Spring系列（三）：Spring IoC源碼解析

1、Spring容器類繼承圖

2、容器前期準備

　　IoC源碼解析入口：

/**
 * @desc: ioc原理解析 啓動
 * @author: toby
 * @date: 2019/7/22 22:20
 */
public class PrincipleMain {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(PrincipleConfig.class);
    }
}

　　調用構造函數AnnotationConfigApplicationContext

　　調用this()，會默認先調用父類的無參構造函數，爲ApplicationContext上下文對象初始beanFactory = new DefaultListableBeanFactory()

　　在調用當前類的this()，也就是調用本身的無參構造函數：

　　　　進到建立註解模式下的Bean定義讀取器：

　　org.springframework.context.annotation.AnnotationConfigUtils#registerAnnotationConfigProcessors(org.springframework.beans.factory.support.BeanDefinitionRegistry, java.lang.Object) 主要是註冊Spring自身的一些後置處理器

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
            BeanDefinitionRegistry registry, @Nullable Object source) {

        DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
        if (beanFactory != null) {
            if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
                beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
            }
            if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
                beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
            }
        }

        Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);

        /**
         * 爲咱們容器中註冊解析主配置類的後置處理器ConfigurationClassPostProcessor
         * beanName = org.springframework.context.annotation.internalConfigurationAnnotationProcessor
         */
        if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        /**
         * 爲咱們容器中註冊處理@Autowired註解的Bean的後置處理器AutowiredAnnotationBeanPostProcessor
         * beanName = org.springframework.context.annotation.internalAutowiredAnnotationProcessor
         */
        if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        /**
         * 爲咱們容器中註冊處理@Required屬性註解的Bean後置處理器RequiredAnnotationBeanPostProcessor
         * beanName = org.springframework.context.annotation.internalRequiredAnnotationProcessor
         */
        if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        /**
         * 爲咱們容器註冊處理JSR規範註解的Bean後置處理器CommonAnnotationBeanPostProcessor
         * beanName = org.springframework.context.annotation.internalCommonAnnotationProcessor
         */
        if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        /**
         * 爲咱們容器註冊處理jpa的Bean的後置處理器org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor
         */
        if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition();
            try {
                def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
                        AnnotationConfigUtils.class.getClassLoader()));
            }
            catch (ClassNotFoundException ex) {
                throw new IllegalStateException(
                        "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
            }
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        /**
         * 處理監聽方法的註解解析器EventListenerMethodProcessor
         */
        if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
        }

        /**
         * 註冊事件監聽器工廠
         */
        if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
        }

        return beanDefs;
    }

　　讀取器初始化完成後，Spring的容器的Bean的定義信息就有Spring自身的一些後置處理器了，Debug以下：

　　讀取器初始化完成後，接下來初始化ClassPath下的Bean定義掃描器：

　　　　　org.springframework.context.annotation.ClassPathBeanDefinitionScanner#ClassPathBeanDefinitionScanner(org.springframework.beans.factory.support.BeanDefinitionRegistry, boolean, org.springframework.core.env.Environment, org.springframework.core.io.ResourceLoader) 類路徑下的Bean定義掃描

 

 　　org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider#registerDefaultFilters 注入默認的Filter

protected void registerDefaultFilters() {
        this.includeFilters.add(new AnnotationTypeFilter(Component.class));
        ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
        try {
            this.includeFilters.add(new AnnotationTypeFilter(
                    ((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
            logger.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
        }
        catch (ClassNotFoundException ex) {
            // JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
        }
        try {
            this.includeFilters.add(new AnnotationTypeFilter(
                    ((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));
            logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
        }
        catch (ClassNotFoundException ex) {
            // JSR-330 API not available - simply skip.
        }
    }

　　這裏須要注意的是爲何new AnnotationTypeFilter(Component.class)就能夠處理@Repository，@Service，@Controller這3個註解，緣由以下：

