Kotlin Library Exported As Jar Usable In Java Code, But Not In Kotlin Code

Question

I've written a utility library for a project I am working on in Kotlin. The project has a number of dependencies (such as AWS libraries). I want to package the library as a 'fat' .jar so that I can use the library in other projects without issue.

Currently, I am using the gradle shadow plugin. I am able to successfully use the .jar classes in Java code/projects without issue. However, when using the .jar classes in Kotlin projects/code (or attempting to) I am facing visibility issues (code does not compile b/c of unresolved references). I have no idea what I am doing wrong and am not sure if this is a common issue.

I've already tried:

Gradle Shadow plugin here
Modifying the gradle jar task to include all dependencies myself

The fat jar is successfully created in both cases, and usable in Java code, but Kotlin is not able to resolve the references. However, when I create a non fat jar, the classes are visible, but obviously broken (bc of missing dependencies). So, essentially, only when I create a fat .jar, only my Kotlin code cannot use the library.

Does anyone have any insight?

Does the resulting JAR with Kotlin files also include the META-INF/*.kotlin_module files? These are required for the Kotlin compiler to correctly read the declarations. Without them, you might face visibility issues with top-level declarations. — hotkey
– hotkey, Commented Apr 4, 2019 at 18:48
@hotkey yup, the kotlin_module files are present both in the FAT jar and the original jar — plesh
– plesh, Commented Apr 4, 2019 at 19:18

hotkey · Accepted Answer · 2019-04-04 18:51:19Z

2

Most likely, your re-packaged JAR is missing the META-INF/*.kotlin_module files from the original JARs. These are the Kotlin package metadata files which the Kotlin compiler needs to be able to read top-level declarations from the classes.

If these files are lost, you will face visibility issues with top-level declarations and extensions.

You need to configure your fat JAR tools to also copy these files into the resulting JAR.

answered Apr 4, 2019 at 18:51

hotkey

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3 Comments

plesh Over a year ago

The FAT jar contains the META-INF/*.kotlin_module files. So does the non FAT jar (which is able to be imported and used)

hotkey Over a year ago

@plesh Do you relocate any packages for the fat JAR? The *.kotlin_module files will point the compiler to the original packages, so if the classes are relocated, it will fail to find them.

plesh Over a year ago

I do not. I was previously, but even without relocating packages I run into the same issue.

Pavan · Accepted Answer · 2021-03-29 02:07:15Z

0

You would also need to add both the compile time and run time dependencies when you compile your library jar file.

One way to add them would be for example:

tasks {
    jar{
        from({
            configurations.runtimeClasspath.get().filter { it.name.endsWith("jar") }.map { zipTree(it) }
            configurations.compileClasspath.get().filter { it.name.endsWith("jar") }.map { zipTree(it) }
        })

        exclude ("META-INF/*.RSA", "META-INF/*.SF", "META-INF/*.DSA")
    }
}

answered Mar 29, 2021 at 2:07

Pavan

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