Spring Boot啓動配置原理

幾個重要的事件回調機制

配置在META-INF/spring.factories

ApplicationContextInitializer

SpringApplicationRunListener

只須要放在ioc容器中

ApplicationRunner

CommandLineRunner

啓動流程：

一、建立SpringApplication對象

initialize(sources);
private void initialize(Object[] sources) {
    //保存主配置類
    if (sources != null && sources.length > 0) {
        this.sources.addAll(Arrays.asList(sources));
    }
    //判斷當前是否一個web應用
    this.webEnvironment = deduceWebEnvironment();
    //從類路徑下找到META-INF/spring.factories配置的全部ApplicationContextInitializer；而後保存起來
    setInitializers((Collection) getSpringFactoriesInstances(
        ApplicationContextInitializer.class));
    //從類路徑下找到ETA-INF/spring.factories配置的全部ApplicationListener
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    //從多個配置類中找到有main方法的主配置類
    this.mainApplicationClass = deduceMainApplicationClass();
}

二、運行run方法

public ConfigurableApplicationContext run(String... args) {
   StopWatch stopWatch = new StopWatch();
   stopWatch.start();
   ConfigurableApplicationContext context = null;
   FailureAnalyzers analyzers = null;
   configureHeadlessProperty();

   //獲取SpringApplicationRunListeners；從類路徑下META-INF/spring.factories
   SpringApplicationRunListeners listeners = getRunListeners(args);
    //回調全部的獲取SpringApplicationRunListener.starting()方法
   listeners.starting();
   try {
       //封裝命令行參數
      ApplicationArguments applicationArguments = new DefaultApplicationArguments(
            args);
      //準備環境
      ConfigurableEnvironment environment = prepareEnvironment(listeners,
            applicationArguments);
               //建立環境完成後回調SpringApplicationRunListener.environmentPrepared()；表示環境準備完成

      Banner printedBanner = printBanner(environment);

       //建立ApplicationContext；決定建立web的ioc仍是普通的ioc
      context = createApplicationContext();

      analyzers = new FailureAnalyzers(context);
       //準備上下文環境;將environment保存到ioc中；並且applyInitializers()；
       //applyInitializers()：回調以前保存的全部的ApplicationContextInitializer的initialize方法
       //回調全部的SpringApplicationRunListener的contextPrepared()；
       //
      prepareContext(context, environment, listeners, applicationArguments,
            printedBanner);
       //prepareContext運行完成之後回調全部的SpringApplicationRunListener的contextLoaded（）；

       //s刷新容器；ioc容器初始化（若是是web應用還會建立嵌入式的Tomcat）；Spring註解版
       //掃描，建立，加載全部組件的地方；（配置類，組件，自動配置）
      refreshContext(context);
       //從ioc容器中獲取全部的ApplicationRunner和CommandLineRunner進行回調
       //ApplicationRunner先回調，CommandLineRunner再回調
      afterRefresh(context, applicationArguments);
       //全部的SpringApplicationRunListener回調finished方法
      listeners.finished(context, null);
      stopWatch.stop();
      if (this.logStartupInfo) {
         new StartupInfoLogger(this.mainApplicationClass)
               .logStarted(getApplicationLog(), stopWatch);
      }
       //整個SpringBoot應用啓動完成之後返回啓動的ioc容器；
      return context;
   }
   catch (Throwable ex) {
      handleRunFailure(context, listeners, analyzers, ex);
      throw new IllegalStateException(ex);
   }
}

三、事件監聽機制

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 {

    //必須有的構造器
    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

只須要放在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));
    }
}