How To Specify main class when using fatjar plugin in gradle.build

Question

I am interested in building a single jar containing all the module dependencies and external jars in a single executable jar file which I will be able to run with java -jar myApp.jar.

I have module A which is dependent on module B. Currently I'm using gradle, and my build.gradlescript looks like this:

    apply plugin: 'fatjar'
    description = "A_Project"
    dependencies {
      compile project(':B_Project')
      compile "com.someExternalDependency::3.0"
    }

When I build it through gradle command: clean build fatjar a fat jar 'A.jar' is created as expected. But running it with as I written above results in: no main manifest attribute, in A.jar How can I modify my build.gradle file and specify the main class, or the manifest?

Answer 1

I have figured it out myself: I've used uberjar Gradle task. now my build.gradle file looks like this:

apply plugin: 'java'
apply plugin: 'application'

mainClassName  = 'com.organization.project.package.mainClassName'

version = '1.0'

task uberjar(type: Jar) {
    from files(sourceSets.main.output.classesDir)
    from {configurations.compile.collect {zipTree(it)}} {
        exclude "META-INF/*.SF"
        exclude "META-INF/*.DSA"
        exclude "META-INF/*.RSA"
}

manifest {
    attributes 'Main-Class': 'com.organization.project.package.mainClassName'
    }
}


dependencies {
compile project(':B_Project')
compile "com.someExternalDependency::3.0"
}

and now I i use it with the command:

clean build uberjar

and it builds one nice runnable jar :)

Answer 2

To get it working using fatjar, I added a manifest section in fatJar task:

task fatJar(type: Jar) {
    baseName = project.name + '-all'
    from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } }
    with jar
    manifest {
        attributes 'Implementation-Title': 'Gradle Quickstart', 'Implementation-Version': version
        attributes 'Main-Class': 'com.organization.project.package.mainClassName'
    }
}