Manifest

manifest adds entries and sections to the MANIFEST.MF of the runnable JAR JavaPackager builds. It has no effect when you bundle your own JAR with runnableJar.

JavaPackager already writes Main-Class and Class-Path (pointing to the libs folder).

Maven

<manifest>
    <additionalEntries>
        <Created-By>Peter</Created-By>
    </additionalEntries>
    <sections>
        <section>
            <name>foo/</name>
            <entries>
                <Implementation-Version>foo1</Implementation-Version>
            </entries>
        </section>
    </sections>
</manifest>

Gradle

javapackager {
    manifest {
        additionalEntries = [
            'Created-By': 'Peter'
        ]
        sections = [
            new io.github.javapackager.model.ManifestSection([
                name: 'foo/',
                entries: [
                    'Implementation-Version': 'foo1'
                ]
            ])
        ]
    }
}

Both produce this MANIFEST.MF, plus the entries JavaPackager writes:

Manifest-Version: 1.0
Created-By: Peter

Name: foo/
Implementation-Version: foo1

Property	Description
additionalEntries	Map of entries added to the main section.
sections	List of named sections, each with a name and a map of entries.