1、创建SpringApplication对象

2、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);
    // 回调所有的获取SpringApplicationRunListener.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);
        configureIgnoreBeanInfo(environment);
        // 创建环境完成后回调SpringApplicationRunListener.environmentPrepared();表示环境准备完成
        Banner printedBanner = printBanner(environment);
        // 创建ApplicationConetxt;决定创建web的ioc还是普通的ioc
        context = createApplicationContext();
        // 加载环境
        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的ApplicaionContextInitalizer的initialize方法
        // 回调所有的SpringApplicationRunLIstener的ContextPrepared();
        prepareContext(context, environment, listeners, applicationArguments, printedBanner);
        // preparedContext运行完成以后回调所有的SpringApplicationRunListener的contextLoaded();
        // 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);
        // 从ioc容器中获取所有的ApplicationRunner和CommadLineRunner进行回调
        // ApplicationRunner先回调，CommandLineRunner再回调
        afterRefresh(context, applicationArguments);
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
        }
        listeners.started(context);
        callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, listeners);
        throw new IllegalStateException(ex);
    }
    try {
        // 启动监听器
        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;
}

3、事件监听机制

配置在META-INF/spring.factories

ApplicationContextInitializer

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

SpringApplicationRunListener

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

配置（META-INF/spring.factories）

org.springframework.context.ApplicationContextInitializer=\
  com.zh.springboot.listener.HelloApplicationContextInitializer

org.springframework.boot.SpringApplicationRunListener=\
  com.zh.springboot.listener.HelloSpringApplicationRunListener

只需要放在IOC容器中

ApplicationRunner

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

CommandLineRunner

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

Java

Spring Boot-启动配置原理

1、创建SpringApplication对象

2、运行run方法

3、事件监听机制