Spring Boot启动配置原理

1、启动配置原理

1.1 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

在主程序类中打上断点，Debug，进行研究。

1.2 启动流程：

• 创建SpringApplication对象

// SpringApplication.class
public static ConfigurableApplicationContext run(Object source, String... args) {
  return run(new Object[]{source}, args);
}

public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
  return (new SpringApplication(sources)).run(args);
}

• 调用initialize(sources);方法

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, 即是否导入web模块
  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, 不着急用
  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();
}

找到ApplicationContextInitializer：

找到的Listener：

• 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);
  }
}

2、事件监听机制

来实现一下1.1节中提到的4个组件；

2.1 实现自定义ApplicationContextInitializer

Ctrl+n搜索ApplicationContextInitializer，选择ApplicationContextInitializer，Ctrl+h查看SpringBoot已经实现的所有Initializer：

// HelloApplicationContextInitializer.java
public class HelloApplicationContextInitializer implements 
    ApplicationContextInitializer<ConfigurableApplicationContext> {

  // 来监听ioc容器的启动
  @Override
  public void initialize(ConfigurableApplicationContext applicationContext) {
    System.out.println("ApplicationContextInitializer...initialize..."+applicationContext);
  }
}

2. 2 实现自定义SpringApplicationRunListener

// HelloSpringApplicationRunListener.java
public class HelloSpringApplicationRunListener implements SpringApplicationRunListener {

  //必须有的构造器, 传过来Spring应用和命令行参数
  public HelloSpringApplicationRunListener(SpringApplication application, String[] args){

  }

  // 监听容器开始
  @Override
  public void starting() {
      System.out.println("SpringApplicationRunListener...starting...");
  }

  @Override
  public void environmentPrepared(ConfigurableEnvironment configurableEnvironment) {
      Object o = configurableEnvironment.getSystemProperties().get("os.name");
      System.out.println("SpringApplicationRunListener...environmentPrepared.."+o);
  }

  @Override
  public void contextPrepared(ConfigurableApplicationContext configurableApplicationContext) {
      System.out.println("SpringApplicationRunListener...contextPrepared...");
  }

  // 容器环境加载完成
  @Override
  public void contextLoaded(ConfigurableApplicationContext configurableApplicationContext) {
      System.out.println("SpringApplicationRunListener...contextLoaded...");
  }

  @Override
  public void finished(ConfigurableApplicationContext configurableApplicationContext, 
      Throwable throwable) {

    System.out.println("SpringApplicationRunListener...finished...");
  }
}

以上两个组件想要起作用，必须配置（META-INF/spring.factories）；在我们引入的每个Jar包里，点开其目录结构中都有META-INF文件夹，里面有个spring.factories文件；

我们就要在resources文件夹下创建META-INF/spring.factories，并写入：

// copy Reference
org.springframework.context.ApplicationContextInitializer=\
com.initializr.initializer.HelloApplicationContextInitializer

org.springframework.boot.SpringApplicationRunListener=\
com.initializr.listener.HelloSpringApplicationRunListener

2.3 实现自定义ApplicationRunner

// 需要放在容器中的
@Component
public class HelloApplicationRunner implements ApplicationRunner {
  @Override
  public void run(ApplicationArguments applicationArguments) throws Exception {
    System.out.println("ApplicationRunner...run....");
  }
}

2.4 实现自定义CommandLineRunner

// 需要放在容器中的
@Component
public class HelloCommandLineRunner implements CommandLineRunner {
  @Override
  public void run(String... strings) throws Exception {
    System.out.println("CommandLineRunner...run..."+ Arrays.asList(strings));
  }
}

运行查看控制台有定义输出即可：