springBoot启动配置原理

几个重要的的事件回调机制
配置在META-INF/spring.factories中
ApplicationContextInitializer
SpringApplicationRunListener
放在ioc容器中
ApplicationRunner
CommandLineRunner

创建SpringApplication对象

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
		this.resourceLoader = resourceLoader;
		Assert.notNull(primarySources, "PrimarySources must not be null");
		//保存主配置类
		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
		//判断当前应用是否是一个web应用
		this.webApplicationType = WebApplicationType.deduceFromClasspath();
		//从类路径下找到META-INF/spring.factories配置的所有ApplicationContextInitializer；然后保存起来
		setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
		//从类路径下找到META-INF/spring.factories配置的所有ApplicationListener；然后保存起来
		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
		//从多个配置类中找到有main方法的主配置类
		this.mainApplicationClass = deduceMainApplicationClass();
	}

运行run方法

public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();

		//获取SpringApplicationRunListeners；从类路径下META-INF/spring.factories
		SpringApplicationRunListeners listeners = getRunListeners(args);
		//回调所有获取的SpringApplicationRunListeners的starting()方法
		listeners.starting();
		try {
			//封装命令行参数
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
			//准备环境
			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
			//创建环境完成后回调SpringApplicationRunListeners 的environmentPrepared()方法；表示环境准备完成
			
			//得到系统属性spring.beaninfo.ignore，如果为空设置为true
			configureIgnoreBeanInfo(environment);
			//打印banner
			Banner printedBanner = printBanner(environment);
			//创建ApplicationContext；决定创建web的ioc还是普通的ioc
			context = createApplicationContext();
			//出现异常时用来做分析报告
			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,new Class[] { ConfigurableApplicationContext.class }, context);
			//准备上下文环境；将environment保存到ioc中；并且applyInitializers()
			//applyInitializers()：回调之前保存的所有ApplicationContextInitializer的initialize()方法
			//回调所有的SpringApplicationRunListeners的contextPrepared()方法
			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
			//prepareContext方法运行完成后，回调所有SpringApplicationRunListeners的contextLoaded()方法

			//刷新容器；ioc容器初始化(如果是web应用还会创建嵌入式的Tomcat)
			//扫描、创建、加载所有组件的地方；(配置类，组件，自动配置)
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
			}
			//回调所有的SpringApplicationRunListeners的started()方法
			listeners.started(context);
			//从ioc容器中获取所有的ApplicationRunner和CommandLineRunner
			//ApplicationRunner先回调，CommandLineRunner再回调
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}
		try {
			//回调所有的SpringApplicationRunListeners的running()方法
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		//整个SpringBoot应用启动完成以后返回启动的ioc容器
		return context;
	}