springboot-007启动配置的原理是什么

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));
    //判断当前项目是否是一个web应用
    this.webApplicationType = WebApplicationType.deduceFromClasspath();
    //从类路径下找到META-INF/spring.factories里配置的所有ApplicationContextInitializer，然后保存起来
    setInitializers((Collection) getSpringFactoriesInstances(
        ApplicationContextInitializer.class));
    //从类路径下找到META-INF/spring.factories里配置的所有ApplicationListener，然后保存起来
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    //从多个主配置类中找到包含main方法的主配置类
    this.mainApplicationClass = deduceMainApplicationClass();
}

/**
 * Run the Spring application, creating and refreshing a new
 * {@link ApplicationContext}.
 * @param args the application arguments (usually passed from a Java main method)
 * @return a running {@link ApplicationContext}
 */
public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    configureHeadlessProperty();
    
    //从类路径下找到META-INF/spring.factories里配置的所有SpringApplicationRunListener
    SpringApplicationRunListeners listeners = getRunListeners(args);
    
    //回调所有的SpringApplicationRunListener.starting()方法
    listeners.starting();
    try {
        //封装命令行参数
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(
            args);
        
        //准备环境
        //    1. 创建环境完成之后回调所有的SpringApplicationRunListener.environmentPrepared()方法，表示环境已经准备好了
        ConfigurableEnvironment environment = prepareEnvironment(listeners,
                                                                 applicationArguments);
        configureIgnoreBeanInfo(environment);
        Banner printedBanner = printBanner(environment);
        
        //创建ApplicationContext：决定是创建web应用的ioc，还是普通的ioc
        context = createApplicationContext();
        exceptionReporters = getSpringFactoriesInstances(
            SpringBootExceptionReporter.class,
            new Class[] { ConfigurableApplicationContext.class }, context);
        
        //准备上下文
        //    1. 将environment保存到ioc中；
        //    2. applyInitializers()：回调之前保存的所有ApplicationContextInitializer的initialize()方法
        //    3. listeners.contextPrepared()：回调之前保存的所有SpringApplicationRunListener的contextPrepared()方法
        //    4. listeners.contextLoaded()：contextPrepared运行完成之后，回调所有SpringApplicationRunListener的contextLoaded()方法
        prepareContext(context, environment, listeners, applicationArguments,
                       printedBanner);
        
        //刷新容器，即ioc容器的初始化（如果是web应用，还会初始化嵌入式的tomcat）
        //扫描、创建、加载所有组件的地方
        refreshContext(context);
        
        afterRefresh(context, applicationArguments);
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass)
                .logStarted(getApplicationLog(), stopWatch);
        }
        
        //回调所有的SpringApplicationRunListener.started()方法
        listeners.started(context);
        
        //从ioc容器中获取所有的ApplicationRunner和CommandLineRunner，然后进行回调
        //所有的ApplicationRunner优先于所有的CommandLineRunner进行回调
        callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, listeners);
        throw new IllegalStateException(ex);
    }

    try {
        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ioc容器
    return context;
}

#SpringApplicationRunListener
org.springframework.boot.SpringApplicationRunListener=\
com.qiang.springboot.listener.HelloSpringApplicationRunListener

##ApplicationContextInitializer
org.springframework.context.ApplicationContextInitializer=\
com.qiang.springboot.listener.HelloApplicationContextInitializer

public class HelloApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
    @Override
    public void initialize(ConfigurableApplicationContext configurableApplicationContext) {
        System.out.println("ApplicationContextInitializer...initialize..." + configurableApplicationContext);
    }
}

public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {
    public HelloSpringApplicationRunListener(SpringApplication application, String[] args) {
    }
    @Override
    public void starting() {
        System.out.println("SpringApplicationRunListener...starting...");
    }
    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        Object osName = environment.getSystemProperties().get("os.name");
        System.out.println("SpringApplicationRunListener...environmentPrepared..." + osName);
    }
    @Override
    public void contextPrepared(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...contextPrepared...");
    }
    @Override
    public void contextLoaded(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...contextLoaded...");
    }
    @Override
    public void started(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...started...");
    }
    @Override
    public void running(ConfigurableApplicationContext context) {
        System.out.println("SpringApplicationRunListener...running...");
    }
    @Override
    public void failed(ConfigurableApplicationContext context, Throwable exception) {
        System.out.println("SpringApplicationRunListener...failed...");
    }
}

@Component
public class HelloApplicationRunner implements ApplicationRunner {
    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println("ApplicationRunner...run..." + args);
    }
}

@Component
public class HelloCommandLineRunner implements CommandLineRunner {
    @Override
    public void run(String... args) throws Exception {
        System.out.println("CommandLineRunner...run..." + Arrays.asList(args));
    }
}