Where to go for Java DB Questions
While Java DB is Sun's distribution of Apache Derby, we do not maintain a separate users' forum for it outside of the Apache Derby users' forum.
So, the best place to post your Java DB questions is still the Apache Derby users' alias: derby-user.
The range of questions posed and answered there are truly fantastic, and interesting, some showing a great freshness of users.
Here's a recent sample (and wherever you see Derby, you can easily substitute "Java DB"):