Portlet events contain information about an event to which a portlet might need to respond. Action events are generated when an HTTP request is received by the portlet container that is associated with an action, such as when the user clicks a link or submits a form.
Portlet actions can be one of two types:
PortletAction objects: The PortletAction object has been deprecated in favor of simple portlet action strings. It is maintained in the Portlet API to support existing portlets that use PortletActions. You should always use simple portlet actions instead of PortletAction objects.
Simple portlet action Strings: Actions created as simple actions can be executed multiple times, enabling a user’s back button to work. Links ...