SpringBoot分析之启动原理-AbstractApplic

Spring初始化Ioc容器很重要的一个方法是由ApplicationContext子接口ConfigurableApplicationContext提供的refresh(),这个方法的作用是创建加载Spring容器配置（包括.xml配置，property文件和数据库模式等）

本文主要是整体启动流程请查看springboot原理(核心原理、启动流程、执行流程)中的11. 调用ApplicationContext的refresh()方法,装配context beanfactory等非常重要的核心组件的源码分析：SpringBoot分析之启动原理-AbstractApplicationContext#refresh()

本系列源码都是基于spring-4.3.8版本之上，其他版本略有差异，但总体的核心思想相同。同时，为了使贴出的源代码尽可能的紧凑，可能会删去一些异常捕获、日志输出等代码。若文中存在纰漏错误，欢迎指正。

    public void refresh() throws BeansException, IllegalStateException {
        // 准备刷新上下文
        prepareRefresh();
 
        /**
         * 构建beanFactory，其实是构建DefaultListableBeanFactory，
         * 这是一个非常重要的方法，spring对xml的解析就在这里进行，并将xml中的各种tag解析成具体的BeanDefinition，
         * 并注册到beanFactory。
         */
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
 
        /**
         * 准备初始化beanFactory，内部将一些系统bean注册到beanFactory， 
         * 如用于读取配置文件的StandardEnvironment
         */
        prepareBeanFactory(beanFactory);
 
        // 用于添加一些BeanPostProcessor，并注册一些内置的objectFactory
        postProcessBeanFactory(beanFactory);
 
        // 排序并执行所有的BeanFactoryPostProcessor、BeanDefinitionRegistryPostProcessor
        invokeBeanFactoryPostProcessors(beanFactory);
 
        // 排序并注册BeanPostProcessor，BeanPostProcessor作用是用于拦截Bean的创建
        registerBeanPostProcessors(beanFactory);
 
        // 初始化MessageSource
        initMessageSource();
 
        // 初始化ApplicationEventMulticaster
        initApplicationEventMulticaster();
 
        // 初始化其他的特殊bean
        onRefresh();
 
        // 检查、注册监听器
        registerListeners();
 
        // 实例化所有非延迟加载的单例Bean
        finishBeanFactoryInitialization(beanFactory);
 
        // 主要是一些生命周期相关组件的功能
        finishRefresh();
    }

• prepareRefresh

    protected void prepareRefresh() {
        this.startupDate = System.currentTimeMillis();
        this.closed.set(false);
        this.active.set(true);
 
        if (logger.isInfoEnabled()) {
            logger.info("Refreshing " + this);
        }
 
        // Initialize any placeholder property sources in the context environment
        initPropertySources();
 
        // Validate that all properties marked as required are resolvable
        // see ConfigurablePropertyResolver#setRequiredProperties
        getEnvironment().validateRequiredProperties();
 
        // Allow for the collection of early ApplicationEvents,
        // to be published once the multicaster is available...
        this.earlyApplicationEvents = new LinkedHashSet<ApplicationEvent>();
    }

• obtainFreshBeanFactory

    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        /**
         * 该方法主要做了两件事 
         * 1、创建核心的bean工厂-DefaultListableBeanFactory
         * 2、开始加载配置文件并注册bean，如：ioc容器的xml或@Configuration注解启动的类
         */
        refreshBeanFactory();
        // 其实只是简单的获取了上面创建的DefaultListableBeanFactory而已
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }

refreshBeanFactory方法在AbstractApplicationContext中只是一个抽象方法，这里就以使用相对频繁的子类AbstractRefreshableApplicationContext为例。

    protected final void refreshBeanFactory() throws BeansException {
        // 若已存在bean工厂，则先销毁
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {
            // 创建bean工厂，即DefaultListableBeanFactory，若存在父级beanFactory也会设置到自身的parentBeanFactory中
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            beanFactory.setSerializationId(getId());
            /**
             * 设置两个变量到当前beanFactory
             * allowBeanDefinitionOverriding-允许BeanDefinition被覆盖，若为false，则存在相同的beanName会直接抛出异常
             * allowCircularReferences-允许BeanDefinition被循环引用，若为false，则若发生两个组件相互依赖时，会抛出异常
             */
            customizeBeanFactory(beanFactory);
            /**
             * 这是一个抽象方法，用于加载BeanDefinition，根据不同的子ApplicationContext实现可以以不同形式注册组件 如：
             * xml启动以XmlWebApplicationContext进行逐个加载ioc的各个xml
             * 注解启动以AnnotationConfigWebApplicationContext进行逐个加载含有@Component注解的组件
             */
            loadBeanDefinitions(beanFactory);
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        } catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(),
                    ex);
        }
    }

