Here is link to the Java toolbox for AS/400 JDBC page. From here, you should be able to answer your questions. I wrote about this stuff in 2002 and I think it is still valid so check www.itjungle.com for articles on the subject. select the AS/400 Guru newsletter and scroll to the bottom (not sure how well the search works) and you will see article on access RPG and the AS/400 from java.
Here is the link to the Java tookbox for java http://www-03.ibm.com/systems/i/software/toolbox/faqjdbc.html
Hope this helps