Migrating a Large XPages App to Jakarta EE 9

Jan 6, 2022, 7:44 PM

  1. Updating The XPages JEE Support Project To Jakarta EE 9, A Travelogue
  2. JSP and MVC Support in the XPages JEE Project
  3. Migrating a Large XPages App to Jakarta EE 9
  4. XPages Jakarta EE Support 2.2.0
  5. DQL, QueryResultsProcessor, and JNoSQL
  6. Implementing a Basic JNoSQL Driver for Domino
  7. Video Series On The XPages Jakarta EE Project
  8. JSF in the XPages Jakarta EE Support Project
  9. So Why Jakarta?

Last month, I moved my XPages Jakarta EE project to JEE 9, which involved the large hurdle of switching package names from javax.* to jakarta.*. That was all well and good for the project and opened the door to further improvements, but it's one thing to do it in a support library and another to move an actual large project over.

So I set my sights on my workhorse client project, the one with the sprawling OSGi bundle set and complicated XPages project, which I have running regularly on both Domino and Open Liberty. Over the last few days, I did the porting work and came out successful, and I think it ended up being another tale worth telling.

There are two main topics when it comes to this project: why and how.

Why

Now, why are we gonna do this? I mean, the app is running fine as it is, and the immediate goal of the switch is to keep it functionally the same. Why is it worth going through this hassle for an active project?

There are a few reasons.

The first and biggest is that the jakarta.* switch isn't going to go backwards. There is never going to be a feature update for any of the javax.* versions of the JEE specs, and so staying on that version is stagnation. While we can do what we want to do today, that won't hold true tomorrow unless we make the move. Since that's inevitable, it meant that every new line of javax.* code is technical debt, and the sooner you can stop creating that, the better.

The second reason is that, while the Jakarta EE spec move from 8 to 9 retained the same functionality, we actually gained technical improvements in the switch.

One technical gain was very immediate: the version of RESTEasy I had put into the XPages JEE project previously was a couple major versions old now, and this let me bump it up to the latest.

Another technical gain had to do with the nightmare that is dealing with OSGi dependencies on Domino. Due to the lack of proper versioning of standard specs in the XPages stack, the increasingly-corrupt classpath, and the bundling of specs with utility libraries, I've always had to lose a lot of time dealing with manually tweaking OSGi imports and dependencies. While this move doesn't eliminate all of it, it removes a lot. Terror packages like javax.mail and javax.activation can now be left behind in favor of jakarta.mail and jakarta.activation without worry of conflicting imports from the XPages libraries and the ndext classpath directory. The move to JEE 9 resulted in a significant reduction in such code and configuration.

And finally, it's going to help bring in new features we haven't introduced yet but will benefit from. For example, I have my eye on the MicroProfile REST client, which makes consuming REST services in a clear and type-safe way a dream. While it's possible that I'd be able to add that in earlier versions, the switch to jakarta.* will remove huge tasks from my plate entirely.

How

So now that I'd convinced myself that it's a good idea, the only remaining problem was actually doing it. Fortunately, I already solved most of it in the XPages JEE project itself. Moreover, the way I'd solved things there allowed me to remove extra dependencies that kind of "double-solved" the problem in this specific app, things like making sure that javax.inject was compatible between that project and the other third-party dependencies we use.

One of the big things that was different between the XPages JEE project on its own and this app was the way this runs across multiple platforms.

Historically, the fact that Liberty was running Servlet 4 and Domino was running Servlet 2.4/2.5 didn't come much into play. The newer versions of the javax.servlet classes were entirely compatible with the old ones: XPages could consume a Servlet 4 HttpServletRequest without issue and would just ignore the new methods added. Now, though, I had to do some shimming in two directions.

Domino, since I don't control the lowest layers, would remain a Servlet 2.5-ish container natively, while for Liberty I would move to a true Servlet 5 container. Since both the XPages markup and app code must remain the same, that meant a double emulation setup:

Diagram of the Domino and Liberty Stacks

In these diagrams, "JEE 9 App" represents the app's use of Jakarta standards other than XPages: CDI, JAX-RS, JSON-B, and so forth.

The first part of this work took place in the XPages Jakarta EE project. There, I created wrapper versions of all pertinent javax.servlet/jakarta.servlet classes going both from "old to new" and "new to old". Most of these classes are just direct delegations, but some parts involve either throwing exceptions for trying to use new features on an old stack, emulating new behavior on top of the old, or quietly not supporting some capabilities. These classes get me most of the way. When I need to move in one direction or the other, I call the appropriate method from ServletUtil and it takes care of the differences. This project also handled a lot of fiddly details to do with things like the JavaMail to Jakarta Mail switch, so I could just bring that in too and not worry about it.

That handled some distinctions. The next big one was to use this to make sure XPages can survive in a Servlet 5 world. The good news here is that it was simpler than I thought it would be. XPages only has a few actual entrypoints - there's a Servlet to handle global resources (the URLs involving /xsp/.ibm* and the like), another to handle actual XPages *.xsp requests, and maybe one or two others I'm not thinking of. As long as you can handle those URLs and send a legacy javax.servlet object to the closed-source code, the stack will take it from there: things like externalContext.getRequest() will return the wrapped object you passed in in the first place, and don't try to do any weird magic to fetch the request object from the container or anything.

Previously, I had Servlets that extended the stock ones like DesignerFacesServlet directly, but this had to change. Fortunately, it's a simple matter of delegation. Instead of subclassing the original ones, now I create an instance internally and pass along incoming requests to that, appropriately dumbing down the Servlet 5 objects to 2.5-level ones. I was able to do this with fewer functional changes than one might think and put it into new versions of the XPages Runtime project.

Beyond those big-ticket items, there were a few cases where I had to take care to appropriately handle knowing when my code was going to receive a javax.servlet object or a jakarta.servlet one, but otherwise there wasn't much to do beyond updating dependencies and a find-and-replace on class imports. None of the XSP markup changed, very little of the in-NSF code changed, and the only large in-app code changes I made were to remove workarounds that were no longer needed.

Conclusion

All in all, I'd say this went better than I'd expected. There's naturally still room for trouble (it's not in production yet, for one), but overall I feel that this bore out my intent in making the move in the first place.

It's also an interesting case study in the way my XPages Jakarta EE and Open Liberty Runtime projects conceptually interact. They both approach the same ideal from different directions: write open-standards-based applications that make use of Domino data. With this move to JEE 9, the addition of new specs to the XPages JEE project, and the shedding of (some) old limitations, they're converging all the more. More code can be directly shared between the two app types, and the code that isn't shared unmodified can at least be written all the more similarly. JAX-RS is the in-common way to do REST services; CDI is the in-common way to do managed beans; OpenAPI annotations are an in-common way to document services. These are technologies that have wide support with multiple implementations and, crucially, are open standards. XPages was one step towards a non-proprietary stack, and this is several more.

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