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

• 第一步 加载main方法

    public static void main(String[] args) {
        ConfigurableApplicationContext applicationContext = SpringApplication.run(SpringbootdemoApplication.class, args);
    }
  ||
  \/
    public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
        return run(new Class<?>[] { primarySource }, args);
    }
  ||
  \/创建SpringApplication对象  -- >  运行run方法
    public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
        return new SpringApplication(primarySources).run(args);
    }
  ||
  \/  构造方法
    public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        this.webApplicationType = WebApplicationType.deduceFromClasspath();//判断一下环境类型
  //SpringFactoriesLoader -- > String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories";
    //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));
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = deduceMainApplicationClass();
    }

  7个初始化器
  
  11个***
  

• run方法的运行

  ||
  \/
    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ApplicationContext；决定创建web的ioc还是普通的ioc
            context = createApplicationContext();
            exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, 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);
            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 {
            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;
    }

使用自定义的初始化器

• 代码

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

• 配置（META-INF/spring.factories）

  org.springframework.context.ApplicationContextInitializer=\
  com.project.springbootdemo.component.HelloApplicationContextInitializer

  

自定义starter