creating an in-memory hsqldb instance for using hibernate in a maven build

a simple setup for testing

Lately I've been working on some Hibernate examples I plan on sharing soon, and I wanted to create a simple in memory instance of HSQLDB to test against. Trying to drill down to the bare necessities of what I needed proved to be a little scattered across several resources, so I thought I'd aggregate everything in one place.

This article is assuming a few things:

• You're using a Maven build
• You're using Hibernate
• You don't care about persisting to disk or database state

creating the server

Setting up the server is mostly straightforward, but I do have a subtle change to make the Maven aspect easier:

Note that the location is set to target/mem:test. This tells HSQLDB to create an in-memory only database, which will never persist changes to disk. That said, HSQLDB still writes out a few files (a log, script, and properties file) which uses the name of the database. Prefixing the name with target/ will write to Maven's default build directory so that your workspace doesn't have a bunch of log data in it that you'll have to ignore from version control

configuring hibernate

Now that we can fire up the database, we can connect to it via Hibernate. The config file below will connect, but also has a subtlety similar to what was used above:

Here's where things get a little screwy, and there's a decent chance it's because I don't understand certain aspects of HSQLDB. In this case, the connection string is target/hsql:mem:test. As far as I can tell, both the HSQLDB server and driver write to the same set of files, prefixed by the connection string or database name. When you start up the database and connection pool, you end up with files in target with the names of mem:test.* and hsql:mem:test.*. Since both of these sets of files end up being written to, I figure it's not a bad thing that they're named differently. I do find it a little odd that the client logs data like this, but at least at the moment I don't care enough to see if this can be adjusted. If it can be I'll update this post to reflect how to do that.

wrapping up...

As stated above, I really wanted a sandbox to demonstrate a few Hibernate interactions with, so I really wanted to keep the setup as barebones as possible. There are probably certain things I could or should have configured differently, but the above will work to get you going. I never really use HSQLDB, so if you're reading this article and have some input on a better way to do this or any corrections that should be made, please leave your feedback in the comments :)