Apache Derby is an embeddable SQL database implemented as a Java Jar file.
There are many such technologies around these days, but I still think Derby is perhaps the most mature.
I haven't the time or inclination to explain all of the features and benefits of Derby, you can visit the website. But Derby is perhaps most useful in it's simplest form, which is as a read only embedded JAR that simply contains data, accessible by SQL at runtime.
Of course Derby doesn't have to be read only.
Here is an example Ant task you can use to create a (read only) Derby database jar you can then use in your application. Of course you can just take the relevant code out of this if you want to create a Maven goal etc.
And here is an example POJO (actually an injectable (IoC) spring bean) you can use to read from that database at runtime.