For user driven input mapping, you might want to check out Lemur’s InputMapper class.
Here was a demo example:
It has a nicer separation of input and function than InputManager alone does. The latest (soon to be released) version even has the ability to query for all of the current mappings and such. It supports key comobs, treating key-pairs like an axis, etc…
Lemur’s github repo is here:
If you use maven or gradle to build then you can pick up the jar this way:
com.simsilica:lemur:1.6.1
InputMapper’s javadoc:
http://jmonkeyengine-contributions.github.io/Lemur/javadoc/Lemur/com/simsilica/lemur/input/InputMapper.html
There have even been requests to move this class into JME core someday.