You'll need to provide a lot more information if you expect anyone to be
able to help you.

At the very least, you should provide the full stack trace of the
exception, plus an excerpt from the configuration file for your servlet
container where you specify the database connection parameters, and the
Java code which your servlet uses to establish the database connection.

You should also indicate whether your database server and the servlet
container live on the same machine, or on different machines, and tell
us whether you are able to connect to your database using a simple Java
test program i.e. without all the additional complexity of the servlet
container and JNDI.

David Harper
Cambridge, England