Comment by pkolaczk
Managing off heap memory in Java is pain even worse than manual memory management in C. Unlike C++ and Rust, Java offers no tools for manual memory management, and its idioms like frequent use of exceptions make writing such code extremely error prone.
ByteBuffers and direct memory make it possible.
https://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffe...
But it is a pain and only really useful if you have a big, long lived object. In my case it was loading massive arrays into memory for access by the API server frontend. They needed to be complete overwritten once an hour, and it turns out that allocating 40% of system memory then immediately releasing another 40% back to the GC at once is a good recipe for long pauses or high CPU use