Hey @sjaak! As you might be already aware, we have our Java API: JCSMP. This new Java API will bring newer feature of the Java language and have it more user-friendly to learn messaging concepts all while allowing a powerful API ! We will be adding more features to the new PubSub+ Message API for Java and aiming for GA in June of this year. I would recommend checking Andrew’s talk in the upcoming global user conference he will be covering more details about the API with a quick demo on how to use it.
Note: this does not mean JCSMP is being deprecated.
Also - great to know about mendix connector!