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.
The primary job of a JDBC driver is to connect to a specific databse server, which has a product specific API. So you need a specific JDBC driver for every database server, eg one for Oracle, one for Microsoft SQL, one for MySQL, etc. So what do you mean by "custom"?