Jar-in-Jar

Jar-in-Jar is a way to load dependencies for mods from within the jars of the mods. To accomplish this, Jar-in-Jar generates a metadata json within META-INF/jarjar/metadata.json on build containing the artifacts to load from within the jar.

Jar-in-Jar is a completely optional system. This will include all dependencies from the jarJar configuration into the jarJar task.

Adding Dependencies

You can add dependencies to be included inside your jar using the jarJar configuration. Jar-in-Jar is a negotiation system, and by default, will create and include the highest version from the prefer version.

// In build.gradle
dependencies {
    // Compiles against and includes the supported version of examplelib
    //   from 2.0 (inclusive)
    jarJar(implementation(group: 'com.example', name: 'examplelib')) {
        version {
            // Version used in your workspace and bundled in mod jar
            prefer '2.0'
        }
    }
}

If your library should only work between an exact version range rather than the preferred version to whatever the highest version there is, you can configure strictly to a range your mod is compatible with:

// In build.gradle
dependencies {
    // Compiles against the highest supported version of examplelib
    //   between 2.0 (inclusive) and 3.0 (exclusive)
    jarJar(implementation(group: 'com.example', name: 'examplelib') {
        version {
            // Sets the supported version of examplelib
            //   between 2.0 (inclusive) and 3.0 (exclusive)
            strictly '[2.0,3.0)'
            // Version used in your workspace and bundled in mod jar
            prefer '2.8.0'
        }
    }
}