Accessing Common functionality from multiple parts of my web app

Question

I have a web app and one of the modules is getting used by other modules in the application.
This was ok when we had 2 modules accessing this module but now we are adding more and more.
The module consists of JSP and Servlets and Backend DAO's.
Right now I have special cases (if statements) that determine what module is accessing this module (each module passes in it id in the URL for example testId, correctionId.
Basically what this module creates can be assoicated with other modules, so the DAO will save and then check to see if certian module ids are present and then does a save based on that.
I dont think this solution is very elegent and I was wondering if anyone had any suggestions on a good way to design this module so it can be easily accessed from other modules in my application.
So to summerize:
All my modules are JSP/Servlet/DAO/Model Code
One of my Modules is accessed from many other modules.
When this module saves its data to the database, it has to take the id that the calling module passsed into it and determine what database bridge table it should save to.
I want to if anyone has any suggestions on how to design this so allowing more modules to access this module will not require anot of extra code in the module.
Thank you,
Al

Answer 1

Hello Al,
Use DAO Pattern.
Have a Factory Class which determines which DAO object it instantiates and hands it over to the Servlet.
Based on the ID, Create the instance object of the DAO and have an interface which has the contract method.
What I mean is :
For Example lets say u have a Interface "ModuleDAO". Have a method "persistData"...
Create 2 DAO Implementations which implement the same Interface and both will have their own "persistData" implementation going to the respective Tables. The reason why I am recommending multiple DAO implementation is to avoid If else / etc and complex coding.The implementations are independant of each other.
Have a DAO Factory [or you can use Spring Framework Bean Factory] infront and have your servlet request for the DAO Implemntation based on the ID.
Your servlet should have NO reference to the Internal Implementation which is being retuirned. It only need to know about the Interface. This way code is clean, decoupled from logic and easier if you want to move the logic out to EJB / External WebServices, etc...
Hope this helps.
By this way, you are exercising all "Factory, DAO and Bridge" Design Patterns.
Thanks,
Pazhanikanthan. P