[mumblemumble]

The problem I've run into with mrjars is that they tend to break libraries that do a bunch of classpath scanning. Mrjars add some stuff to the classpath that the older tools didn't understand and would choke on.

It's one of those things I would personally argue is a naughty hack that should be avoided if at all possible, but it's also something that's historically been ubiquitous within the Java ecosystem. It's frequently how convention-over-configuration dependency injection (as found in Spring Boot or Jersey) tends to be done, for example.