This object implements the PortletMessage interface and provides the basic functionality needed for sending string messages between portlets on the same page regardless of the portlet application.
Since portlet messaging can be accomplished across portlets in different applications, this is the recommended way to implement portlet messaging.
If you broadcast a DefaultPortletMessage to null, it will be sent to all portlets on the page implementing the MessageListener interface. Example 7-2 illustrates sending a simple broadcast message to all portlets on the same page regardless of application affiliation.
PortletMessage msg = new DefaultPortletMessage("Some ...