I keep coming back to java.util.ServiceLoader. I have used it to put a JSON layer behind a contract, so the core code carries no direct dependency on any particular JSON library, and I can swap the implementation without touching callers. The same shape works for JWT handling, where the concrete library might be jose4j or another JOSE implementation, and you can easily find other decoupling use-cases.

A long long (long?) time ago, I wrote a post about the ServiceLoader. In short, the Service Loader allows to separate an API and its implementations in different JARs. The client code depends on the API only, while at runtime, the implementation(s) that is (are) on the classpath will be used. This is great way to decouple the client code from the implementing one.