there's some duplication now about DS lookup but the first one is generic for all specs while the username is strictly Derby adapter specific code make sure we always close the obtained DB connection (not just on errors) as jndi DS will be pooled most likely
when jdbc is being configured do not raise if there's a :driver_instance instead of the :driver
instead use Tomcat's JNDI impl ... jars get auto-downloaded
these will be tagged as "jdbc-mysql-x.x.x"
- for MS SQL we have the jTDS 1.3.0 JDBC driver - for Postgres we now recommend the 9.2 driver - for Derby we shall allow to package latest (10.9.1) driver