An easy way to do this from the outside would be to create a JVMTI agent, and make currentTimeMillis call into your JNI version. Here's an example in Rust of me

An easy way to do this from the outside would be to create a JVMTI agent, and make currentTimeMillis call into your JNI version. Here's an example in Rust of me doing it for a bit more involved purpose: https://github.com/cretz/stackparam https://github.com/cretz/stackparam. Then people only have to pass your shared lib as a cli arg to get the benefit.