Introduction Portlet Filters

The Java Portlet Specification has introduced concept of Portlet Filters based on Servlet Filters. The basic concept remains the same that Portlet Filter allows you to do some pre and/or post processing for every request. Note one important point that unlike servlets portlet specification defines 4 different phases for handling user request and as result it defines 4 Filter interfaces that you can use.

ACTION_PHASE : If you want to perform filtering during action phase then you should implement class implementing javax.portlet.filter.ActionFilter interface

RENDER_PHASE : If you want to perform filtering during render phase then you should implement class implementing javax.portlet.filter.RenderFilter interface

EVENT_PHASE : If you want to perform filtering during event handling phase then you should implement class implementing javax.portlet.filter.EventFilter interface

RESOURCE_PHASE : If you want to perform filtering during resource serving phase then you should implement class implementing javax.portlet.filter.ResourceFilter interface