• prepareBeanFactory

    protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // 给beanFactory设置类加载器
        beanFactory.setBeanClassLoader(getClassLoader());
        // 设置EL表达式解析器（很多地方会使用到，如springMvc解析请求入参、@Autowired、@Resource等注解的注入参数等）
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        // 添加属性
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
 
        /**
         * 设置ApplicationContextAwareProcessor，
         * 用于在bean实例化时，前置调用ApplicationContextAware、EnvironmentAware等Aware接口实现，以注入对应的值
         */
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        /**
         * <a href="https://www.jianshu.com/p/3c7e0608ff1f">具体作用可参考</a>
         * 将刚刚在前置处理中触发的六个Aware接口加入到ignoredDependencyInterfaces
         * 凡加入ignoredDependencyInterfaces的类，都不会进行依赖检查或自动装配
         */
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
 
        /**
         * 将以下四个接口（以key-依赖类型，value-实际值的方式）注册到resolvableDependencies，
         * 被加入resolvableDependencies的类可以@Autowired、@Resource、@Injected或@Value的方式注入的其他的bean，
         * 同时，若注入的类型为ObjectFactory的实现时，自动注入的注解将会注入ObjectFactory#getObject的对象
         */
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);
 
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
 
        // 若没有手动添加过【loadTimeWeaver】，则将默认注册单例LoadTimeWeaverAwareProcessor到单例beanFactory
        if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            // Set a temporary ClassLoader for type matching.
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
 
        /**
         * 若没有手动添加过【environment】，则将默认注册单例StandardEnvironment到单例beanFactory，
         * 可用于解析xml中的el表达式、注入@Value注解修饰的变量等
         */
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
        }
        // 若没有手动添加过【systemProperties】，则将默认注册单例System#getProperties（与jvm相关的变量）即系统环境到单例beanFactory
        if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
        }
        // 若没有手动添加过【systemEnvironment】，则将默认注册单例System#getenv（即系统环境变量）到单例beanFactory
        if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
        }
    }

• postProcessBeanFactory

    protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        /**
         * 添加ServletContextAwareProcessor，用于给自定义组件注入ServletContext、ServletConfig
         * 需要注意的是内部的beanPostProcessors是一个ArrayList，所以其内部是有序的， 按照添加顺序进行逐个执行
         */
        beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
        beanFactory.ignoreDependencyInterface(ServletContextAware.class);
        beanFactory.ignoreDependencyInterface(ServletConfigAware.class);
 
        /**
         * 注册web组件，如ServletRequest、ServletResponse、HttpSession等，
         * 统一添加到DefaultListableBeanFactory#resolvableDependencies，
         */
        WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
        // 注册一些环境相关的单例bean到DefaultListableBeanFactory
        WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
    }

    public static void registerWebApplicationScopes(ConfigurableListableBeanFactory beanFactory, ServletContext sc) {
        // 分别注册三个域，用于获取每个域对应的bean时使用
        beanFactory.registerScope(WebApplicationContext.SCOPE_REQUEST, new RequestScope());
        beanFactory.registerScope(WebApplicationContext.SCOPE_SESSION, new SessionScope(false));
        beanFactory.registerScope(WebApplicationContext.SCOPE_GLOBAL_SESSION, new SessionScope(true));
        if (sc != null) {
            ServletContextScope appScope = new ServletContextScope(sc);
            beanFactory.registerScope(WebApplicationContext.SCOPE_APPLICATION, appScope);
            // Register as ServletContext attribute, for ContextCleanupListener to detect it.
            sc.setAttribute(ServletContextScope.class.getName(), appScope);
        }
 
        /**
         * 注册ServletRequest、ServletResponse等以及对应的objectFactory到DefaultListableBeanFactory
         * 如SpringMvc的Controller在实例变量中注入Request、Response就是依靠这里的objectFactory获取线程变量实现的
         */
        beanFactory.registerResolvableDependency(ServletRequest.class, new RequestObjectFactory());
        beanFactory.registerResolvableDependency(ServletResponse.class, new ResponseObjectFactory());
        beanFactory.registerResolvableDependency(HttpSession.class, new SessionObjectFactory());
        beanFactory.registerResolvableDependency(WebRequest.class, new WebRequestObjectFactory());
        if (jsfPresent) {
            FacesDependencyRegistrar.registerFacesDependencies(beanFactory);
        }
    }

• invokeBeanFactoryPostProcessors

    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        // 执行所有的BeanFactoryPostProcessor、BeanDefinitionRegistryPostProcessor
        PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
 
        // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
        // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
        if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
    }

    public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory,
            List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
 