　　自此前期準備工做完成

3、org.springframework.context.support.AbstractApplicationContext#refresh 12大步

public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            //1:準備刷新上下文環境
            prepareRefresh();

            //2:獲取初始化Bean工廠
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            //3:對bean工廠進行填充屬性
            prepareBeanFactory(beanFactory);

            try {
                //4:Spring開放接口 留給子類去實現該接口
                postProcessBeanFactory(beanFactory);

                //5:調用咱們的bean工廠的後置處理器
                invokeBeanFactoryPostProcessors(beanFactory);

                //6:註冊咱們bean後置處理器
                registerBeanPostProcessors(beanFactory);

                //7:初始化國際化資源處理器
                initMessageSource();

                //8:初始化事件多播器
                initApplicationEventMulticaster();

                //9:這個方法一樣也是留個子類實現,其中springboot也是從這個方法進行tomcat的啓動
                onRefresh();

                //10:把咱們的事件監聽器註冊到多播器上
                registerListeners();

                //11:實例化全部的非懶加載的單實例bean
                finishBeanFactoryInitialization(beanFactory);

                //12:最後刷新容器 發佈刷新事件(Spring cloud eureka也是從這裏啓動的)
                finishRefresh();
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }

            finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

　　第一步：prepareRefresh()

　　準備刷新上下文環境：

protected void prepareRefresh() {
        // Switch to active.
        this.startupDate = System.currentTimeMillis();
        this.closed.set(false);
        this.active.set(true);

        if (logger.isInfoEnabled()) {
            logger.info("Refreshing " + this);
        }

        /**
         * 初始化上下文環境
         */
        initPropertySources();

        /**
         * 用來校驗咱們容器啓動必須依賴的環境變量的值
         */
        getEnvironment().validateRequiredProperties();

        /**
         * 建立一個早期事件監聽器對象
         */
        if (this.earlyApplicationListeners == null) {
            this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
        }
        else {
            // Reset local application listeners to pre-refresh state.
            this.applicationListeners.clear();
            this.applicationListeners.addAll(this.earlyApplicationListeners);
        }

        /**
         * 建立一個容器用於保存早期待發布的事件集合 什麼是早期事件了?
         * 就是咱們的事件監聽器尚未註冊到事件多播器上的時候都稱爲早期事件
         */
        this.earlyApplicationEvents = new LinkedHashSet<>();
    }

　　第二步：ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory() 

　　獲取初始化的Bean的工廠：

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        //刷新bean工廠()
        refreshBeanFactory();
        //返回以前容器準備工做的時候建立的的bean工廠也就是DefaultListableBeanFactory（很重要）
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }

　　org.springframework.context.support.GenericApplicationContext#refreshBeanFactory，注意只能刷一次

protected final void refreshBeanFactory() throws IllegalStateException {
        //因爲BeanFactory只能刷新一次，多線程狀況下可能致使線程安全問題，全部使用cas原子操做來保證
        if (!this.refreshed.compareAndSet(false, true)) {
            throw new IllegalStateException(
                    "GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
        }
        //指定Bean工廠的序列化Id
        this.beanFactory.setSerializationId(getId());
    }

 　　第三步：prepareBeanFactory(beanFactory)

