I know that’s a lot of work, but I think can be useful a local server running on android device like android-box or android-tv as cheaper server.
Java is a lot more compatible with everything else that is not android or ios. I personally don’t see any advantages in running it on android. You’ll only get into more trouble troubleshooting errors. No, however much I hate Java, I think it’s the correct choice of platform.
You can run Java on the Pi Zero, don’t tell me that is more expensive than an Android box 
@Lichtsignaal I think where running on Android would be VERY useful is if it ran on our Smartphones. Zero cost as we already have them and convenient as it goes everywhere with us.
I rather see the server eliminated all together and have the app serve as it, or at least the possibility to do so. It wouldnt make sense to run something called “server” on a client device.
The android-tv or android-box are very diffused as media player, so it’s probably that any of us have one under the TV.
So why not use it?
Raspberry is cheaper for sure, but isn’t so diffused as android box.
We can use our old smartphone as zero cost battery backup server.