How does a Spring Boot console based application work?

If I am developing a rather simple Spring Boot console-based application, I am unsure about the placement of the main execution code. Should I place it in the public static void main(String[] args) method, or have the main application class implement the CommandLineRunner interface and place the code in the run(String... args) method?

I will use an example as the context. Say I have the following [rudimentary] application (coded to interfaces, Spring style):

Application.java

public class Application {

  @Autowired
  private GreeterService greeterService;

  public static void main(String[] args) {
    // ******
    // *** Where do I place the following line of code
    // *** in a Spring Boot version of this application?
    // ******
    System.out.println(greeterService.greet(args));
  }
}

GreeterService.java (interface)

public interface GreeterService {
  String greet(String[] tokens);
}

GreeterServiceImpl.java (implementation class)

@Service
public class GreeterServiceImpl implements GreeterService {
  public String greet(String[] tokens) {

    String defaultMessage = "hello world";

    if (args == null || args.length == 0) {
      return defaultMessage;
    }

    StringBuilder message = new StringBuilder();
    for (String token : tokens) {
      if (token == null) continue;
      message.append(token).append('-');
    }

    return message.length() > 0 ? message.toString() : defaultMessage;
  }
}

The equivalent Spring Boot version of Application.java would be something along the lines: GreeterServiceImpl.java (implementation class)

@EnableAutoConfiguration
public class Application
    // *** Should I bother to implement this interface for this simple app?
    implements CommandLineRunner {

    @Autowired
    private GreeterService greeterService;

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
        System.out.println(greeterService.greet(args)); // here?
    }

    // Only if I implement the CommandLineRunner interface...
    public void run(String... args) throws Exception {
        System.out.println(greeterService.greet(args)); // or here?
    }
}

Solution 1:

You should have a standard loader:

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

and implement a CommandLineRunner interface with @Component annotation

    @Component
    public class MyRunner implements CommandLineRunner {

       @Override    
       public void run(String... args) throws Exception {

      }
   }

@EnableAutoConfiguration will do the usual SpringBoot magic.

UPDATE:

As @jeton suggests the latest Springboot implements a straight:

spring.main.web-application-type=none
spring.main.banner-mode=off

See docs at 72.2

How does a Spring Boot console based application work?

Solution 1:

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