SpringBoot工程啟動順序與自定義監聽超詳細講解

<!-- bootstrap 啟動器 -->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-bootstrap</artifactId>
</dependency>

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
	this.resourceLoader = resourceLoader;
	Assert.notNull(primarySources, "PrimarySources must not be null");
	this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
	// 初始化web容器型別，預設SERVLET，如果存在org.springframework.web.reactive.DispatcherHandler，則是REACTIVE
	this.webApplicationType = WebApplicationType.deduceFromClasspath();
	this.bootstrapRegistryInitializers = new ArrayList<>(
			getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
	//找到*META-INF/spring.factories*中宣告的所有ApplicationContextInitializer的實現類並將其範例化
	setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
	//找到*META-INF/spring.factories*中宣告的所有ApplicationListener的實現類並將其範例化
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
	//獲得當前執行main方法的類物件
	this.mainApplicationClass = deduceMainApplicationClass();
}

public ConfigurableApplicationContext run(String... args) {
	long startTime = System.nanoTime();
	// 建立bootstrap上下文
	DefaultBootstrapContext bootstrapContext = createBootstrapContext();
	ConfigurableApplicationContext context = null;
	configureHeadlessProperty();
		//通過*SpringFactoriesLoader*檢索*META-INF/spring.factories*，
		//找到宣告的所有SpringApplicationRunListener的實現類並將其範例化，
		//之後逐個呼叫其started()方法，廣播SpringBoot要開始執行了。
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting(bootstrapContext, this.mainApplicationClass);
	try {
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
		//建立並設定當前SpringBoot應用將要使用的Environment（包括設定要使用的PropertySource以及Profile）,
		//並遍歷呼叫所有的SpringApplicationRunListener的environmentPrepared()方法，廣播Environment準備完畢。
		ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
		//決定是否列印Banner
		configureIgnoreBeanInfo(environment);
		Banner printedBanner = printBanner(environment);
		//根據webApplicationType的值來決定建立何種型別的ApplicationContext物件
		//如果是SERVLET環境，則建立AnnotationConfigServletWebServerApplicationContext
		//如果是REACTIVE環境，則建立AnnotationConfigReactiveWebServerApplicationContext
		//否則建立AnnotationConfigApplicationContext
		context = createApplicationContext();
		context.setApplicationStartup(this.applicationStartup);
		//為ApplicationContext載入environment，之後逐個執行ApplicationContextInitializer的initialize()方法來進一步封裝ApplicationContext，
		//並呼叫所有的SpringApplicationRunListener的contextPrepared()方法，【EventPublishingRunListener只提供了一個空的contextPrepared()方法】，
		//之後初始化IoC容器，並呼叫SpringApplicationRunListener的contextLoaded()方法，廣播ApplicationContext的IoC載入完成，
		//這裡就包括通過**@EnableAutoConfiguration**匯入的各種自動設定類。
		prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
		//初始化所有自動設定類，呼叫ApplicationContext的refresh()方法
		refreshContext(context);
		//目前該方法為空
		afterRefresh(context, applicationArguments);
		Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);
		if (this.logStartupInfo) {
			new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);
		}
		//呼叫所有的SpringApplicationRunListener的started()方法，廣播SpringBoot已經完成了ApplicationContext初始化的全部過程。
		listeners.started(context, timeTakenToStartup);
		//遍歷所有註冊的ApplicationRunner和CommandLineRunner，並執行其run()方法。
		//該過程可以理解為是SpringBoot完成ApplicationContext初始化前的最後一步工作，
		//我們可以實現自己的ApplicationRunner或者CommandLineRunner，來對SpringBoot的啟動過程進行擴充套件。
		callRunners(context, applicationArguments);
	}
	catch (Throwable ex) {
		handleRunFailure(context, ex, listeners);
		throw new IllegalStateException(ex);
	}
	try {
		Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);
		listeners.ready(context, timeTakenToReady);
	}
	catch (Throwable ex) {
		handleRunFailure(context, ex, null);
		throw new IllegalStateException(ex);
	}
	return context;
}

public class MyApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
    private final Logger logger = LoggerFactory.getLogger(getClass());
    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        logger.info("MyApplicationContextInitializer, {}", applicationContext.getApplicationName());
    }
}

org.springframework.context.ApplicationContextInitializer=
  com.hsoft.demo.MyApplicationContextInitializer

public static void main(String[] args) {
    SpringApplication springApplication = new SpringApplication(Application.class);
    springApplication.addInitializers(new MyApplicationContextInitializer());
    springApplication.run(args);
}

@Component
public class MyApplicationListener implements ApplicationListener<ApplicationReadyEvent> {
    private final Logger logger = LoggerFactory.getLogger(getClass());
    @Override
    public void onApplicationEvent(ApplicationReadyEvent event) {
        logger.info("MyApplicationListener,{}",event.toString());
    }
}

public static void main(String[] args) {
    SpringApplication springApplication = new SpringApplication(Application.class);
    springApplication.addListeners(new MyApplicationListener());
    springApplication.run(args);
}

@Component
public class MyApplicationRunner implements ApplicationRunner {
    private final Logger logger = LoggerFactory.getLogger(getClass());
    @Override
    public void run(ApplicationArguments args) throws Exception {
        logger.info("MyApplicationRunner, {}",args.getOptionNames());
    }
}

@Component
public class MyCommandLineRunner implements CommandLineRunner {
    private final Logger logger = LoggerFactory.getLogger(getClass());
    @Override
    public void run(String... args) throws Exception {
        logger.info("MyCommandLineRunner, {}", args);
    }
}

/**
 * web容器中進行部署
 *
 */
public class MyServletInitializer extends SpringBootServletInitializer {
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(MyApplication.class);
    }
}