springboot启动配置原理

几个重要的事件回调机制
配置在META-INF/spring.factories
ApplicationContextInitializer
SpringApplicationRunListener
只需要放在ioc容器中
ApplicationRunner
CommandLineRunner
启动流程：

1、创建SpringApplication对象

initialize(sources);

private void initialize(Object[] sources) {
  //保存主配置类
  if (sources != null && sources.length > 0) {
    this.sources.addAll(Arrays.asList(sources));
  }
  //判断当前是否一个web应用
  this.webEnvironment = deduceWebEnvironment();
  //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ETA‐INF/spring.factories配置的所有ApplicationListener
  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();
}

listener

2、运行run

public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    FailureAnalyzers analyzers = null;
    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);
      //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ApplicationContext；决定创建web的ioc还是普通的ioc
      context = createApplicationContext();
      analyzers = new FailureAnalyzers(context);
      //准备上下文环境;将environment保存到ioc中；而且applyInitializers()；
      //applyInitializers()：回调之前保存的所有的ApplicationContextInitializer的initialize方法
      //回调所有的SpringApplicationRunListener的contextPrepared()；
      //
      prepareContext(context, environment, listeners, applicationArguments,
      printedBanner);
      //prepareContext运行完成以后回调所有的SpringApplicationRunListener的contextLoaded（）；
      //s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）；Spring注解版
      //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CommandLineRunner进行回调
      //ApplicationRunner先回调，CommandLineRunner再回调
      afterRefresh(context, applicationArguments);
      //所有的SpringApplicationRunListener回调finished方法
      listeners.finished(context, null);
      stopWatch.stop();
      if (this.logStartupInfo) {
        new StartupInfoLogger(this.mainApplicationClass)
        .logStarted(getApplicationLog(), stopWatch);
      }
      //整个SpringBoot应用启动完成以后返回启动的ioc容器；
      return context;
      }catch (Throwable ex) {
        handleRunFailure(context, listeners, analyzers, ex);
        throw new IllegalStateException(ex);
      }
}

3、事件监听机制

配置在META-INF/spring.factories
ApplicationContextInitializer

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

SpringApplicationRunListener

public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {
//必须有的构造器
  public HelloSpringApplicationRunListener(SpringApplication application, String[] args){
  }
  @Override
  public void starting() {
    System.out.println("SpringApplicationRunListener...starting...");
  }
  @Override
  public void environmentPrepared(ConfigurableEnvironment environment) {
    Object o = environment.getSystemProperties().get("os.name");
    System.out.println("SpringApplicationRunListener...environmentPrepared.."+o);
  }
  @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 finished(ConfigurableApplicationContext context, Throwable exception) {
    System.out.println("SpringApplicationRunListener...finished...");
  }
}

配置（META-INF/spring.factories）

org.springframework.context.ApplicationContextInitializer=\
com.atguigu.springboot.listener.HelloApplicationContextInitializer
org.springframework.boot.SpringApplicationRunListener=\
com.atguigu.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("ApplicationRunner...run....");
  }
}

CommandLineRunner

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