Weak reference for MapListeners?

Question

I create objects which implement MapListener and then I register those objects with a CQC. If at some later time the only reference to that object is from the CQC, I would like that object to be garbage collected and the MapListener obviously unregistered. My understanding is that if I create objects and register them as MapListeners, they'll never be GC'd unless I unregister them. Is that right? For my application I'd like the CQC's reference to my MapListener to be a weak reference. Am I correct about all this? Can anyone suggest a work-around for me?
Thanks,
Andrew

Answer 1

Hi Andrew,
CQC (or any of the named cache implementations for that matter) isn't designed to treat listeners weakly, so there really is no clean way of doing what you are asking that I know of. The only thing I can think of is to wrap the other references to your listener object to incorporate a finalizer that will then turn around and unregister the "weak" listener, upon finalization.
For example:
import com.tangosol.net.NamedCache;
import com.tangosol.util.MapEvent;
import com.tangosol.util.MapListener;
import java.util.Iterator;
import java.util.HashSet;
import java.util.Set;
public class MyListener
        implements MapListener
    * The map listener object to wrap.
    * @param listener  the map listener
    public MyListener(MapListener listener)
        m_listenerInternal = listener;
    * Register this listener with the specified cache.
    * @param cache  the named cache to register this listener with
    public void registerWeakListener(NamedCache cache)
        cache.addMapListener(getListenerInternal());
        m_setCache.add(cache);
    // ----- MapListener interface ----------------------------------------
    * {@inheritDoc}
    public void entryInserted(MapEvent evt)
        getListenerInternal().entryInserted(evt);
    * {@inheritDoc}
    public void entryUpdated(MapEvent evt)
        getListenerInternal().entryUpdated(evt);       
    * {@inheritDoc}
    public void entryDeleted(MapEvent evt)
        getListenerInternal().entryDeleted(evt);
    // ----- internal -----------------------------------------------------
    protected MapListener getListenerInternal()
        return m_listenerInternal;
    private MapListener m_listenerInternal;
    private Object      m_finalizer        = new Object()
        public void finalize()
            MapListener listener = m_listenerInternal;
            for (Iterator iter = m_setCache.iterator(); iter.hasNext(); )
                ((NamedCache) iter.next()).removeMapListener(listener);
    private Set         m_setCache         = new HashSet();
    }