com.numdata.oss.ui.BackgroundProcessingListModel Maven / Gradle / Ivy
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/*
* Copyright (c) 2017, Numdata BV, The Netherlands.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * 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.
* * Neither the name of Numdata nor the
* names of its contributors may be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
* ANY EXPRESS 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 NUMDATA BV 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.
*/
package com.numdata.oss.ui;
import java.util.*;
import java.util.concurrent.*;
import javax.swing.*;
import com.numdata.oss.*;
/**
* List model that automatically processes elements in the background. A typical
* application would be retrieving additional data for list elements, like
* database records, files, or images.
*
* The {@link #process} method must be implemented to perform the background
* task for each element. It will be called automatically from a background
* thread one data is added to the model. The {@link #processed} and {@link
* #done} methods can be overridden to handle processed elements on the Event
* Dispatch Thread, typically to update the user interface.
*
* NOTE: Elements that have been retrieved more recently are processed with
* higher priority. This is intended to improve the user experience when the
* model is used for a {@link javax.swing.JList}, in which case visible items
* are processed first.
*
* @param type of elements in this model.
*
* @author Peter S. Heijnen
*/
public abstract class BackgroundProcessingListModel
extends ArrayListModel
{
/**
* Queue of elements to fetch.
*/
private final transient Queue> _queue = new LinkedHashList>();
/**
* Worker that processes the queue in the background.
*/
private transient QueueWorker _worker;
/**
* Serialized data version.
*/
private static final long serialVersionUID = 306770265034722112L;
/**
* Construct model.
*/
protected BackgroundProcessingListModel()
{
_worker = null;
}
/**
* Executed on background worker thread to process elements.
*
* @param element Element to process.
*/
protected abstract void process( T element );
/**
* Executed on the Event Dispatch Thread for elements that were
* previously processed by the {@link #process} method. The argument is
* a list, because multiple elements may have been processed before this
* method is called. These elements will be coalesced.
The default
* implementation fires list update events for elements that (still) exist
* in the list model.
*
* @param elements Elements that were processed.
* @param progress Queue progress percentage (0-100).
*
* @see SwingWorker#process(List)
*/
protected void processed( final List elements, final int progress )
{
int start = -1;
int end = -3;
/*
* NOTE: 'end = -2' won't work, because then 'end + 1' is -1, which is
* a possible return value of 'indexOf' (i.e. item not found),
* resulting in an event with negative indices.
*/
for ( final T element : elements )
{
final int index = indexOf( element );
if ( index >= 0 )
{
if ( index == end + 1 )
{
end = index;
if ( start == -1 )
{
start = index;
}
}
else
{
if ( start <= end )
{
fireContentsChanged( start, end );
}
start = index;
end = index;
}
}
}
if ( start <= end )
{
fireContentsChanged( start, end );
}
}
/**
* Executed on the Event Dispatch Thread after all elements in the
* queue have been processed.
*
* @param elements Elements that were processed .
* @param cancelled Whether the background process was cancelled or not.
*
* @see SwingWorker#done
*/
protected void done( final List elements, final boolean cancelled )
{
_worker = null;
final boolean empty;
synchronized ( _queue )
{
empty = _queue.isEmpty();
}
if ( !empty )
{
final QueueWorker worker = new QueueWorker();
_worker = worker;
worker.execute();
}
}
/**
* Returns the element at the specified position in this list.
*
* This re-queues elements to give them top priority.
*
* @inheritdoc
*/
@Override
public T get( final int index )
{
synchronized ( _queue )
{
final T result = super.get( index );
if ( result != null )
{
final QueueElement queueElement = new QueueElement( result );
if ( _queue.remove( queueElement ) ) /* only requeue if it's queued */
{
addToQueue( queueElement );
}
}
return result;
}
}
/*
* Override methods that change the contents of the model to update the queue.
