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 which can be enabled using jarJar#enable before the minecraft block. This will include all dependencies from the jarJar configuration into the jarJar task. You can configure the task similarly to other jar tasks:

// In build.gradle

// Enable the Jar-in-Jar system for your mod
jarJar.enable()


// Configure the 'jarJar' task
// 'all' is the default classifier
tasks.named('jarJar') {
    // ...
}

Adding Dependencies

You can add dependencies to be included inside your jar using the jarJar configuration. As Jar-in-Jar is a negotiation system, all versions should supply a supported range.

// In build.gradle
dependencies {
    // Compiles against and includes the highest supported version of examplelib
    //   between 2.0 (inclusive) and 3.0 (exclusive)
    jarJar(group: 'com.example', name: 'examplelib', version: '[2.0,3.0)')
}

If you need to specify an exact version to include rather than the highest supported version in the range, you can use jarJar#pin within the dependency closure. In these instances, the artifact version will be used during compile time while the pinned version will be bundled inside the mod jar.

// In build.gradle
dependencies {
    // Compiles against the highest supported version of examplelib
    //   between 2.0 (inclusive) and 3.0 (exclusive)
    jarJar(group: 'com.example', name: 'examplelib', version: '[2.0,3.0)') {
      // Includes examplelib 2.8.0
      jarJar.pin(it, '2.8.0')
    }
}

You can additionally pin a version range while compiling against a specific version instead:

// In build.gradle
dependencies {
    // Compiles against examplelib 2.8.0
    jarJar(group: 'com.example', name: 'examplelib', version: '2.8.0') {
      // Includes the highest supported version of examplelib
      //   between 2.0 (inclusive) and 3.0 (exclusive)
      jarJar.pin(it, '[2.0,3.0)')
    }
}

Using Runtime Dependencies

If you would like to include the runtime dependencies of your mod inside your jar, you can invoke jarJar#fromRuntimeConfiguration within your buildscript. If you decide to use this option, it is highly suggested to include dependency filters; otherwise, every single dependency -- including Minecraft and Forge -- will be bundled in the jar as well. To support more flexible statements, the dependency configuration has been added to the jarJar extension and task. Using this, you can specify patterns to include or exclude from the configuration:

// In build.gradle

// Add runtime dependencies to jar
jarJar.fromRuntimeConfiguration()

// ...

jarJar {
    // Include or exclude dependencies here from runtime configuration
    dependencies {
        // Exclude any dependency which begins with 'com.google.gson.'
        exclude(dependency('com.google.gson.*'))
    }
}

tip

It is generally recommended to set at least one include filter when using #fromRuntimeConfiguration.

Publishing a Jar-in-Jar to Maven

For archival reasons, ForgeGradle supports publishing Jar-in-Jar artifacts to a maven of choice, similar to how the Shadow plugin handles it. In practices, this is not useful or recommended.

// In build.gradle (has 'maven-publish' plugin)

publications {
    mavenJava(MavenPublication) {
        // Add standard java components and Jar-in-Jar artifact
        from components.java
        jarJar.component(it)

        // ...
    }
}