Gradle multi-project build

I have the following project structure:

my-project
 +my-project-data
 +my-project-service
 +my-project-example

Where each of these my-project-data, my-project-service, my-project-examples are defined as sub project to my-project in settings.gradle file. Of course, my-project-services has a dependency to my-project-data. And my-project-examples has a dependencies to my-project-data and my-project service.

In the project my-project-examples I want to have some class with main method and make some queries to DB (Assume that main class is in package com.project.main). Moreover I want to execute this in command line:

java -jar my-project.jar

But to do this I have to set Main-Class attribute. Where do I have to do this in root project build.gradle or somewhere else and what have to be the value of attribute?