Hey all, making a multi-module kotlin gradle appli...

# gradle

[Sangeet Narayan]

Hey all, making a multi-module kotlin gradle application project for the first time. Just made the project structure for now and tried to run it with gradle run but it gave me this error:

Error: Could not find or load main class com.demo.AppKt
Caused by: java.lang.ClassNotFoundException: com.demo.AppKt

Here’s the declaration of main class in my gradle file configuration (will be happy to share the whole file as well):

application {
    mainClassName = "com.demo.AppKt"
}

And here’s my project structure:

demo(root folder)
  -- application(module 1)
    -- src/main/kotlin
          --com.demo
            -- App.kt
    -- build.gradle.kt
  -- login (module 2)
  -- build.gradle.kt
  -- (other build, IDE and gradle folders)

Can anyone tell what error am I doing?

[Vampire]

Best would be to share your whole play project. There are some issues with stuff you mentioned for example but some could also be typos. For example you shouldn't use gradle but the Gradle wrapper, if you are using mainClassName instead of mainClass you are probably using an old Gradle version, the build scripts must end in .gradle.kts, not .gradle.kt

[Sangeet Narayan]

Sure, just a second. https://github.com/sangeetds/isdb
Here it is. Was in a process of testing something but it didn’t work, so the build.gradle.kts file not be as specified above.

[Sangeet Narayan]

And you were right, I was in fact using an older gradle version.

[Vampire]

Yeah, there is no AppKt class anywhere, just as the error says. Btw. setting the main class attribute on the jar is not going to help.

[Sangeet Narayan]

As I said I was working on few things so I changed the names

[Sangeet Narayan]

The right name should be com.demo.DemoApplicationKt right?
Doesn’t work with that too.

[Sangeet Narayan]

Can’t seem to set any main class inside another module. If I bring all the source file outside the module, or if I run ./gradlew run inside the application module, it works

[Sangeet Narayan]

Also, I thought to use something else so I thought to create a jar file and run it, same problem, main class not found

[Vampire]

Your problem is a bit differently.
I had only looked at the root projects build script as you already applied the application plugin there an had there main class set to AppKt.
You have the application plugin applied to your root project and your application project.
So what happens if you do gradlew run is, that all run task in all project are executed.
It starts with :run (the on in the root project) and that fails due to class not found and then the build fails.

If you would have done gradlew --continue run, then after :run failed it would have started :application:run as it does not depend on the failed task.

So if you want to start the run task in the application project specifically, use gradlew application:run, or actually gradlew a:r would be enough in your case.

If you remove the application plugin from the root project, just doing gradlew run is also fine again as then only the application project has a run task.

Or you can of course also apply the application plugin to the root project if you there depend on your application project and use the correct class name.

[Sangeet Narayan]

Sure thanks! Works like a charm. Any general advice so regarding setting up multi modules gradle project from scratch?

[Vampire]

Do it right 😄

[Vampire]

Other than that, the userguide and samples are pretty good generally I'd say

[Vampire]

There are many things to keep in mind so hard to recommend some few points

[Vampire]

A good gradle build of a bigger project is a project of its own actually

[Sangeet Narayan]

Truer words were never spoken

[Sangeet Narayan]

Thanks a lot! Will learn more gradually!