SpringBoot启动流程原理解析（二）

在上一章我们分析了SpingBoot启动流程中实例化SpingApplication的过程。

return new SpringApplication(primarySources).run(args);
这篇文章咱么说下run()方法开始之后都做了那些事情。

继续往下跟着源码进入到run()这个是比较核心的一个方法了

    public ConfigurableApplicationContext run(String... args) {
        StopWatch stopWatch = new StopWatch();
                // 计时器开始
        stopWatch.start();
                // 创建启动上下文对象
        DefaultBootstrapContext bootstrapContext = createBootstrapContext();
        ConfigurableApplicationContext context = null;
                // 配置Handless模式，是在缺少显示屏、键盘或鼠标时的系统配置
                // 默认为true
        configureHeadlessProperty();
                //获取并启动监听器
        SpringApplicationRunListeners listeners = getRunListeners(args);
                // 启动监听器
        listeners.starting(bootstrapContext, this.mainApplicationClass);
        try {
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
                        // 准备环境
            ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
                        // 忽略配置的bean
            configureIgnoreBeanInfo(environment);
                        // 打印banner,就是启动的时候在控制台的spring图案
            Banner printedBanner = printBanner(environment);
                        // 创建容器
            context = createApplicationContext();
            context.setApplicationStartup(this.applicationStartup);
                        // 准备应用上下文(spring容器前置处理)
            prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
                        // 刷新容器
            refreshContext(context);
                        // 刷新容器后的扩展接口(spring容器后置处理)
            afterRefresh(context, applicationArguments);
                        // 结束计时器并打印，这就是我们启动后console的显示的时间
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
            }
                        // 发布监听应用上下文启动完成（发出启动结束事件）
            listeners.started(context);
                        // 执行runner
            callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
                        // 异常处理，如果run过程发生异常
            handleRunFailure(context, ex, listeners);
            throw new IllegalStateException(ex);
        }

        try {
                        // 监听应用上下文运行中
            listeners.running(context);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, null);
            throw new IllegalStateException(ex);
        }
                // 返回最终构建的容器对象
        return context;
    }

接下来就对上面的关键步骤一一解释

1. 获取所有的监听器

这段代码我们比较熟悉了，上一篇咱么详细介绍过，它的主要作用就是去META-INFO/spring.factories 中加载配置SpringApplicationRunListener的监听器如下

显然只有一个事件发布监听器类，拿到了EventPublishingRunListener启动事件发布监听器，下一步就是开始启动了listeners.starting（）;我们往下跟源码看

    @Override
    public void starting(ConfigurableBootstrapContext bootstrapContext) {
        this.initialMulticaster
                .multicastEvent(new ApplicationStartingEvent(bootstrapContext, this.application, this.args));
    }

启动的时候实际上是又创建了一个ApplicationStartingEvent对象，其实就是监听应用启动事件。
其中 initialMulticaster是一个SimpleApplicationEventMuticaster

    public void multicastEvent(ApplicationEvent event, @Nullable ResolvableType eventType) {
        ResolvableType type = eventType != null ? eventType : this.resolveDefaultEventType(event);
        // 获取线程池，为每个监听事件创建一个线程
        Executor executor = this.getTaskExecutor();
        // 根据ApplicationStartingEvent事件类型找到对应的监听器，并迭代 
        Iterator var5 = this.getApplicationListeners(event, type).iterator();

        while(var5.hasNext()) {
            ApplicationListener<?> listener = (ApplicationListener)var5.next();
            if (executor != null) {
                // 
                executor.execute(() -> {
                    this.invokeListener(listener, event);
                });
            } else {
                this.invokeListener(listener, event);
            }
        }

    }

2.准备环境

ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);

    private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
            DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) {
        // Create and configure the environment
                // 这里我们加入了web依赖所以是一个servlet容器
        ConfigurableEnvironment environment = getOrCreateEnvironment();
                // 配置环境
        configureEnvironment(environment, applicationArguments.getSourceArgs());
                // 环境准备完成
        ConfigurationPropertySources.attach(environment);
        listeners.environmentPrepared(bootstrapContext, environment);
        DefaultPropertiesPropertySource.moveToEnd(environment);
        configureAdditionalProfiles(environment);
        bindToSpringApplication(environment);
        if (!this.isCustomEnvironment) {
            environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
                    deduceEnvironmentClass());
        }
        ConfigurationPropertySources.attach(environment);
        return environment;
    }

由于我们是添加了web的依赖 getOrCreateEnvironment（）返回的是一个standardservletEnviroment 标准的servlet环境

