Gradle – FatJar – Could not find or load main class

I reproduced your issue locally.

Just add exclude 'META-INF/*.RSA', 'META-INF/*.SF', 'META-INF/*.DSA' to the jar task.

This will exclude the signatures of interfering dependencies.

Example:

jar {
    manifest {
        attributes "Main-Class": mainClassName
    }

    from {
        configurations.compile.collect { it.isDirectory() ? it : zipTree(it) }
    }
    exclude 'META-INF/*.RSA'
    exclude 'META-INF/*.SF'
    exclude 'META-INF/*.DSA'
}