Publishing and Processing Events

To define an event, you would have to declare it in portlet.xml

This code defines an event named cf:HelloEvent, where cf refers to the namespace and HelloEvent is the local name. Its type is defined by the <value-type> tag. These event definitions require you to use qname to uniquely identify the event.

Now add the events to specific portlets, which are either going to publish (generate) an event or process (consume) an event. You add this information to portlet.xml as well.
<supported-publishing-event> tag is used to publish an event.