What is the official spring boot way to start a simple non web based java application?

Simply use the ApplicationContext that SpringApplication.run returns and then work with that. That's pretty much all that is required

public static void main(String[] args) {
    ApplicationContext context = SpringApplication.run(Application.class, args);
    HelloSpring bean = context.getBean(HelloSpring.class);
    bean.printHello();
}

So you can open a gui, etc. and use the ApplicationContext to get your beans, etc.

From the docs: http://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#boot-features-command-line-runner

Application.class

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

HelloSpring.class

@Component
public class HelloSpring implements CommandLineRunner {
    @Override
    public void run(String... args) {
        this.printHello();
    }

    public void printHello() {
        System.out.println("Hello Spring!");
    }
}

You can even make it so the run() method actually prints out you message but this way keeps it closer to your intent where you have implemented a method and want it executed when the application starts.