When adding a  element to a web application deployment descriptor， the inclusion of which sub-element requires the definition of an error page（）？

A Company.com developer has created a web application that includes a servlet for each use case in the application. These servlets have become rather difficult to maintain because the request processing methods have become very large. There is also common processing code in many servlets because these use cases are very similar. 
Which two design patterns can be used together to refactor and simplify this web application？ （）