Unfortunately I haven't used Java + SLURM yet. With or without DRMAA. At the moment I have access to a Slurm HPC, but we are using Python and have one custom implementation for each batch-scheduler  but with plans to investigate DRMAA.
I think Dask also has custom implementations for each batch-scheduler, and I just had a look at Galaxy and while they have a dramaa runner, they also have a pbs one, and a slurm one...
Couldn't find a good implementation in Java to send you, I am sorry. But in case you learn about one, please share with us :)