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

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'
}
}