IBM DB2 11.1 is freely available for development.
There are many editions, but I recommend IBM Db2 Developer-C that is full featured and compatible with the commercial offering. There are some limitations of database size and memory usage, but it should be more than enough for development.
If you want to download only the DB2 JDBC drivers see:
Learning to code products doesn't take as long as you think - more precisely, 300 hours to learn, build, and launch. Learn about the history and misconceptions of development preventing you from even starting and then hop on that tech bus.