Targeting Domino for Webapps Incidentally

Feb 11, 2020, 5:26 PM

Tags: java maven

I recently had occasion to break ground on a new web project that uses a Notes runtime and has a web front end, and I figured it would be a perfect occasion to structure it in a way that is clean, portable, and, while it will run on Domino, doesn't have to use Tycho.

I ended up coming up with a setup that I'm pretty happy with, and so I put up an example on GitHub for anyone else to use as a reference for similar cases.

What Is This, Specifically?

This is an application that consists of a couple main concepts:

  • Maven for project structure and dependencies
  • Core "plain Java" module that contains code that's intended to be portable and doesn't even know it's in a web app
  • JAX-RS-based REST API
  • Client JS web UI written in Stencil and transpiled with Node
  • Standard webapp project for JEE containers such as Liberty
  • Domino project to wrap the app up as an OSGi bundle

What this is specifically not is an XPages project. And, while it can use a Notes runtime and access NSFs, it's also not something that will be stashed inside an NSF, and the "Notes" part is optional and really only included here to show it's possible. The idea is that this is a standard web app first and a Domino thing second.

Project Structure

The project is organized as a Maven module tree like so:

  • domino-webapp: The parent container project just for configuration
    • core
      • webapp-core: This is the main place for UI-independent business logic
    • web
      • webapp-api-jaxrs: This contains the JAX-RS-based REST API, which exposes the core business logic to the web
      • webapp-webui: This contains a Stencil-based JavaScript app. It doesn't need to be Stencil specifically, or even NPM-based at all, but I find Stencil to be a pretty good choice for this
      • webapp-jee: This is the JEE-container web app, containing very little code of its own and just intended to output a WAR
    • domino
      • webapp-domino: This is the Domino equivalent to the previous project, but contains a chunk of adapter code to get things working, plus some Maven configuration to generate an appropriate OSGi bundle
      • webapp-dist-domino: This is a distribution project that pulls in the Domino OSGi bundle and creates a p2 repository, and then a "site.xml" file for the benefit of importing into an NSF Update Site

How the OSGi Part Works

In going deeper into what's going on, I'm going to start at the end: how to go from a normal web app to a Domino-friendly OSGi bundle. If you're not familiar with what I mean by "web app" in general and in a Domino plugin in particular, it's the sort of thing that Sven Hasselbach wrote a series about a few years back: a Java/Jakarta EE Servlet application using the "WebContainer" extension point in the Domino HTTP runtime.

Traditionally, these projects are built as plain-old Eclipse projects, where you drop a bunch of JARs for your framework of choice into a plug-in project and write your code in there, using Eclipse's Plug-in Development Environment. This works well enough as far as it goes, but puts constraints on how you do development, in particular pretty much requiring Tycho if transitioned to a Maven structure, which would then have massive penalties for the rest of your project.

Fortunately, the thing about an OSGi bundle is that it's really just a JAR file with special metadata, and so it doesn't actually have to be created with a toolchain that has full knowledge of OSGi. As long as the required files end up in the right places inside the JAR (which is in turn just a ZIP file), you're good to go.

In this case, I used the maven-bundle-plugin to decorate the "MANIFEST.MF" file with appropriate OSGi metadata and, importantly, to embed all the compile-scoped project dependencies for me. That second part means that Maven will handle the job of steps 7-10 in Sven's example: it'll bring in the dependencies from Maven, copy them into the right place in the final JAR, and set up the Bundle-ClassPath header to point to them.

It's important to note the "compile-scoped" qualifier there. The Maven projects themselves also depend on a couple things that I know will be present on Domino already, namely IBM Commons, Apache Wink, the Web Container adapter, and Notes.jar. Though it'd probably work if I copied those into the JAR, that would be asking for trouble unnecessarily, so I mark them as "provided" in Maven, and then the bundling process knows to skip over them.

The other OSGi-specific element is the "plugin.xml" file, used by Domino's Equinox framework to identify that the bundle provides a web app. In this case, I put that file in "src/main/resources", where it ends up being copied to the root of the JAR. One down side here is that you have to know ahead of time what the syntax for this file is: since Eclipse won't know this is a plug-in project, you won't get the GUI shown in Sven's example.