　　對bean工廠進行填充屬性：

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        //設置bean工廠的類加載器爲當前application應用上下文的加載器
        beanFactory.setBeanClassLoader(getClassLoader());
        //爲bean工廠設置SPEL表達式解析器對象StandardBeanExpressionResolver
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        //爲咱們的bean工廠設置了一個propertyEditor屬性資源編輯器對象(用於後面的給bean對象賦值使用)
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
        //註冊ApplicationContextAwareProcessor後置處理器用來處理ApplicationContextAware接口的回調方法
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        /**
         * 當Spring將ApplicationContextAwareProcessor註冊後，那麼在invokeAwarelnterfaces方法中調用的Aware類已經不是普通的bean了 ，
         * 如ResourceLoaderAware、ApplicationEventPublisherAware、ApplicationContextAware等，那麼固然須要在Spring作bean的依賴注入的時候忽略它們。
         * 這個就是ignoreDependencyInterface的做用
         */
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
        /**
         * 註冊了依賴解析，例如當註冊BeanFactory.class的解析依賴後，
         * 當bean的屬性注入的時候，一旦檢測到屬性爲BeanFactory類型便會將beanFactory的實例注入進去。
         */
        beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
        beanFactory.registerResolvableDependency(ResourceLoader.class, this);
        beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
        beanFactory.registerResolvableDependency(ApplicationContext.class, this);
        //註冊了一個事件監聽器探測器後置處理器接口
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
        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()));
        }
        if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
        }
        if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
            beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
        }
    }

　　第四步：postProcessBeanFactory(beanFactory)

　　Spring開放接口留給子類去實現該接口：主要用來改變BeanFactory好比給BeanFactory添加一些本身的BeanPostProcessor（Bean的後置處理器）

　　第五步：invokeBeanFactoryPostProcessors(beanFactory)

　　調用咱們的bean工廠的後置處理器：詳解見：Spring IoC源碼解析之invokeBeanFactoryPostProcessors

　　第六步：registerBeanPostProcessors(beanFactory)

　　註冊咱們bean後置處理器：

org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors(org.springframework.beans.factory.config.ConfigurableListableBeanFactory, org.springframework.context.support.AbstractApplicationContext)

/**
     * 往容器中註冊了咱們的bean的後置處理器
     * bean的後置處理器在何時進行調用？在bean的生命週期中
     * @param beanFactory
     * @param applicationContext
     */
    public static void registerBeanPostProcessors(
            ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

        //去容器中獲取全部的BeanPostProcessor的bean名稱
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

        /**
         * beanFactory.getBeanPostProcessorCount()獲取的是已經添加在beanFactory的beanPostProcessors集合中的
         * postProcessorNames.length  beanFactory工廠中BeanPostProcessor個數 +1 又註冊了BeanPostProcessorChecker的後置處理器
         */
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

        /**
         * 按照BeanPostProcessor實現的優先級接口來分離咱們的後置處理器
         */
        //保存實現了priorityOrdered接口的
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
        //容器內部的
        List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
        //實現了咱們ordered接口的
        List<String> orderedPostProcessorNames = new ArrayList<>();
        //實現了咱們任何優先級的
        List<String> nonOrderedPostProcessorNames = new ArrayList<>();
        //循環咱們的bean定義(BeanPostProcessor)
        for (String ppName : postProcessorNames) {
            //若實現了PriorityOrdered接口的
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                //顯示的調用getBean流程建立bean的後置處理器
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                //加入到集合中
                priorityOrderedPostProcessors.add(pp);
                //判斷是否實現了MergedBeanDefinitionPostProcessor
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    //加入到集合中
                    internalPostProcessors.add(pp);
                }
            }
            //判斷是否實現了Ordered
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        //把實現了priorityOrdered註冊到容器中
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

        //處理實現Ordered的bean後置處理器
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
        for (String ppName : orderedPostProcessorNames) {
            //顯示調用getBean方法
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            //加入到集合中
            orderedPostProcessors.add(pp);
            //判斷是否實現了MergedBeanDefinitionPostProcessor
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                //加入到集合中
                internalPostProcessors.add(pp);
            }
        }
        //排序而且註冊咱們實現了Order接口的後置處理器
        sortPostProcessors(orderedPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, orderedPostProcessors);

        // 實例化咱們全部的非排序接口的
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
        for (String ppName : nonOrderedPostProcessorNames) {
            //顯示調用
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            //判斷是否實現了MergedBeanDefinitionPostProcessor
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        //註冊咱們普通的沒有實現任何排序接口的
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