2.1 配置环境

    protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
        if (this.addConversionService) {
                        // 嵌入式的转换器
            ConversionService conversionService = ApplicationConversionService.getSharedInstance();
            environment.setConversionService((ConfigurableConversionService) conversionService);
        }
                // 配置属性资源文件
        configurePropertySources(environment, args);
                // 配置文件
        configureProfiles(environment, args);
    }

应用嵌入的转换器ApplicationConversionService

    public static void configure(FormatterRegistry registry) {
        DefaultConversionService.addDefaultConverters(registry);
        DefaultFormattingConversionService.addDefaultFormatters(registry);
                // 格式转换
        addApplicationFormatters(registry);
                // 类型转换
        addApplicationConverters(registry);
    }

        ===============格式转换=================
    public static void addApplicationFormatters(FormatterRegistry registry) {
        registry.addFormatter(new CharArrayFormatter());
        registry.addFormatter(new InetAddressFormatter());
        registry.addFormatter(new IsoOffsetFormatter());
    }


        ========================类型转换===================
    public static void addApplicationConverters(ConverterRegistry registry) {
        addDelimitedStringConverters(registry);
        registry.addConverter(new StringToDurationConverter());
        registry.addConverter(new DurationToStringConverter());
        registry.addConverter(new NumberToDurationConverter());
        registry.addConverter(new DurationToNumberConverter());
        registry.addConverter(new StringToPeriodConverter());
        registry.addConverter(new PeriodToStringConverter());
        registry.addConverter(new NumberToPeriodConverter());
        registry.addConverter(new StringToDataSizeConverter());
        registry.addConverter(new NumberToDataSizeConverter());
        registry.addConverter(new StringToFileConverter());
        registry.addConverter(new InputStreamSourceToByteArrayConverter());
        registry.addConverterFactory(new LenientStringToEnumConverterFactory());
        registry.addConverterFactory(new LenientBooleanToEnumConverterFactory());
        if (registry instanceof ConversionService) {
            addApplicationConverters(registry, (ConversionService) registry);
        }
    }
    

2.2 环境准备完成

同上面启动监听事件，这次的环境准备也是同样的代码

    @Override
    public void environmentPrepared(ConfigurableBootstrapContext bootstrapContext,
            ConfigurableEnvironment environment) {
        this.initialMulticaster.multicastEvent(
                                // 创建一个应用环境准备事件对象
                new ApplicationEnvironmentPreparedEvent(bootstrapContext, this.application, this.args, environment));
    }

debug进去之后代码跟AppLicationstrigevent 事件对象是一样的。不再赘述。
不过这里是7个监听器对象

3.配置忽略的bean

configureIgnoreBeanInfo(environment);

4.打印banner

这是SpringBoot默认的启动时的图标
Banner printedBanner = printBanner(environment);

这个是可以自定义的，也可以是图篇或是文本文件中的图形

5.创建容器

紧接着上一篇，接下来就是创建容器

    protected ConfigurableApplicationContext createApplicationContext() {
        return this.applicationContextFactory.create(this.webApplicationType);
    }

6.准备应用上下文

    private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,
            ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
            ApplicationArguments applicationArguments, Banner printedBanner) {
                // 设置环境参数
        context.setEnvironment(environment);
                // 设置后处理应用上下文
        postProcessApplicationContext(context);
                //把从spring.factories中加载的org.springframework.bt.context.ConfigurationwarningsApplicationContextIitiaLizer，进行初始化操作
        applyInitializers(context);
                //EventPubLishingRunListener发布应用上下文事件 
        listeners.contextPrepared(context);
                // 打印启动日志
        bootstrapContext.close(context);
        if (this.logStartupInfo) {
            logStartupInfo(context.getParent() == null);
            logStartupProfileInfo(context);
        }
        // Add boot specific singleton beans
                
        ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
        if (printedBanner != null) {
                         //注册一个字是springAppLicationArguments单例的bean 
            beanFactory.registerSingleton("springBootBanner", printedBanner);
        }
        if (beanFactory instanceof DefaultListableBeanFactory) {
            ((DefaultListableBeanFactory) beanFactory)
                    .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
        }
        if (this.lazyInitialization) {
            context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
        }
        // Load the sources 获取所有资源
        Set<Object> sources = getAllSources();
        Assert.notEmpty(sources, "Sources must not be empty");
                // 创建BeanDefinitionLoader加载器加载注册所有的资源 
        load(context, sources.toArray(new Object[0]));
                // 同之前，发布应用上下文 加载事件 
        listeners.contextLoaded(context);
    }

