<!-- 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容器類型，默認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*中聲明的所有ApplicationContextInitializer的實現(xiàn)類并將其實例化
	setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
	//找到*META-INF/spring.factories*中聲明的所有ApplicationListener的實現(xiàn)類并將其實例化
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
	//獲得當前執(zhí)行main方法的類對象
	this.mainApplicationClass = deduceMainApplicationClass();
}

public ConfigurableApplicationContext run(String... args) {
	long startTime = System.nanoTime();
	// 創(chuàng)建bootstrap上下文
	DefaultBootstrapContext bootstrapContext = createBootstrapContext();
	ConfigurableApplicationContext context = null;
	configureHeadlessProperty();
		//通過*SpringFactoriesLoader*檢索*META-INF/spring.factories*，
		//找到聲明的所有SpringApplicationRunListener的實現(xiàn)類并將其實例化，
		//之后逐個調(diào)用其started()方法，廣播SpringBoot要開始執(zhí)行了。
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting(bootstrapContext, this.mainApplicationClass);
	try {
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
		//創(chuàng)建并配置當前SpringBoot應(yīng)用將要使用的Environment（包括配置要使用的PropertySource以及Profile）,
		//并遍歷調(diào)用所有的SpringApplicationRunListener的environmentPrepared()方法，廣播Environment準備完畢。
		ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
		//決定是否打印Banner
		configureIgnoreBeanInfo(environment);
		Banner printedBanner = printBanner(environment);
		//根據(jù)webApplicationType的值來決定創(chuàng)建何種類型的ApplicationContext對象
		//如果是SERVLET環(huán)境，則創(chuàng)建AnnotationConfigServletWebServerApplicationContext
		//如果是REACTIVE環(huán)境，則創(chuàng)建AnnotationConfigReactiveWebServerApplicationContext
		//否則創(chuàng)建AnnotationConfigApplicationContext
		context = createApplicationContext();
		context.setApplicationStartup(this.applicationStartup);
		//為ApplicationContext加載environment，之后逐個執(zhí)行ApplicationContextInitializer的initialize()方法來進一步封裝ApplicationContext，
		//并調(diào)用所有的SpringApplicationRunListener的contextPrepared()方法，【EventPublishingRunListener只提供了一個空的contextPrepared()方法】，
		//之后初始化IoC容器，并調(diào)用SpringApplicationRunListener的contextLoaded()方法，廣播ApplicationContext的IoC加載完成，
		//這里就包括通過**@EnableAutoConfiguration**導(dǎo)入的各種自動配置類。
		prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
		//初始化所有自動配置類，調(diào)用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);
		}
		//調(diào)用所有的SpringApplicationRunListener的started()方法，廣播SpringBoot已經(jīng)完成了ApplicationContext初始化的全部過程。
		listeners.started(context, timeTakenToStartup);
		//遍歷所有注冊的ApplicationRunner和CommandLineRunner，并執(zhí)行其run()方法。
		//該過程可以理解為是SpringBoot完成ApplicationContext初始化前的最后一步工作，
		//我們可以實現(xiàn)自己的ApplicationRunner或者CommandLineRunner，來對SpringBoot的啟動過程進行擴展。
		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);
    }
}