POIFSReaderRegistry() 
{
        omnivorousListeners       = new HashSet();
        selectiveListeners        = new HashMap();
        chosenDocumentDescriptors = new HashMap();
}

Construct the registry

 Iterator getListeners(POIFSDocumentPath path,
    String name) 
{
        Set rval               = new HashSet(omnivorousListeners);
        Set selectiveListeners =
            ( Set ) chosenDocumentDescriptors.get(new DocumentDescriptor(path,
                name));
        if (selectiveListeners != null)
        {
            rval.addAll(selectiveListeners);
        }
        return rval.iterator();
}

get am iterator of listeners for a particular document

  void registerListener(POIFSReaderListener listener) 
{
        if (!omnivorousListeners.contains(listener))
        {
            // wasn't already listening for everything, so drop
            // anything listener might have been listening for and
            // then add the listener to the set of omnivorous
            // listeners
            removeSelectiveListener(listener);
            omnivorousListeners.add(listener);
        }
}

register for all documents

  void registerListener(POIFSReaderListener listener,
    POIFSDocumentPath path,
    String documentName) 
{
        if (!omnivorousListeners.contains(listener))
        {
            // not an omnivorous listener (if it was, this method is a
            // no-op)
            Set descriptors = ( Set ) selectiveListeners.get(listener);
            if (descriptors == null)
            {
                // this listener has not registered before
                descriptors = new HashSet();
                selectiveListeners.put(listener, descriptors);
            }
            DocumentDescriptor descriptor = new DocumentDescriptor(path,
                                                documentName);
            if (descriptors.add(descriptor))
            {
                // this listener wasn't already listening for this
                // document -- add the listener to the set of
                // listeners for this document
                Set listeners =
                    ( Set ) chosenDocumentDescriptors.get(descriptor);
                if (listeners == null)
                {
                    // nobody was listening for this document before
                    listeners = new HashSet();
                    chosenDocumentDescriptors.put(descriptor, listeners);
                }
                listeners.add(listener);
            }
        }
}

register a POIFSReaderListener for a particular document