The helper java class of front controller servlet that makes source code of front controller servlet flexible to modify with out disturbing front controller is called as “Abstract controller”.
This Abstract controller is not a servlet program it is a helper java class for the front controller servlet program / jsp program.
In struts application the predefined java class called “org.apache.struts.action.requestprocessor” class acts as helper class to the front controller Action servlet. That means this class will take care of lots of operations on behalf of ActionServlet.
Similarly this class can also be used to pass addition instructions to ActionServlet.