unfortunately i "don't speak" java but i've heard about steemj which written in java to interact with the blockchain. it's not updated since a while, tho.
receiving blocks and checking for comments should be simple and does not require a huge server.
you might want to join SteemDevs Discord channel where you can find help if you need.
anyway, keep up with the good work :)
Thanks for the support.
I use steemj, with modifications.
https://github.com/muksihs/steem-java-api-wrapper