SpringBoot之启动配置原理

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

---

一、启动流程：

以main方法为入口：

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();
}

2、运行run方法

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（）；

      //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

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

---

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));
    }
}

只需要放在ioc容器中

---

二、自动配置

• Spring Boot启动时扫描所有jar包的META-INF/spring.factories中配置的
EnableAutoConfiguration组件

• spring-boot-autoconfigure.jar/META-INF/spring.factories配置了启动时需要加载的
EnableAutoConfiguration组件

• 配置文件中使用debug=true可以观看到当前启用的自动配置的信息

• 自动配置会为容器中添加大量组件

• Spring Boot在做任何功能都需要从容器中获取这个功能的组件

• Spring Boot总是遵循一个标准：容器中有我们自己配置的组件就用我们配置的，没有就用自动配
置默认注册进来的组件