Use the 'NotificationLifecycleController.doEvents' preference to turn on event processing for a portlet definition.
Example NotificationResult Response Code
Use code like the following -- within another portlet -- to respond to NotificationQuery events and feed items to the NotificationPortlet.
Spring Portlet MVC Controller
@EventMapping(NOTIFICATION_QUERY_QNAME_STRING)
public void echo(final EventRequest req, final EventResponse res) {
final NotificationQuery query = (NotificationQuery) req.getEvent().getValue();
final NotificationEntry entry = new NotificationEntry();
entry.setSource("foo");
entry.setTitle("OMG WOOT!");
final NotificationCategory category = new NotificationCategory();
category.setTitle("MONKEY");
category.setEntries(Arrays.asList(new NotificationEntry[] { entry }));
final NotificationResponse response = new NotificationResponse();
response.setCategories(Arrays.asList(new NotificationCategory[] { category }));
final NotificationResult result = new NotificationResult();
result.setQueryWindowId(query.getQueryWindowId());
result.setResultWindowId(req.getWindowID());
result.setNotificationResponse(response);
res.setEvent(NotificationLifecycleController.NOTIFICATION_RESULT_QNAME, result);
}