/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.directory.server.core.partition.impl.btree.jdbm;
import jdbm.btree.BTree;
import jdbm.helper.Tuple;
import jdbm.helper.TupleBrowser;
import java.util.Comparator;
import org.apache.directory.shared.ldap.cursor.AbstractCursor;
import org.apache.directory.shared.ldap.cursor.InvalidCursorPositionException;
/**
* Cursor over the keys of a JDBM BTree. Obviously does not return duplicate
* keys since JDBM does not natively support multiple values for the same key.
*
* @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
* @version $Rev$, $Date$
*/
public class KeyBTreeCursor<E> extends AbstractCursor<E>
{
private final Tuple tuple = new Tuple();
private final BTree btree;
private final Comparator<E> comparator;
private boolean valueAvailable;
private TupleBrowser browser;
/**
* Creates a Cursor over the keys of a JDBM BTree.
*
* @param btree the JDBM BTree to build a Cursor over
* @param comparator the Comparator used to determine key ordering
* @throws Exception of there are problems accessing the BTree
*/
public KeyBTreeCursor( BTree btree, Comparator<E> comparator ) throws Exception
{
this.btree = btree;
this.comparator = comparator;
}
private void clearValue()
{
tuple.setKey( null );
tuple.setValue( null );
valueAvailable = false;
}
public boolean available()
{
return valueAvailable;
}
public void before( E element ) throws Exception
{
checkNotClosed( "before()" );
browser = btree.browse( element );
clearValue();
}
@SuppressWarnings("unchecked")
public void after( E element ) throws Exception
{
browser = btree.browse( element );
/*
* While the next value is less than or equal to the element keep
* advancing forward to the next item. If we cannot advance any
* further then stop and return. If we find a value greater than
* the element then we stop, backup, and return so subsequent calls
* to getNext() will return a value greater than the element.
*/
while ( browser.getNext( tuple ) )
{
checkNotClosed( "after()" );
E next = ( E ) tuple.getKey();
int nextCompared = comparator.compare( next, element );
if ( nextCompared <= 0 )
{
// just continue
}
else
{
/*
* If we just have values greater than the element argument
* then we are before the first element and must backup to
* before the first element state for the JDBM browser which
* apparently the browser supports.
*/
browser.getPrevious( tuple );
clearValue();
return;
}
}
clearValue();
// just return
}
public void beforeFirst() throws Exception
{
checkNotClosed( "beforeFirst()" );
browser = btree.browse();
clearValue();
}
public void afterLast() throws Exception
{
checkNotClosed( "afterLast()" );
browser = btree.browse( null );
}
public boolean first() throws Exception
{
beforeFirst();
return next();
}
public boolean last() throws Exception
{
afterLast();
return previous();
}
public boolean previous() throws Exception
{
checkNotClosed( "previous()" );
if ( browser == null )
{
browser = btree.browse( null );
}
if ( browser.getPrevious( tuple ) )
{
return valueAvailable = true;
}
else
{
clearValue();
return false;
}
}
public boolean next() throws Exception
{
checkNotClosed( "next()" );
if ( browser == null )
{
browser = btree.browse();
}
if ( browser.getNext( tuple ) )
{
return valueAvailable = true;
}
else
{
clearValue();
return false;
}
}
@SuppressWarnings("unchecked")
public E get() throws Exception
{
checkNotClosed( "get()" );
if ( valueAvailable )
{
return ( E ) tuple.getKey();
}
throw new InvalidCursorPositionException();
}
public boolean isElementReused()
{
return false;
}
}