FYI - Because JAR files are specially formatted ZIP files, you can also prepend a shell script stub to the front of the file. Java reads JAR files and doesn't start processing them until it sees the ZIP magic bytes (PK\x03\x04). So long as your shell script doesn't contain those bytes, you can add whatever you want.
This is about the minimal stub script you can get away with.
#!/bin/bash
exec java -jar $0 "$@"
exit 1
But inside a container (with its own mount namespace) or inside a chroot then the qemu binaries does not necessarily exist. But the binfmt_misc handler will still work in this case because of two features.
1. The kernel will open the qemu binaries in the original mount namespace when the binfmt_misc handler is registered with the F-flag (Fix binary) so the kernel will always have an open file reference to the qemu binary independent of mount namespace.
2. Distributions (at least Debian) ships statically linked qemu binaries so that qemu does not need to load any shared libraries inside the target namespace/chroot.