7.刷新应用上下文

刷新应用上下文就进入了spring的源码了

    public void refresh() throws BeansException, IllegalStateException {
        synchronized(this.startupShutdownMonitor) {
            StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
            // Prepare this context for refreshing.
            //准备刷新上下文
            this.prepareRefresh();
            // Tetl the subclass to refresh the internal bean facto
            // 通知子类刷新内部工厂
            ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
            // Prepare the bean factory for use in this context.
            // 准备Bean工厂
            this.prepareBeanFactory(beanFactory);

            try {
                 // Allows post-processing of the bean factory in contex t subc lasses.
                // 允许在上下文子类中对bean工厂进行后处理。
                // Invoke factory processors registered as beans in the context,
                this.postProcessBeanFactory(beanFactory);
                StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
                this.invokeBeanFactoryPostProcessors(beanFactory);
                // 注册后置处理器。
                this.registerBeanPostProcessors(beanFactory);
                beanPostProcess.end();
                // 初始化信息源
                this.initMessageSource();
                // 初始化上下文事件发布器
                this.initApplicationEventMulticaster();
                // 初始化其他自定义bean 
                this.onRefresh();
                // 注册监听器
                this.registerListeners();
                this.finishBeanFactoryInitialization(beanFactory);
                //完成刷新，清缓存，初始化生命周期，事件发布等
                this.finishRefresh();
            } catch (BeansException var10) {
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var10);
                }
                // 销毁bean 
                this.destroyBeans();
                // Reset 'active'flag.
                this.cancelRefresh(var10);
                throw var10;
            } finally {
                this.resetCommonCaches();
                contextRefresh.end();
            }

        }
    }

刷新的代码有点深，也是在这时创建了Tomcat对象，这也是SpringBoot 一键启动web工程的关键

创建了Tomcat对象，并设置参数

    @Override
    public WebServer getWebServer(ServletContextInitializer... initializers) {
        if (this.disableMBeanRegistry) {
            Registry.disableRegistry();
        }
        Tomcat tomcat = new Tomcat();
        File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
        tomcat.setBaseDir(baseDir.getAbsolutePath());
        Connector connector = new Connector(this.protocol);
        connector.setThrowOnFailure(true);
        tomcat.getService().addConnector(connector);
        customizeConnector(connector);
        tomcat.setConnector(connector);
        tomcat.getHost().setAutoDeploy(false);
        configureEngine(tomcat.getEngine());
        for (Connector additionalConnector : this.additionalTomcatConnectors) {
            tomcat.getService().addConnector(additionalConnector);
        }
        prepareContext(tomcat.getHost(), initializers); 
                // 返回TomcatWebServer服务
        return getTomcatWebServer(tomcat);
    }

8.刷新后处理

afterReftesh(); //是个一空实现，留着后期扩展

    /**
     * Called after the context has been refreshed.
     * @param context the application context
     * @param args the application arguments
     */
    protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args) {
    }

9.发布监听应用启动事件

    @Override
    public void started(ConfigurableApplicationContext context) {
        context.publishEvent(new ApplicationStartedEvent(this.application, this.args, context));
        AvailabilityChangeEvent.publish(context, LivenessState.CORRECT);
    }

这里是调用context.publishEvent（）方法，发布应用启动事件ApplicationStartedEvent.

10.执行Runner

获取所有的ApplicationRuner和CommandLineRunner来初始化一些参数，callRuner（是一个回调函数)

    private void callRunners(ApplicationContext context, ApplicationArguments args) {
        List<Object> runners = new ArrayList<>();
        runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
        runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
        AnnotationAwareOrderComparator.sort(runners);
        for (Object runner : new LinkedHashSet<>(runners)) {
            if (runner instanceof ApplicationRunner) {
                callRunner((ApplicationRunner) runner, args);
            }
            if (runner instanceof CommandLineRunner) {
                callRunner((CommandLineRunner) runner, args);
            }
        }
    }

11.发布上下文准备完成的事件

listeners.running(context);

    @Override
    public void running(ConfigurableApplicationContext context) {
        context.publishEvent(new ApplicationReadyEvent(this.application, this.args, context));
        AvailabilityChangeEvent.publish(context, ReadinessState.ACCEPTING_TRAFFIC);
    }

这段代码看上去似成相识，前面有很多类似的代码，不同的是这里上下文准备完成之后发布了一个ApplicationReadyEvent事件，声明一下应用上下文准备完成。

小结

这篇主要是介绍了SpringBoot启动过程中run（）的这个过程。从中我们也可以发现一些非常好的编码习惯，大家可以在日常的工作中从模仿到内化，慢慢变成自己的东西。

如果你最近正在学习SpringBoot，可以参考我的个人网站：程序员波特，目前已经更新了SpringBoot2.x，SpringBoot3.x的系列学习教程，希望可以帮助到你。