Why couldn't this be built inside Q?

Does something like this exist for java, don't want to take the burden of a new language.

I don't think these things really fit the bill, but this is closest I could find. All the codecrafters stuff is focused on reading from a sqlite DB. A great start, but you're not implementing B+ trees.

Hope this gives you some options.

https://github.com/Arminas42/build_your_own_database

https://github.com/search?q=codecrafters+sqlite-java+languag...

it's not that hard, you should try it :)