In the introductory post to this series, I started by saying that I've come around to the idea that Java EE (and its kindred technologies) is the future for Java development with Domino, and I think it's worth taking some time to make the case that you should think so too.
A lot of it starts with a nagging question:
Is XPages Dead?
Speaking very strictly, no. XPages remains a component of a commercial product and so bug reports receive attention and fixes as they occur, and presumably all of the many problems the platform is bound to run into as the world evolves will also be addressed.
However, I think the more important question is:
Does It Even Matter If XPages Is Technically Not Dead?
At this point, XPages has, for almost its entire existence inside Domino, been "living" the peculiar kind of undeath that afflicts enterprise software. This is the sort of undeath you could see in, for example, IRIX, which had its last major release in 1998 but was "supported" with maintenance releases for another eight years. XPages has similarly had a few new features since the initial ExtLib release in the 8.5.2 era era - such as the Bootstrap renderkit and some quality-of-life bits - but it's clearly been in maintenance mode for a while. It's been a reactive type of maintenance, too: since XPages doesn't have the Notes-client-app advantage of existing in a controlled environment, XPages development has been increasingly a story of something breaking in some browser and harassing IBM or HCL until there's a fix.
"But wait," you might say, "HCL is going to be in charge now, and look how they're revitalizing the core of Domino! Maybe they'll do the same for XPages!" And, well, maybe they will. I doubt it, though - the core team they brought over isn't involved with XPages, and in general IBM and HCL seem to think so little of it that they don't capitalize it correctly in slides. HCL's development strategy seems to (defensibly) focus on porting the Notes client to other platforms and encouraging developers to either crawl back to LotusScript or to use development stacks that HCL isn't on the hook for, like Node.
And, even if they did staff up to enhance XPages, would it be wise to depend on that? It would still be a single-vendor stack using technologies (OSGi) and idioms (server-side page state) that work but aren't the way the wind is blowing. I would expect that any renewed push would be short-lived.
Okay, Grumpy Gus, Why Is Java EE Any Better?
There was a period in the recent past where Java EE was hitting some similar trouble: Oracle largely lost interest in Java EE (and Java in general, to a lesser extent) and development slowed. However, because so much was open source and (critically) the development pool was so much larger, things kept moving along, with the insurgent group of MicroProfile building new technologies. The transfer of Java EE to Eclipse has proven to be a blessing as well, with the community taking up the mantle splendidly.
As with anything, there's no absolute guarantee of a future path, but JEE has the critical mass that XPages doesn't, with community members and companies emotionally and financially invested in its future. There's no one company whose loss of interest would doom the whole thing, even the Java rump state at Oracle.
And, in the mean time, the technology is just better. You can use current versions of Java, new web technologies are adopted immediately, the IDEs are significantly more stable and featureful, the whole stack has source and Javadoc readily available, the surrounding tooling is better, the modern APIs are simpler and more descriptive, and so forth. Even though XPage's cousin, JSF, has lost some interest, it has evolved significantly past the point where XPages forked away - and is also just one of many good options for app development.
This Is The Bridge We Were Promised
When XPages was ported into Domino, one of the ancillary features for developers was that it would provide a path to the "real" development world, out of our abusive cell of Domino's legacy web stack. It meant being able to consume common Java libraries more practically than in Java agents, extending the capabilities of the platform ourselves, and using development practices that are closer to the rest of the world.
And, to a large extent, these promises came true. We've had the ability to work with the Servlet spec directly, we've been bringing in libraries like Poi with only medium-sized hurdles, and we've been able to (kind of) break the mental binding between the UI and data storage.
Now it's time to truly cross the bridge. There's still a case to be made for writing new XPages applications for now, but every line of XSP markup should be acknowledged as new technical debt. At this point, you should either start working towards Java EE or have a clear plan for how you're going to get there. It doesn't have to be Java EE: there's a lot to be said for taking up HCL on their suggestion to write Node apps, and there are other Java and non-Java frameworks out there that are actively advancing. Regardless of your choice, if you don't choose something, your development will remain stunted and you'll be at a near-guaranteed risk of some critical security problem showing up in an old Dojo version or some other part of the stack and having to clamor for an emergency fix that would otherwise be a one-line pom.xml or package.json tweak (if needed at all).
It's also just very pleasant - give it a try.