It be amazing, if batocera have support old java games. On Windows exist KEmulator, on Android J2ME Loader, is it possible to add some of this emulators on Batocera Linux?
KEmulator seems to be windows only.
Libretro has(had?) a core for Java:
Mu/SquirrelJME Dual-Release - December 25, 2018
GitHub - SquirrelJME
SquirrelJME is a Java ME 8 Virtual Machine…..
This project however seems near dead ;( You’d have to find something that is open source and linux. Something that is either already running great or in proper development. ;-) Go and ask questions in Discord