What is this?

This plugin rolls up your current project's jar, resources, and all of its dependencies into a self-contained archive with only the minimal set of class and resource files necessary to the project. It collects all the parameters based on reasonable defaults from the project and forks off a process to run Autojar with these collected values.

What is Autojar?

Here's a description of what Autojar does from the project page:

Autojar creates jar archives of minimal size from different sources (classes,
directories, libraries). Starting from one or more classes, it scans the
bytecode recursively for other classes, extracts them from their archives if
necessary, and adds them to the output file. The resulting archive contains only
classes that are really needed. Thus the size and loading time of applets can be
kept low, and applications can be made self-contained.

You can read more about Autojar here.

Examples

At a minimum, you only need to supply your project's main class and the gradle-autojar plugin will take care of the rest by using it as the starting point for running the Autojar process:

apply plugin: 'gradle-autojar'

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.github.rholder:gradle-autojar:1.0.1'
    }
}

task myAwesomeFunJar(type: Autojar) {
    mainClass = 'com.foo.Foo'
}

Other available parameters for customizing the behavior:

task myAwesomeFunJar(type: Autojar) {
    mainClass = 'com.foo.Foo'

    // manifest closure works just like the Jar task
    manifest {
        attributes('Created-By':'Gradle Autojar')
    }

    // resource files must be manually added, resolved from the classpath for inclusion
    autojarFiles = ['foo.txt', 'dir/foo2.txt']

    // additional classes can be manually added when they're not included automatically
    autojarClasses = ['org.apache.commons.lang.time.DateUtils']

    // override the defaults of -ba
    autojarExtra = '-bav'
}

You probably don't need this

This plugin is designed to output a minimized executable artifact. It is extraordinarily bad to use on a large, complicated project with only minimal or ad-hoc test coverage of the final deliverable. I wouldn't recommend using this for anything that resembles a regular deployment where development is ongoing or release cycles that are dependent on other upstream pieces of software that are outside of the original developers' control are involved. The consequences of missing a critical class that's only loaded during runtime usually isn't worth the tradeoff of a smaller final artifact size. There are better ways of rolling up a single artifact that can guarantee that all runtime dependencies stay intact (see FatJAR and One-JAR).

Fine, when SHOULD I use this?

If you have a standalone utility that depends on only a limited subset of large and unwieldy libraries (like fastutil or the AWS SDK for Java) then this might be a reasonable artifact packaging solution.

License

The gradle-autojar build plugin is released under version 2.0 of the Apache License. This plugin comes bundled with an unmodified release of Autojar, which is licensed under the terms set forth by the GPLv2. In compliance with the use of GPLv2 licensed software, gradle-autojar only utilizes a fork and exec mechanism for running an unmodified Autojar process whereby derived arguments are passed from the plugin. The original source code for Autojar can be found here.