Spring Boot: Command Line

A Command Line program within the Spring Boot framework

To write a command line program that works inside the Spring Boot framework, you can use:

import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;


@Component
public class MyCommandLineRunner implements CommandLineRunner {

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

This video shows an example: https://content.pivotal.io/springone-platform-2017/its-a-kind-of-magic-under-the-covers-of-spring-boot-brian-clozel-st%C3%A9phane-nicoll

The @Component annotation is explained here: http://zetcode.com/springboot/component/

Part of the magic of Spring is that you can create a constructor for this class, e.g.

  private final HelloService helloService;
  public MyCommandLineRunner(HelloService helloService) {
    this.helloService = helloService;
  }

And the cool thing is that:

You never actually have to invoke this constructor. It gets automatically invoked by the Spring Boot framework
You never have to invoke the constructor for the HelloService instance either. As long as there is some Bean that Spring knows about that implements HelloService, it will automatically instantiate that Bean and pass the instance into the constructor.

This allows you to change the implementation of HelloService while minimizing the changes to the code.

Spring Boot: Command Line

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