Let's begin our journey of understanding services with a concept that you should be very familiar with as a Java developer--polymorphism. It starts with one interface and (possibly multiple) implementations of that interface. Although interfaces are not strictly necessary for services, they are still a good place to start. Let's say you define a service interface called MyServiceInterface that looks like this:
package service.api;
public interface MyServiceInterface {
public void runService();
}
Now you can have multiple modules containing classes that implement this interface. Since all those modules need access to this interface, let's throw this interface into a module of its own, called service.api, and expose the package that the interface MyServiceInterface is in. Then each implementation module can require...
