48. SpringApplication.run がやること

// EventsApp.java — run の途中で何がどの順に起きるかを印字する
package l15.events;

import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class EventsApp {
    @Bean CommandLineRunner commandLineRunner() {
        return args -> System.out.println(">> CommandLineRunner.run args=" + java.util.List.of(args));
    }
    @Bean ApplicationRunner applicationRunner() {
        return args -> System.out.println(">> ApplicationRunner.run nonOptionArgs=" + args.getNonOptionArgs());
    }
    public static void main(String[] args) {
        // SpringApplication.run(EventsApp.class, args) を2行に分けて、間にリスナーを挟んだ形
        SpringApplication app = new SpringApplication(EventsApp.class);
        System.out.println(">> webApplicationType = " + app.getWebApplicationType());
        app.addListeners(event -> System.out.println(">> event: " + event.getClass().getSimpleName()));
        ConfigurableApplicationContext ctx = app.run(args);
        System.out.println(">> run() returned: " + ctx.getClass().getSimpleName());
        ctx.close();
    }
}

// Spring Boot 4.1.1 / JDK 25、引数 alpha --flag=1 で起動した出力
// ([log] の行は起動ログ。時刻などを落として短くしてある)
//
// >> webApplicationType = SERVLET
// >> event: ApplicationStartingEvent
// >> event: ApplicationEnvironmentPreparedEvent
// >> event: ApplicationContextInitializedEvent
// [log] Starting EventsApp using Java 25.0.4.1 with PID 1 (...)
// [log] No active profile set, falling back to 1 default profile: "default"
// >> event: ApplicationPreparedEvent
// [log] Tomcat initialized with port 8080 (http)
// [log] Starting service [Tomcat]
// [log] Starting Servlet engine: [Apache Tomcat/11.0.24]
// [log] Root WebApplicationContext: initialization completed in 417 ms
// [log] Tomcat started on port 8080 (http) with context path '/'
// >> event: ServletWebServerInitializedEvent
// >> event: ContextRefreshedEvent
// [log] Started EventsApp in 0.78 seconds (process running for 0.94)
// >> event: ApplicationStartedEvent
// >> event: AvailabilityChangeEvent
// >> CommandLineRunner.run args=[alpha, --flag=1]
// >> ApplicationRunner.run nonOptionArgs=[alpha]
// >> event: ApplicationReadyEvent
// >> event: AvailabilityChangeEvent
// >> run() returned: AnnotationConfigServletWebServerApplicationContext
// (このあとは ctx.close() による終了処理の行)