Javalin with JPMS and ServiceLoader results in NoClassDefFoundError: kotlin/NoWhenBranchMatchedException

[baumgarb]

Actual behavior (the bug)
Running Javalin with JPMS and ServiceLoader leads to the a NoClassDefFoundError. If I run the very same application not as a module and without the service loader everything works just fine.

Expected behavior
I'm expecting Javalin to work with JPMS and ServiceLoader the same way it does for a console application without Javalin. If you run the console application in the same project everything works out just fine.

To Reproduce

• (✓) Clone no-jpms-and-serviceloader branch and you'll see everything works fine.

• (✓) Run console app in very same project and you'll see everything works fine as well with ServiceLoader and JPMS in place.

  .\gradlew.bat :client:run
  

• (✗) Clone main branch and follow README.md to step 3 and you well end up with the exception:

  > Task :api:run FAILED
  [main] INFO org.example.api.WebAPI - Hello World from WebAPI, yay :-)
  Exception in thread "main" java.lang.NoClassDefFoundError: kotlin/NoWhenBranchMatchedException
          at io.javalin@4.6.4/io.javalin.core.JavalinConfig$Inner.<init>(JavalinConfig.java:77)
          at io.javalin@4.6.4/io.javalin.core.JavalinConfig.<init>(JavalinConfig.java:67)
          at io.javalin@4.6.4/io.javalin.Javalin.<init>(Javalin.java:54)
          at io.javalin@4.6.4/io.javalin.Javalin.create(Javalin.java:91)
          at io.javalin@4.6.4/io.javalin.Javalin.create(Javalin.java:78)
          at org.example.api/org.example.api.WebAPI.main(WebAPI.java:24)
  Caused by: java.lang.ClassNotFoundException: kotlin.NoWhenBranchMatchedException
          at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
          at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
          at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
          ... 6 more
  FAILURE: Build failed with an exception.
  

Additional context
n/a

[tipsy]

@baumgarb java.lang.NoClassDefFoundError: kotlin/NoWhenBranchMatchedException looks like it's more Kotlin related than Javalin related. Have you tried using JPMS with any other Kotlin based JVM project?

[tipsy]

You could check out https://github.com/vihangpatil/kotlin-modules ?

[baumgarb]

@tipsy haven't mixed in any Kotlin based libraries or projects into my Java 9+ Gradle and JPMS projects yet. That's a first and probably you're right.

I'll have a look at https://github.com/vihangpatil/kotlin-modules and let's see if I can figure out something.

Thank you very much either way :-)

[dzikoysk]

Kotlin stdlib supports modules since 1.4+, but Javalin does not export dedicated module-info with library, so in theory it's should work in unnamed module. Because this class cannot be found, you have to find a way to link kotlin stdlib in your project.

[baumgarb]

Issue's solved now, I've pushed a new branch showing how to make it work, see main-solved. If you don't want to bother looking at the latest commit 1f80fc7 of this branch then here's the solution: simply add this line to the module-info.java of the api project:

    requires io.javalin;
    requires com.fasterxml.jackson.databind;
    requires org.slf4j.simple;
    requires kotlin.stdlib;                        <-- simply add this line here

    uses org.example.services.api.PersonReader;

The root cause seems to be that Javalin is not modularized yet. If you look closer into the module resolution (pass --show-module-resolution arg to java) you will see that Javalin is treated as an automatic module and the auto-generated requires statements for this automatic module do not include kotlin.stdlib.

Thanks a lot to @rraumberger who helped me getting to the bottom of this and came up with the solution, but is too shy to post it here :-P

[tipsy]

The root cause seems to be that Javalin is not modularized yet. If you look closer into the module resolution (pass --show-module-resolution arg to java) you will see that Javalin is treated as an automatic module and the auto-generated requires statements for this automatic module do not include kotlin.stdlib.

Do you happen to know what we can do in Javalin to fix this?

Thanks a lot to @rraumberger who helped me getting to the bottom of this and came up with the solution, but is too shy to post it here :-P

He sounds like a great guy!

Issue's solved now, I've pushed a new branch showing how to make it work, see main-solved.

Might make an interesting tutorial for https://javalin.io/tutorials, if you're interested in writing one?

[baumgarb]

Do you happen to know what we can do in Javalin to fix this?

Not off top of my head, I will take a look, maybe there's a quick win we can achieve other than fully introducing modules in the repo.

He sounds like a great guy!

You seem to have a great gut feeling, indeed he is 👍 :-D

Might make an interesting tutorial if you're interested in writing one?

Oh it would be my pleasure, I'd be honored to contribute and I'll definitely do so, thx for offering :-)

[baumgarb]

@tipsy FYI, I've created a PR for adding a tutorial on javalin.io on how to setup a bare bone Gradle project with Javalin & JPMS which also makes use of the new ServiceLoader infrastructure. See PR javalin/website#136.

[tipsy]

@baumgarb that's a really well written tutorial @baumgarb, thank you !

[tipsy]

I'll also close this now :)