springboot启动过程

这个图做的很好：SpringBoot启动结构图

springboot启动分为构造器部分和run部分

构造器

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
    //初始化资源加载器
   this.resourceLoader = resourceLoader;
    //断言资源加载器不为null，否则报错
   Assert.notNull(primarySources, "PrimarySources must not be null");
    //初始化资源
   this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
    //推断当前的web应用类型（非WEB / SERVLET / REACTIVE）
   this.webApplicationType = WebApplicationType.deduceFromClasspath();
    //初始化bootstrap启动器，将所有pom中的start加载进来
   this.bootstrapRegistryInitializers = getBootstrapRegistryInitializersFromSpringFactories();
    //初始化spring.factories文件的所有组件信息，并放入缓存中
   setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
    //初始化应用监听器
   setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    //推断主程序类
   this.mainApplicationClass = deduceMainApplicationClass();
}

run方法

运行SpringApplication

创建上下文—启动监听器—创建IOC容器—准备环境—刷新IOC容器

public ConfigurableApplicationContext run(String... args) {
    //记录应用启动时间
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    //创建引导上下文，获得所有的bootstraps逐个执行
    DefaultBootstrapContext bootstrapContext = createBootstrapContext();
    ConfigurableApplicationContext context = null;
    //进入自力更生模式（Headless模式）
    configureHeadlessProperty();
    //获取到所有的listener
    SpringApplicationRunListeners listeners = getRunListeners(args);
    //遍历所有的listener调用starting方法，通知当前项目正在启动
    listeners.starting(bootstrapContext, this.mainApplicationClass);
    try {
        //保存命令行参数
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
        //准备环境
        ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
        //配置忽略信息
        configureIgnoreBeanInfo(environment);
        //打印bannner
        Banner printedBanner = printBanner(environment);
        //创建IOC容器
        context = createApplicationContext();
        //设置start
        context.setApplicationStartup(this.applicationStartup);
        //准备环境信息
        prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
        //刷新IOC容器，创建容器中的所有组件
        refreshContext(context);
        //刷新后需要完成的工作
        afterRefresh(context, applicationArguments);
        //记录停止时间
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
        }
        //向观察者发布上下文已启动
        listeners.started(context);
        //调用所有runners
        callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, listeners);
        throw new IllegalStateException(ex);
    }
    try {
        //向观察者发布上下文已就绪
        listeners.running(context);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, null);
        throw new IllegalStateException(ex);
    }
    //返回应用上下文
    return context;
}

几个比较重要的步骤

准备上下文环境

也是创建IOC容器—createApplicationContext

根据当前项目类型创建容器，最后返回一个AnnotationConfigServletWebServerApplicationContext容器对象

保存当前环境信息

应用初始化器applyInitializers，遍历并调用对IOC容器进行初始化

通知所有的监听器

刷新IOC容器refreshContext(context)

这个涉及的内容比较多，打算单独在开一篇文章，作用就是实例化了bean

@Override
public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
      //设置容器状态，初始化
      prepareRefresh();
      //获取bean工厂
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
	  //准备bean工厂
      prepareBeanFactory(beanFactory);
      try {
         //bean工厂后置处理器
         postProcessBeanFactory(beanFactory);
         StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
         //实现bean工厂的后置处理器
         invokeBeanFactoryPostProcessors(beanFactory);
         // 注册bean工厂的后置处理器
         registerBeanPostProcessors(beanFactory);
         beanPostProcess.end();
         //初始化消息源
         initMessageSource();
         //初始化时间广播器
         initApplicationEventMulticaster();
         //初始化特定子类及特殊bean
         onRefresh();
         //检查监听器并注册
         registerListeners();
         //实例化所有的单例（非lazy）
         finishBeanFactoryInitialization(beanFactory);
         //刷新，发布相应的事件
         finishRefresh();
      }
		//catch、finally省略
   }
}