*/
@Override
public boolean add( final T element )
{
synchronized ( _queue )
{
if ( element != null )
{
addToQueue( new QueueElement( element ) );
}
return super.add( element );
}
}
@Override
public void add( final int index, final T element )
{
synchronized ( _queue )
{
if ( element != null )
{
addToQueue( new QueueElement( element ) );
}
super.add( index, element );
}
}
@Override
public boolean addAll( final Collection collection )
{
synchronized ( _queue )
{
for ( final T element : collection )
{
if ( element != null )
{
final QueueElement queueElement = new QueueElement( element );
_queue.remove( queueElement );
addToQueue( queueElement );
}
}
return super.addAll( collection );
}
}
@Override
public boolean addAll( final int index, final Collection collection )
{
synchronized ( _queue )
{
for ( final T element : collection )
{
if ( element != null )
{
final QueueElement queueElement = new QueueElement( element );
_queue.remove( queueElement );
addToQueue( queueElement );
}
}
return super.addAll( index, collection );
}
}
@Override
public void clear()
{
synchronized ( _queue )
{
_queue.clear();
super.clear();
}
}
@Override
public T remove( final int index )
{
synchronized ( _queue )
{
final T result = super.remove( index );
if ( ( result != null ) && !contains( result ) )
{
_queue.remove( new QueueElement( result ) );
}
return result;
}
}
@Override
public void removeRange( final int fromIndex, final int toIndex )
{
synchronized ( _queue )
{
final int modCount = toIndex - fromIndex;
final Object[] removedElements = new Object[ modCount ];
for ( int i = 0; i < removedElements.length; i++ )
{
removedElements[ i ] = super.get( fromIndex + i );
}
super.removeRange( fromIndex, toIndex );
for ( final Object element : removedElements )
{
if ( ( element != null ) && !contains( element ) )
{
_queue.remove( new QueueElement( (T)element ) );
}
}
}
}
@Override
public T set( final int index, final T element )
{
synchronized ( _queue )
{
final T result = super.set( index, element );
if ( result != element )
{
if ( ( result != null ) && !contains( result ) )
{
_queue.remove( new QueueElement( result ) );
}
if ( element != null )
{
final QueueElement queueElement = new QueueElement( element );
_queue.remove( queueElement );
addToQueue( queueElement );
}
}
return result;
}
}
@Override
protected void finalize()
throws Throwable
{
_queue.clear();
final QueueWorker worker = _worker;
if ( worker != null )
{
_worker = null;
worker.cancel( true );
}
clear();
super.finalize();
}
/**
* This method is called internally to add new elements to the queue. It
* will automatically start a {@link QueueWorker} to process the queue.
*
* @param queueElement Element to add to queue.
*/
private void addToQueue( final QueueElement queueElement )
{
synchronized ( _queue )
{
_queue.add( queueElement );
}
if ( _worker == null )
{
final QueueWorker worker = new QueueWorker();
_worker = worker;
worker.execute();
}
}
/**
* Worker that processes the queue in this model.
*/
public class QueueWorker
extends SwingWorker, T>
{
@Override
protected List doInBackground()
{
final ArrayList result = new ArrayList();
setProgress( 0 );
QueueElement queueElement;
while ( !isCancelled() )
{
synchronized ( _queue )
{
queueElement = _queue.poll();
}
if ( queueElement == null )
{
break;
}
final T element = queueElement.element;
if ( !result.contains( element ) )
{
BackgroundProcessingListModel.this.process( element );
for ( Iterator i = result.iterator(); i.hasNext(); )
{
if ( !contains( i.next() ) )
{
i.remove();
}
}
if ( contains( element ) )
{
result.add( element );
final int progress;
synchronized ( _queue )
{
progress = ( 100 * result.size() ) / ( result.size() + _queue.size() );
}
setProgress( progress );
publish( element );
}
}
}
return result;
}
@Override
protected void process( final List elements )
{
processed( elements, getProgress() );
}
@Override
protected void done()
{
try
{
BackgroundProcessingListModel.this.done( get(), isCancelled() );
}
catch ( InterruptedException e )
{
e.printStackTrace();
}
catch ( ExecutionException e )
{
e.printStackTrace();
}
}
}
/**
* This class is used to wrap list elements in the queue.
*
* @param type of element.
*/
static class QueueElement
implements Comparable>
{
/**
* List element.
*/
T element;
/**
* Value of {@link System#nanoTime()} when last accessed.
*/
long time;
/**
* Construct new queue element.
*
* @param element Element to queue.
*/
QueueElement( final T element )
{
this.element = element;
time = System.nanoTime();
}
public int hashCode()
{
return ( element != null ) ? element.hashCode() : 0;
}
public boolean equals( final Object other )
{
final boolean result;
final T element = this.element;
if ( other == this )
{
result = true;
}
else if ( other instanceof QueueElement )
{
final T otherElement = ( (QueueElement)other ).element;
result = ( element == null ) ? ( otherElement == null ) : element.equals( otherElement );
}
else
{
result = false;
}
return result;
}
@Override
public int compareTo( final QueueElement other )
{
return ( time > other.time ) ? -1 : 1;
}
}
}