What, you mean like a startup action when the portlet is started at container startup?
Servlet.service.events.pre is invoked before every service event, that includes every action, render, resource, etc., event.
Otherwise you can use spring bean initializers if you're using spring, heck even class constructors can achieve the same. Portlet classes also have init() methods so you can extend whatever portlet class you're currently using and override it's init() method to add your own initialization for the portlet.
All of these break down if you're talking about running this once for each portlet instance, though, so I don't know how to truly answer your question without more context.