        //註冊MergedBeanDefinitionPostProcessor類型的後置處理器
        sortPostProcessors(internalPostProcessors, beanFactory);
        registerBeanPostProcessors(beanFactory, internalPostProcessors);

        //註冊ApplicationListenerDetector應用監聽器探測器的後置處理器
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }

　　第七步：initMessageSource()

　　初始化國際化資源處理器：

/**
     * Initialize the MessageSource.
     * Use parent's if none defined in this context.
     */
    protected void initMessageSource() {
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
            this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
            // Make MessageSource aware of parent MessageSource.
            if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
                HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
                if (hms.getParentMessageSource() == null) {
                    // Only set parent context as parent MessageSource if no parent MessageSource
                    // registered already.
                    hms.setParentMessageSource(getInternalParentMessageSource());
                }
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Using MessageSource [" + this.messageSource + "]");
            }
        }
        else {
            // Use empty MessageSource to be able to accept getMessage calls.
            DelegatingMessageSource dms = new DelegatingMessageSource();
            dms.setParentMessageSource(getInternalParentMessageSource());
            this.messageSource = dms;
            beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
            if (logger.isDebugEnabled()) {
                logger.debug("Unable to locate MessageSource with name '" + MESSAGE_SOURCE_BEAN_NAME +
                        "': using default [" + this.messageSource + "]");
            }
        }
    }

　　第八步：initApplicationEventMulticaster()

　　初始化事件多播器：

/**
     * 從bean工廠中獲取或者直接顯示的new一個事件多播器賦值給applicatoinContext對象的applicationEventMulticaster屬性
     * 事件多播器採用典型的設計模式就是觀察者模式 多播器做爲的是一個被觀察者
     * @see org.springframework.context.event.SimpleApplicationEventMulticaster
     */
    protected void initApplicationEventMulticaster() {
        //獲取咱們的bean工廠對象
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        //判斷容器中是否包含了applicationEventMulticaster事件多播器組件
        if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
            //直接顯示的調用咱們的getBean獲取出來賦值給咱們的applicationContext對象
            this.applicationEventMulticaster =
                    beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
            if (logger.isDebugEnabled()) {
                logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
            }
        }
        //容器中沒有的話
        else {
            //直接new一個
            this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
            //而且注入到容器中
            beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
            if (logger.isDebugEnabled()) {
                logger.debug("Unable to locate ApplicationEventMulticaster with name '" +
                        APPLICATION_EVENT_MULTICASTER_BEAN_NAME +
                        "': using default [" + this.applicationEventMulticaster + "]");
            }
        }
    }

　　第九步：onRefresh()

　　這個方法很重要一樣也是留個子類實現,其中Spring Boot就是從這個方法進行tomcat的啓動（後續講Spring Boot的源碼分析的時候會涉及到這塊，好比：Spring容器的啓動如何帶動web容器tomcat的啓動以及web容器tomcat的啓動如何帶動Spring容器的啓動）

　　第十步：registerListeners()

　　把咱們的事件監聽器註冊到事件多播器上：

protected void registerListeners() {
        //獲取容器中全部的監聽器對象
        for (ApplicationListener<?> listener : getApplicationListeners()) {
            //把監聽器挨個的註冊到咱們的事件多播器上去
            getApplicationEventMulticaster().addApplicationListener(listener);
        }

        //獲取bean定義中的監聽器對象
        String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
        //把監聽器的名稱註冊到咱們的事件多播器上
        for (String listenerBeanName : listenerBeanNames) {
            getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
        }

        //在這裏獲取咱們的早期事件
        Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
        this.earlyApplicationEvents = null;
        if (earlyEventsToProcess != null) {
            //經過多播器進行播發早期事件
            for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
                getApplicationEventMulticaster().multicastEvent(earlyEvent);
            }
        }
    }

