Even though ADF provide lot of declarative way of achieving our goal , There are some instance where you need to write your own code.
Example If I need to write code that is generic to all VO then I will put that code in Application Module Implementation file.
Let us say we need to search employee based on employee id.
I wrote following code in ApplicationModuleImpl and exposed it to be called from user interface. I have given static value for employee but you can make it more generic according to requirement.