Springboot的启动过程总结

​​ Springboot的启动过程总结 ​ ​

1、总体步骤分两个

• 创建Spring 应用（创建SpringApplication）

• 运行Spring 应用（运行SpringApplication）

2、创建Spring 应用（创建SpringApplication）

就是new 一个对象，构造器里面做一些初始化的动作

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
    this.resourceLoader = resourceLoader;
    Assert.notNull(primarySources, "PrimarySources must not be null");
    this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
    //判断应用的类型deduce v.  推论; 推断; 演绎;的意思
    this.webApplicationType = WebApplicationType.deduceFromClasspath();
    //设置初始化器，保存起来 从spring.factories 找
    setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
    //设置监听器、保存起来从spring.factories 找
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    //主应用类是那个
    this.mainApplicationClass = deduceMainApplicationClass();
  }

3、运行Spring 应用（运行SpringApplication）

public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    configureHeadlessProperty();
               //获取所有的运行监听器:就一个EventPublishingRunListener从spring.factories 中找的
    SpringApplicationRunListeners listeners = getRunListeners(args);
    listeners.starting();
    try {
      ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
      //准备环境，如果有的话就不创建了，没有就创建一个
                        ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
      configureIgnoreBeanInfo(environment);
      Banner printedBanner = printBanner(environment);
      context = createApplicationContext();
      exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
          new Class[] { ConfigurableApplicationContext.class }, context);
      prepareContext(context, environment, listeners, applicationArguments, printedBanner);
      refreshContext(context);
      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);
    }
    return context;
}

3.1 prepareEnvironment 方法说明

/**

*

*  获取或者创建一个Environment对象，如果我们自己在main 方法里面创建了一个Environment，并放到

*        SpringApplication 中了就不创建了，

*        SpringApplication application = new SpringApplication(ProfileDemoApplication.class);

*        ConfigurableEnvironment environment = new StandardEnvironment();

*        environment.setActiveProfiles("dev");

*        application.setEnvironment(environment);

*  否则就创建

*

*

*/

注意：以下的说明

// 添加初始的properties（注意：当前并未加载如application.properties/yml的properties）

// 添加初始的profile（注意：当前并未加载如application.properties/yml配置profile）

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
      ApplicationArguments applicationArguments) {
    //创建或者获取一个Environment 对象
    ConfigurableEnvironment environment = getOrCreateEnvironment();

//配置environment
    configureEnvironment(environment, applicationArguments.getSourceArgs());
    ConfigurationPropertySources.attach(environment);

// 触发监听器（主要是触发ConfigFileApplicationListener，这个监听器将会加载如application.properties/yml这样的配置文件）

//通知所有的监听器 环境准备好了
    listeners.environmentPrepared(environment);
    bindToSpringApplication(environment);
    if (!this.isCustomEnvironment) {
      environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
          deduceEnvironmentClass());
    }

ConfigurationPropertySources.attach(environment);
    return environment;
  }