Using Eclipse, there are several plugins to generate JPA entities from an existing database. I would add Dali to those listed by Arun.
AFAIK, these tools will produce a one-shot reverse of your database. If your need is to reverse a changing database using bottom-up strategy, you'll have to be careful to any change you add manually to the generated entities: they will be lost each time you reverse the schema.
Did you specify the driver information, the exact URL with schema details, userId and password?
May be the userId and password which you're using to login doesn't have access to the required schema.
Can you post some screenshot and what errors are you getting?
If you are not laughing at yourself, then you just didn't get the joke.