        /**
         * 整个方法比较长，整体思路如下：
         * 1、先分类并排序后执行BeanDefinitionRegistryPostProcessor
         * 2、然后执行BeanFactoryPostProcessor
         */
        Set<String> processedBeans = new HashSet<String>();
 
        /**
         * 一般而言，beanFactory都是能转化成BeanDefinitionRegistry
         * DefaultListableBeanFactory就实现了BeanDefinitionRegistry
         */
        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
            List<BeanDefinitionRegistryPostProcessor> registryPostProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();
 
            /**
             * 开始对所有beanFactoryPostProcessors进行分类
             * 若能转换为BeanDefinitionRegistryPostProcessor则加入registryPostProcessors，
             * 否则加入regularPostProcessors。
             */
            for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryPostProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor;
                    registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryPostProcessors.add(registryPostProcessor);
                } else {
                    regularPostProcessors.add(postProcessor);
                }
            }
 
            /**
             * 从beanFactory中获取所有实现了BeanDefinitionRegistryPostProcessor的bean
             */
            String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class,
                    true, false);
 
            /**
             * 1、开始分类整理这些BeanDefinitionRegistryPostProcessor，
             * 优先获取实现了PriorityOrdered的bean，并排序后逐个执行
             */
            List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
            for (String ppName : postProcessorNames) {
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    priorityOrderedPostProcessors
                            .add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
            registryPostProcessors.addAll(priorityOrderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);
 
            /**
             * 2、重新分类整理这些BeanDefinitionRegistryPostProcessor， 这次获取实现了Ordered的bean，并排序后逐个执行
             */
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true,
                    false);
            List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
            for (String ppName : postProcessorNames) {
                if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(beanFactory, orderedPostProcessors);
            registryPostProcessors.addAll(orderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);
 
            /**
             * 3、再一次获取这些这些BeanDefinitionRegistryPostProcessor，并逐个执行
             */
            boolean reiterate = true;
            while (reiterate) {
                reiterate = false;
                postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true,
                        false);
                for (String ppName : postProcessorNames) {
                    if (!processedBeans.contains(ppName)) {
                        BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName,
                                BeanDefinitionRegistryPostProcessor.class);
                        registryPostProcessors.add(pp);
                        processedBeans.add(ppName);
                        pp.postProcessBeanDefinitionRegistry(registry);
                        reiterate = true;
                    }
                }
            }
 
            // 开始分类执行BeanFactoryPostProcessor
            invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
        }
 
        else {
            // 对没有实现BeanDefinitionRegistry的beanFactory，直接不分类，粗暴执行这些BeanFactoryPostProcessor
            invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
        }
 
        // 从beanFactory中获取所有实现了BeanFactoryPostProcessor的bean
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
 
        // 开始分类，分类原则与BeanDefinitionRegistryPostProcessor相同
        List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (processedBeans.contains(ppName)) {
                // skip - already processed in first phase above
            } else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
            } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            } else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }
 
        // 首先，执行实现了PriorityOrdered的BeanFactoryPostProcessor
        sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
 
        // 然后，执行实现了Ordered的BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : orderedPostProcessorNames) {
            orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        sortPostProcessors(beanFactory, orderedPostProcessors);
        invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
 
        // 最后，执行剩余的BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : nonOrderedPostProcessorNames) {
            nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
 
        beanFactory.clearMetadataCache();
    }

• registerBeanPostProcessors

    protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
    }

    public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory,
            AbstractApplicationContext applicationContext) {
 
        /**
         * 若理解了上一步的invokeBeanFactoryPostProcessors， 那这里就理解起来就相当容易了，
         * 唯一有区别的是由于这里是注册BeanPostProcessor，而BeanPostProcessor是在每个bean实例化前后调用的，
         * 所以这里只是单独的注册到beanFactory，并没有逐个执行
         */
        // 从beanFactory中获取所有BeanPostProcessor的beanName
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
 
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
 
        // 开始根据beanName遍历BeanPostProcessor，并按照PriorityOrdered、Ordered以及其他进行分类
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
 
        for (String ppName : postProcessorNames) {
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            } else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }
 
        // 1、排序并注册实现了PriorityOrdered的BeanPostProcessor
        sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
 
        // 2、排序并注册实现了Ordered的BeanPostProcessor
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : orderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            orderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        sortPostProcessors(beanFactory, orderedPostProcessors);
        registerBeanPostProcessors(beanFactory, orderedPostProcessors);
 
        // 3、排序并注册了剩余的BeanPostProcessor
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : nonOrderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
 