　　如何發佈事件，經過事件多播器方法：multicastEvent(ApplicationEvent event)，進入方法

@Override
    public void multicastEvent(ApplicationEvent event) {
        multicastEvent(event, resolveDefaultEventType(event));
    }

　　multicastEvent(event, resolveDefaultEventType(event))方法：

@Override
    public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
        ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
        //從事件多播器中獲取出全部的監聽器
        for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
            //判斷多播器中是否支持異步多播的
            Executor executor = getTaskExecutor();
            if (executor != null) {
                //異步播發事件
                executor.execute(() -> invokeListener(listener, event));
            }
            else {//同步播發
                invokeListener(listener, event);
            }
        }
    }

　　invokeListener(listener, event)方法：

/**
     * Invoke the given listener with the given event.
     * @param listener the ApplicationListener to invoke
     * @param event the current event to propagate
     * @since 4.1
     */
    protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
        ErrorHandler errorHandler = getErrorHandler();
        if (errorHandler != null) {
            try {
                doInvokeListener(listener, event);
            }
            catch (Throwable err) {
                errorHandler.handleError(err);
            }
        }
        else {
            doInvokeListener(listener, event);
        }
    }

　　doInvokeListener(ApplicationListener listener, ApplicationEvent event) 方法（Spring有一個特色涉及到以do開頭的方法都是真正幹活的）：

　　第十一步：finishBeanFactoryInitialization(beanFactory)

 　　實例化全部的非懶加載的單實例bean：詳解見：Spring IoC源碼解析之getBean

　　第十二步：finishRefresh()

　　最後刷新容器發佈刷新事件(Spring cloud eureka也是從這裏啓動的)：

protected void finishRefresh() {

        //初始化生命週期處理器
        initLifecycleProcessor();

        //調用生命週期處理器的onRefresh方法
        getLifecycleProcessor().onRefresh();

        //發佈ContextRefreshedEvent事件
        publishEvent(new ContextRefreshedEvent(this));

        // Participate in LiveBeansView MBean, if active.
        LiveBeansView.registerApplicationContext(this);
    }

　　① 初始化生命週期處理器：initLifecycleProcessor()方法：

protected void initLifecycleProcessor() {
        //獲取beanFactory工廠
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        //判斷容器中是否有lifecycleProcessor，有就直接從容器中拿
        if (beanFactory.containsLocalBean(LIFECYCLE_PROCESSOR_BEAN_NAME)) {
            this.lifecycleProcessor =
                    beanFactory.getBean(LIFECYCLE_PROCESSOR_BEAN_NAME, LifecycleProcessor.class);
            if (logger.isDebugEnabled()) {
                logger.debug("Using LifecycleProcessor [" + this.lifecycleProcessor + "]");
            }
        }
        //沒有建立一個DefaultLifecycleProcessor，而後註冊到容器中
        else {
            DefaultLifecycleProcessor defaultProcessor = new DefaultLifecycleProcessor();
            defaultProcessor.setBeanFactory(beanFactory);
            this.lifecycleProcessor = defaultProcessor;
            beanFactory.registerSingleton(LIFECYCLE_PROCESSOR_BEAN_NAME, this.lifecycleProcessor);
            if (logger.isDebugEnabled()) {
                logger.debug("Unable to locate LifecycleProcessor with name '" +
                        LIFECYCLE_PROCESSOR_BEAN_NAME +
                        "': using default [" + this.lifecycleProcessor + "]");
            }
        }
    }

　　② 調用生命週期處理器的onRefresh方法：getLifecycleProcessor().onRefresh()：org.springframework.context.support.DefaultLifecycleProcessor#onRefresh：

