How do I parse command line arguments in Java?

Question

What is a good way of parsing command line arguments in Java?

Answer 1

If you are already using Spring Boot, argument parsing comes out of the box.

If you want to run something after startup, implement the ApplicationRunner interface:

@SpringBootApplication
public class Application implements ApplicationRunner {

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

  @Override
  public void run(ApplicationArguments args) {
    args.containsOption("my-flag-option"); // test if --my-flag-option was set
    args.getOptionValues("my-option");     // returns values of --my-option=value1 --my-option=value2 
    args.getOptionNames();                 // returns a list of all available options
    // do something with your args
  }
}

Your run method will be invoked after the context has started up successfully.

If you need access to the arguments before you fire up your application context, you can just simply parse the application arguments manually:

@SpringBootApplication
public class Application implements ApplicationRunner {

  public static void main(String[] args) {
    ApplicationArguments arguments = new DefaultApplicationArguments(args);
    // do whatever you like with your arguments
    // see above ...
    SpringApplication.run(Application.class, args);
  }

}

And finally, if you need access to your arguments in a bean, just inject the ApplicationArguments:

@Component
public class MyBean {

   @Autowired
   private ApplicationArguments arguments;

   // ...
}