There are some other Domino-specific considerations, but I'll return to them later. For now, those parts will cover the OSGi "bridge".

Core: Using the Notes API

The core project doesn't have a lot going on, and that's intentional. It does, though, demonstrate how you can use the JSON-B API for JSON serialization and the Notes API for accessing NSFs and other Notes stuff.

The important parts happen in the project dependencies. The first one is simple: I want to use the JSON-B API, but I was to declare that it will be provided one way or another by the environment. The second one includes Notes.jar by way of my P2 Repository Provider since it's still not available as a normal Maven dependency.

This project contains a single class, which just gathers a bit of information about the runtime environment to be shown as a JSON object. The important part here is my use of NotesThread when calling the Notes API. Since this project can run on non-Domino containers, I can't assume that all threads will already be Notes-friendly, so I use that route. You can also call NotesThread.sinitThread() or go other ways, but I like containing the calls into a separate thread outright in simple cases.

JAX-RS

The JAX-RS project is intended to contain JAX-RS configuration and resource classes, and the immediate part to note is once again the dependency set. Here, I targeted specifically JAX-RS 1.1, which is quite old, but is provided by Apache Wink on all Domino installations. I could theoretically bring in RESTEasy for a newer spec version, but 1.1 is capable enough for now and it keeps things simpler.

In the Application implementation class, I enumerate all of the resource classes used in the app. This is equivalent to the text-file-based method common in Wink apps, but it's portable across JAX-RS implementations and has the side benefit of being compiler-checked. However, though it's a step up from the old Wink way, it's a big step down from the modern JAX-RS way: in newer containers, you can just let the container find your resources by looking for classes with annotations automatically. However, that doesn't fly on Domino and, while you can hack in something roughly equivalent, it's simpler for now to just enumerate the classes explicitly and remember to add them to this list.

There are only two resources here: a Hello World resource and one to ferry the ServerInfo object out using the JAX-RS environment's JSON serializer (more on that in a bit).

The Web UI

The web UI project is complicated, but mostly because NPM-based JavaScript development is complicated. This example uses Stencil, which I quite like, but you can use whatever you'd like: React, Angular, just plain ol' HTML, or whatever.

The important parts here are the use of frontend-maven-plugin to create a Node+NPM environment and build the app and the specific configuration to put the output into "src/main/resources/META-INF/resources". Doing this means that, when this project is wrapped up into a Java-less JAR file, the web resources will be in the "META-INF/resources" directory, which is special on Servlet 3 and above. Any files in there in dependency JARs like this will be visible as if they were in the main web content of your web app.

JEE App

The Jakarta EE app is the simplest of the bunch, and the only actual class in there only exists for example purposes.

The work, such as it is, all happens in the Maven configuration. I declare it to be war-packaged, to not complain if there's no "web.xml" file, to bring in the project dependencies, and to specifically include IBM Commons. It also brings in Notes.jar as a compile-time dependency.

The Domino Shims

Back in the Domino module, it's time to talk about the non-OSGi parts. I've mentioned a few things above that require no configuration in a modern web container, but which will require a bit of legwork in Domino. These are generally related to the fact that Domino's servlet container is version 2.4 and it has no idea about newer standards.

  • I bring in a Eclipse Yasson dependency to provide JSON-B support.
    • To bind that to JAX-RS, I wrote a Provider class that knows how to turn any Java object into JSON when a resource says it wants to output JSON.
    • To register that provider (since it can't be picked up automatically), I subclass the Application class to include it specifically.
  • The ResourcesServlet servlet mimics the Servlet 3 behavior of serving resources out of "META-INF/resources". This specific implementation isn't the best, since it doesn't provide any caching, but it gets the job done and means that the web UI JAR will work the same way on both targets.
  • The RootServlet servlet extends the Wink default REST servlet to shim the ClassLoader around, which avoids a lot of trouble with threads used for web app requests that had previously been used for XPages requests (it's annoying, trust me).
  • I have to include an explicit reference to Wink's JAX-RS provider for some reason to do with bundle class loading.
  • Unlike in the normal web app project, I have to include a "web.xml" file, and this one registers the two servlets above.