@Override
    public void onRefresh() {
        startBeans(true);
        this.running = true;
    }

　　startBeans(true)方法：org.springframework.context.support.DefaultLifecycleProcessor#startBeans：主要的功能是找到Spring容器的Lifecycle類型的Bean，而後調用start()去啓動

private void startBeans(boolean autoStartupOnly) {
        Map<String, Lifecycle> lifecycleBeans = getLifecycleBeans();
        Map<Integer, LifecycleGroup> phases = new HashMap<Integer, LifecycleGroup>();
        for (Map.Entry<String, ? extends Lifecycle> entry : lifecycleBeans.entrySet()) {
            Lifecycle bean = entry.getValue();
            if (!autoStartupOnly || (bean instanceof SmartLifecycle && ((SmartLifecycle) bean).isAutoStartup())) {
                int phase = getPhase(bean);
                LifecycleGroup group = phases.get(phase);
                if (group == null) {
                    group = new LifecycleGroup(phase, this.timeoutPerShutdownPhase, lifecycleBeans, autoStartupOnly);
                    phases.put(phase, group);
                }
                group.add(entry.getKey(), bean);
            }
        }
        if (!phases.isEmpty()) {
            List<Integer> keys = new ArrayList<Integer>(phases.keySet());
            Collections.sort(keys);
            for (Integer key : keys) {
                phases.get(key).start();
            }
        }
    }

　　start()方法：

　　doStart(this.lifecycleBeans, member.name, this.autoStartupOnly)方法：

private void doStart(Map<String, ? extends Lifecycle> lifecycleBeans, String beanName, boolean autoStartupOnly) {
        Lifecycle bean = lifecycleBeans.remove(beanName);
        if (bean != null && bean != this) {
            String[] dependenciesForBean = getBeanFactory().getDependenciesForBean(beanName);
            for (String dependency : dependenciesForBean) {
                doStart(lifecycleBeans, dependency, autoStartupOnly);
            }
            //bean不在運行中而且(autoStartupOnly=false 或者 不是SmartLifecycle類型 或者 isAutoStartup() = true)
            if (!bean.isRunning() &&
                    (!autoStartupOnly || !(bean instanceof SmartLifecycle) || ((SmartLifecycle) bean).isAutoStartup())) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Starting bean '" + beanName + "' of type [" + bean.getClass().getName() + "]");
                }
                try {
                    //調用生命週期Lifecycle Bean的start()方法
                    bean.start();
                }
                catch (Throwable ex) {
                    throw new ApplicationContextException("Failed to start bean '" + beanName + "'", ex);
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Successfully started bean '" + beanName + "'");
                }
            }
        }
    }

　　③ 發佈ContextRefreshedEvent事件：主要就是調用前面第八步建立的事件多播器的發佈事件方法getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType)：

protected void publishEvent(Object event, ResolvableType eventType) {
        Assert.notNull(event, "Event must not be null");
        if (logger.isTraceEnabled()) {
            logger.trace("Publishing event in " + getDisplayName() + ": " + event);
        }

        // Decorate event as an ApplicationEvent if necessary
        ApplicationEvent applicationEvent;
        if (event instanceof ApplicationEvent) {
            applicationEvent = (ApplicationEvent) event;
        }
        else {
            applicationEvent = new PayloadApplicationEvent<Object>(this, event);
            if (eventType == null) {
                eventType = ((PayloadApplicationEvent) applicationEvent).getResolvableType();
            }
        }

        // Multicast right now if possible - or lazily once the multicaster is initialized
        if (this.earlyApplicationEvents != null) {
            this.earlyApplicationEvents.add(applicationEvent);
        }
        else {
            getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
        }

        // Publish event via parent context as well...
        if (this.parent != null) {
            if (this.parent instanceof AbstractApplicationContext) {
                ((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
            }
            else {
                this.parent.publishEvent(event);
            }
        }
    }

 　　

　　總結：從Spring IoC的源碼解析過程當中，咱們更加深刻的瞭解容器的初始化，Bean的後置處理器，國際化，事件多播器發佈事件，Bean的建立，屬性的賦值，三級緩存解決循環依賴問題，Lifecycle的做用，Spring場景應用：Spring系列（二）：Spring IoC應用，Spring系列完整代碼在碼雲：spring系列