How to Run Code When a Spring Boot Application Starts

@Bean
ApplicationRunner loadReferenceData(ReferenceDataService service) {
  return args -> service.load();
}

spring.main.banner-mode=off
logging.level.root=WARN

//StartupApp.java
package com.javabrahman.tips.startup;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class StartupApp {

  public static void main(String[] args) {
    SpringApplication.run(StartupApp.class, args);
    System.out.println("main(): SpringApplication.run() has returned");
  }
}

//CacheWarmer.java
package com.javabrahman.tips.startup;

import jakarta.annotation.PostConstruct;
import org.springframework.stereotype.Component;

@Component
public class CacheWarmer {

  @PostConstruct
  void init() {
    System.out.println("1. @PostConstruct        - CacheWarmer is initialized; other beans may not exist yet");
  }
}

//StartupTasks.java
package com.javabrahman.tips.startup;

import java.util.Arrays;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.context.event.ApplicationFailedEvent;
import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.boot.context.event.ApplicationStartedEvent;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.EventListener;
import org.springframework.core.annotation.Order;

@Configuration
public class StartupTasks {

  @EventListener(ApplicationStartedEvent.class)
  void started() {
    System.out.println("2. ApplicationStartedEvent - the context is refreshed; runners have not run yet");
  }

  @Bean
  @Order(1)
  ApplicationRunner loadReferenceData() {
    return args -> {
      System.out.println("3. ApplicationRunner (@Order 1) - option names: " + args.getOptionNames());
      if (args.containsOption("fail-runner")) {
        throw new IllegalStateException("reference data could not be loaded");
      }
    };
  }

  @Bean
  @Order(2)
  CommandLineRunner printArguments() {
    return args -> System.out.println("4. CommandLineRunner (@Order 2) - raw arguments: " + Arrays.toString(args));
  }

  @EventListener(ApplicationReadyEvent.class)
  void ready(ApplicationReadyEvent event) {
    System.out.println("5. ApplicationReadyEvent  - the application is ready");
    if (event.getArgs().length > 0 && event.getArgs()[0].equals("--fail-ready")) {
      throw new IllegalStateException("ready listener failed");
    }
  }

  @EventListener(ApplicationFailedEvent.class)
  void failed(ApplicationFailedEvent event) {
    System.out.println("X. ApplicationFailedEvent - startup failed: " + event.getException().getMessage());
  }
}