SoftReferenceList.java

/*******************************************************************************
 * This file is part of OpenNMS(R).
 *
 * Copyright (C) 2007-2011 The OpenNMS Group, Inc.
 * OpenNMS(R) is Copyright (C) 1999-2011 The OpenNMS Group, Inc.
 *
 * OpenNMS(R) is a registered trademark of The OpenNMS Group, Inc.
 *
 * OpenNMS(R) is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published
 * by the Free Software Foundation, either version 3 of the License,
 * or (at your option) any later version.
 *
 * OpenNMS(R) 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with OpenNMS(R).  If not, see:
 *      http://www.gnu.org/licenses/
 *
 * For more information contact:
 *     OpenNMS(R) Licensing <license@opennms.org>
 *     http://www.opennms.org/
 *     http://www.opennms.com/
 *******************************************************************************/

package org.opennms.netmgt.correlation;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.util.AbstractSequentialList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Set;

/**
 * <p>SoftReferenceList class.</p>
 *
 * @author <a href="mailto:brozow@opennms.org">Mathew Brozowski</a>
 * @version $Id: $
 */
public class SoftReferenceList<T> extends AbstractSequentialList<T> {
	
	private final List<SoftReference<T>> m_contents = new LinkedList<SoftReference<T>>();
	private final ReferenceQueue<T> queue = new ReferenceQueue<T>();

	/** {@inheritDoc} */
	@Override
	public ListIterator<T> listIterator(final int index) {
		processQueue();
		return new SoftReferenceListIterator<T>(m_contents.listIterator(index), queue);
	}
	
	/**
	 * <p>removeCollected</p>
	 */
	public void removeCollected() {
		processQueue();
		for (final Iterator<SoftReference<T>> iter = m_contents.iterator(); iter.hasNext();) {
			final SoftReference<T> ref = iter.next();
			if (ref.get() == null) {
				iter.remove();
			}
		}
	}
	
	private void processQueue() {
		final Set<Reference<? extends T>> removed = new HashSet<Reference<? extends T>>();
		Reference<? extends T> ref;
		while((ref = queue.poll()) != null) {
			removed.add(ref);
		}
		m_contents.removeAll(removed);
	}

	/** {@inheritDoc} */
	@Override
	public int size() {
		processQueue();
		return m_contents.size();
	}
	
	private static class SoftReferenceListIterator<E> implements ListIterator<E> {
		final ListIterator<SoftReference<E>> m_it;
		final ReferenceQueue<E> m_queue;
		
		public SoftReferenceListIterator(final ListIterator<SoftReference<E>> it, final ReferenceQueue<E> queue) {
			m_it = it;
			m_queue = queue;
		}

		public void add(final E o) {
			assertNotNull(o);
			m_it.add(createRef(o));
		}

		public boolean hasNext() {
			return m_it.hasNext();
		}

		public boolean hasPrevious() {
			return m_it.hasPrevious();
		}

		public E next() {
			final SoftReference<E> ref = m_it.next();
			return ref.get();
		}

		public int nextIndex() {
			return m_it.nextIndex();
		}

		public E previous() {
			final SoftReference<E> ref = m_it.previous();
			return ref.get();
		}

		public int previousIndex() {
			return m_it.previousIndex();
		}

		public void remove() {
			m_it.remove();
		}

		public void set(final E o) {
			assertNotNull(o);
			m_it.set(createRef(o));
		}

		private SoftReference<E> createRef(final E element) {
			return new SoftReference<E>(element, m_queue);
		}
		
		private void assertNotNull(final E o) {
			if (o == null) {
				throw new NullPointerException("null cannot be added to SoftReferenceLists");
			}
		}
		
		
	}


}