See Using the Jakarta Commons, Part 3. Lots of cool stuff here, but I'm particularly interested in looking at DBCP, the database connection pool package.

One of my team's apps runs on Tomcat 4.0.x, and we use Tomcat's connection pooling. I'm not sure if it doesn't work how we want it to, or whether we are just using it wrong, but we are having real problems with it. Mainly, the problem is that it seems very keen on throwing connections away. Unless you go to the pool very soon after a connection has been returned, you'll find the pool empty, and have to wait for a new one to be built. Which is, of course, exactly what we are using a pool to avoid. (Note to self - try Evo on Tomcat 4.1.x.)

I also looked into using IBM's AS400JDBCConnectionPool, since it's a '400 that we are trying to get to. But I can't get that going under Tomcat at all.

So, perhaps DBCP is the way to go. Certainly it's worth a look. Unless anyone has any suggestions as to where I'm going wrong with either of the other two approaches?