This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
If the Oracle driver JAR file was not on your class path, I would expect a ClassNotFoundException - not a NoClassDefFoundError. That means that a class that was resolved during compile time (so not using Class.forName) is now missing. It could be that the Oracle driver JAR file is missing a dependency. We need the stack trace to help you further.