Running code after Spring Boot starts

Question

It is as simple as this:

@EventListener(ApplicationReadyEvent.class)
public void doSomethingAfterStartup() {
    System.out.println("hello world, I have just started up");
}

Tested on version 1.5.1.RELEASE

Try:

@Configuration
@EnableAutoConfiguration
@ComponentScan
public class Application extends SpringBootServletInitializer {

    @SuppressWarnings("resource")
    public static void main(final String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(Application.class, args);

        context.getBean(Table.class).fillWithTestdata(); // <-- here
    }
}

Have you tried ApplicationReadyEvent?

@Component
public class ApplicationStartup 
implements ApplicationListener<ApplicationReadyEvent> {

  /**
   * This event is executed as late as conceivably possible to indicate that 
   * the application is ready to service requests.
   */
  @Override
  public void onApplicationEvent(final ApplicationReadyEvent event) {

    // here your code ...

    return;
  }
}

Code from: http://blog.netgloo.com/2014/11/13/run-code-at-spring-boot-startup/

This is what the documentation mentions about the startup events:

...

Application events are sent in the following order, as your application runs:

An ApplicationStartedEvent is sent at the start of a run, but before any processing except the registration of listeners and initializers.

An ApplicationEnvironmentPreparedEvent is sent when the Environment to be used in the context is known, but before the context is created.

An ApplicationPreparedEvent is sent just before the refresh is started, but after bean definitions have been loaded.

An ApplicationReadyEvent is sent after the refresh and any related callbacks have been processed to indicate the application is ready to service requests.

An ApplicationFailedEvent is sent if there is an exception on startup.

...

Why not just create a bean that starts your monitor on initialization, something like:

@Component
public class Monitor {
    @Autowired private SomeService service

    @PostConstruct
    public void init(){
        // start your monitoring in here
    }
}

the init method will not be called until any autowiring is done for the bean.

The "Spring Boot" way is to use a CommandLineRunner. Just add beans of that type and you are good to go. In Spring 4.1 (Boot 1.2) there is also a SmartInitializingBean which gets a callback after everything has initialized. And there is SmartLifecycle (from Spring 3).

You can extend a class using ApplicationRunner , override the run() method and add the code there.

import org.springframework.boot.ApplicationRunner;

@Component
public class ServerInitializer implements ApplicationRunner {

    @Override
    public void run(ApplicationArguments applicationArguments) throws Exception {

        //code goes here

    }
}

ApplicationReadyEvent is really only useful if the task you want to perform is not a requirement for correct server operation. Starting an async task to monitor something for changes is a good example.

If, however your server is in a 'not ready' state until the task is completed then it's better to implement SmartInitializingSingleton because you'll get the callback before your REST port has been opened and your server is open for business.

Don't be tempted to use @PostConstruct for tasks that should only happen once ever. You'll get a rude surprise when you notice it being called multiple times...