Domino Update Site

The second part of the Domino target is the distribution project, which uses the p2-maven-plugin to create a P2 repository. That plugin is a splendid tool for your toolbox and has a lot of capabilities for auto-OSGi-ifying otherwise-non-OSGi projects. In this case, I just want to include the Domino project from the previous step, but I also want to generate an Eclipse feature for it so that it can be imported into an NSF Update Site and with some proper metadata.

I also use the p2sitexml-maven-plugin, which takes the newer-style P2 site generated by the previous step and adds a "site.xml" file, which is needed by the NSF Update Site import process if you want to include categories, which I think are nice.

Seeing It In Action

To run the app on Domino, you can do a Maven install on the root, install the update site from the distribution project onto Domino, and then visit "/exampleapp/". You'll be greeted by a vision of beatuty like this:

Example Webapp Screenshot

Placeholder garishness aside, it shows the Stencil app loading, using the custom favicon, and making a call to the System Info service. That, in turn, shows using the Notes runtime to get the server's distinguished name. It's left as an exercise for the reader to then put in the thousands of hours of work to make a world-class application.

Caveats!

Since this is a Domino thing, there are important caveats.

The first is one I mentioned earlier: because we're restricted to Servlet 2.4/2.5ish, a lot of things just won't work. Indeed, not even all of the 2.4 spec works, as Filters aren't implemented for some reason. Additionally, outside of Servlet and JAX-RS 1.1, you're pretty much in "BYOB" territory when it comes to other JEE specs. In this example, I brought in Yasson for JSON-P and JSON-B and that was pretty simple, but others (say, CDI) would require a lot more fiddly work.

There's also an extra-special caveat when it comes to JSP. Domino's web container knows about JSP, but requires what it calls a "JSP compiler bridge": a special extension that allows for interpreting JSPs inside the special environment it creates. However, it doesn't actually ship with such a bridge. Notes does (and MyFaces too) for what I assume are "social" reasons, but Domino doesn't. You could probably nab the JSP stuff from Notes and drop it onto Domino, but you'd be getting into weird territory. I tried dropping Jasper into the app, but it ran into ClassLoader-casting trouble... hence the bridge, I guess.

Usefulness

Phew! Admittedly, it's a long walk to get to the point where you can just run a web app, and there are quicker ways to get there. However, I do think this is worth it. With this setup, I have a set of Maven projects that work swimmingly in Eclipse and any other Java IDE, a NPM project that acts like any other, and a JEE container front-end for rapid development. No Designer, no NSF syncing, no Plug-in Development Environment, no Tycho. And, though I don't have the full breadth of JEE available to me, JAX-RS is the main one you need for a client-JS app anyway. It's not an appropriate setup for every app, but it's really nice when it fits.

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Slade Swan - Apr 4, 2020, 11:50 AM

Hi Jesse, This is a really interesting write up and I’m trying to follow and keep up. Using techniques like you have described here or outlined in Sven’s blog post do you know if its possible to distribute the Declarative Services plug-ins frustratingly not packaged in Domino? I’m guessing that they need to be installed within the equinox platform proper and not in an add on library/plugin but have no idea where to get information on how to do that if so, or even if not possible/recommended. Any help or reply would be appreciated. Thanks in advance.

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Jesse Gallagher - May 11, 2020, 11:07 AM

I haven't looked into that, but I suspect I will eventually. I did look into adding SPI Fly, which is the same level of "extend the framework" thing, and I had mixed success - the task I took on was large enough that I'm not sure if the trouble was with loading SPI Fly or with any number of other potential factors.

In theory, Domino's OSGi stack is just plain old Neon-era Equinox, and you should be able to do any kind of Provide-Capability thing, and the same should go for adding in a provider for osgi.extender=osgi.component.

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