Probably you aren't deploying the oracle driver with your application.
You have several options:
- You can place the driver jars in your
WEB-INF/lib folder
- You export it with your application. -> Right Click on Project ->
Build Path-> Configure Build Path... -> Order and Export -> Check the drivers.
- Place the driver jars in a shared or library extension folder of your application server. (You should go with option one or two though.)