        // 4、排序并注册了实现了MergedBeanDefinitionPostProcessor的BeanPostProcessor
        sortPostProcessors(beanFactory, internalPostProcessors);
        registerBeanPostProcessors(beanFactory, internalPostProcessors);
 
        /**
         * 经过上述四个步骤后，所有的BeanPostProcessor就以有序的形式保存到了beanFactory中
         * 在每个bean实例化时，就能按照这个有序的顺序进行逐个执行BeanPostProcessor的前后置方法了
         */
 
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }

• initMessageSource

    protected void initMessageSource() {
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        /**
         * 从beanFactory中查找messageSource，
         * 若没有则会实例化一个DelegatingMessageSource并注册到beanFactory
         */
        if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
            this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
            if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
                HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
                if (hms.getParentMessageSource() == null) {
                    hms.setParentMessageSource(getInternalParentMessageSource());
                }
            }
        } else {
            DelegatingMessageSource dms = new DelegatingMessageSource();
            dms.setParentMessageSource(getInternalParentMessageSource());
            this.messageSource = dms;
            beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
        }
    }

• initApplicationEventMulticaster

    protected void initApplicationEventMulticaster() {
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        /**
         * 从beanFactory中查找applicationEventMulticaster，
         * 若没有则会初始化一个SimpleApplicationEventMulticaster并注册到beanFactory
         */
        if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
            this.applicationEventMulticaster = beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME,
                    ApplicationEventMulticaster.class);
        } else {
            this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
            beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
        }
    }

• onRefresh

该方法在AbstractApplicationContext中是一个抽象方法

     protected void onRefresh() throws BeansException {
        // For subclasses: do nothing by default.
    }

查看了若干个子类，如AbstractRefreshableWebApplicationContext、GenericWebApplicationContext等，发现其实现中基本都是做的同一件事，初始化了一个themeSource。

    protected void onRefresh() {
        this.themeSource = UiApplicationContextUtils.initThemeSource(this);
    }

但是SpringBoot中onRefresh就非常重要了，内嵌的tomcat容器就是通过该方法创建的。

• registerListeners

    protected void registerListeners() {
        // 首先将所有已添加的监听器绑定到事件广播器中
        for (ApplicationListener<?> listener : getApplicationListeners()) {
            getApplicationEventMulticaster().addApplicationListener(listener);
        }
 
        // 然后再从beanFactory中获取所有ApplicationListener，将beanName绑定到事件广播器中
        String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
        for (String listenerBeanName : listenerBeanNames) {
            getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
        }
 
        // 判断早期的应用事件，若不为空，则调用事件广播器逐个进行广播
        Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
        this.earlyApplicationEvents = null;
        if (earlyEventsToProcess != null) {
            for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
                getApplicationEventMulticaster().multicastEvent(earlyEvent);
            }
        }
    }

• finishBeanFactoryInitialization

    protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        /**
         * 如果conversionService存在的话，则实例化conversionService，
         * 这是一个用于类型转换的组件，不论是ioc的依赖注入还是springmvc的入参绑定都可能会用到该组件
         */
        if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME)
                && beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
            beanFactory
                    .setConversionService(beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
        }
 
        /**
         * 若beanFactory内没有内嵌的值解析器，则默认添加一个内置解析器，但是该内置解析器只能处理系统变量的解析，
         * 但是若配置了PropertySourcesPlaceholderConfigurer，
         * 则会另加入一个读取对应配置文件的值解析器，则默认值解析器就不会再添加到容器了
         * 同时需要注意的是这个值解析器是和当前容器绑定的，也就是说子容器是无法获取到父容器的值解析器的，
         * 这也就是为什么在springmvc的controller中使用@Value是无法注入配置文件中的值的
         */
        if (!beanFactory.hasEmbeddedValueResolver()) {
            beanFactory.addEmbeddedValueResolver(new StringValueResolver() {
                @Override
                public String resolveStringValue(String strVal) {
                    return getEnvironment().resolvePlaceholders(strVal);
                }
            });
        }
 
        // 提早实例化所有LoadTimeWeaverAware实现
        String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
        for (String weaverAwareName : weaverAwareNames) {
            getBean(weaverAwareName);
        }
 
        // 禁止在类型匹配中使用临时的类加载器
        beanFactory.setTempClassLoader(null);
 
        /**
         * 允许缓存beanDefinition元数据，
         * 实则是将所有beanDefinitionNames转化成了String数组，并存储到frozenBeanDefinitionNames中
         */
        beanFactory.freezeConfiguration();
 
        /**
         * 开始实例化所有非延迟加载的单例bean 也就是说会对容器内所有非抽象、非延迟加载的单例bean进行逐个实例化
         */
        beanFactory.preInstantiateSingletons();
    }

• finishRefresh