.
*/
public void remove() {
if (nextCalled && null != itemIterator) {
itemIterator.remove();
// clean up the current index after the removal
cleanIndex();
// now remove from the other 2 indexes
removeFromNonCurrentIndex();
} else {
throw new IllegalStateException("Next not called or beyond end of data");
}
}
/**
* Checks if a removed item is the last of its type, and removes any associated subindexes if appropriate.
*/
private void cleanIndex() {
// check if a set was cleaned out
Set<Long> subGroup = secondEntry.getValue();
Map<Long,Set<Long>> subIndex = firstEntry.getValue();
if (subGroup.isEmpty()) {
// remove the entry for the set
subIterator.remove();
// check if a subindex was cleaned out
if (subIndex.isEmpty()) {
// remove the subindex
iterator.remove();
}
}
//handler.clean(secondEntry, subIterator, subIndex, );
}
/**
* Helper function for removal. This removes the current statement from the indexes which
* the current iterator is not associated with.
*/
private void removeFromNonCurrentIndex() {
try {
// can instead use var here to determine how to delete, but this is more intuitive
handler.remove(currentNodes);
} catch (GraphException ge) {
IllegalStateException illegalStateException = new IllegalStateException();
illegalStateException.setStackTrace(ge.getStackTrace());
throw illegalStateException;
}
}
/**
* Closes the iterator by freeing any resources that it current holds.
* Nothing to be done for this class.
* @return <code>true</code> indicating success.
*/
public boolean close() {
return true;
}
}