I had the following setup in my config/database.yml
development:
adapter: jdbc
driver: oracle.jdbc.driver.OracleDriver
url: jdbc:oracle:thin:@host_name:1530:HOST
username: ...
password: ...
The underscore in url was cosing java.sql.SQLException: No suitable driver
I tried java version 1.5 and 1.6 result was the same until I've inserted IP address and it started to work
Note that underscores in hostnames are typically frowned upon:
http://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_host_names
The URL matching rules may be relying on this fact.