Spring源码解析之标签的解析下篇

正文

上篇文章我们介绍了Spring默认标签的解析，本文我们来分析一下Spring自定义标签的解析。上篇文章我们了解到Spring的默认标签目前有4个（import、alias、bean、beans），也就是说除了这4个标签以外的标签都是自定义标签（当然这里所说的标签不包括那些以子标签形式存在的如property、value等标签），如我们熟知的事务标签：

<tx:annotation-driven/>

注解扫描标签：

<context:component-scan/>

等都属于自定义标签，下面就让我们来分析一下这些自定义标签是如何解析的，承接上篇文章中自定义标签解析的分支：

public BeanDefinition parseCustomElement(Element ele) {
    /*解析自定义元素*/
    return parseCustomElement(ele, null);
}

public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
    //获取命名空间
    String namespaceUri = getNamespaceURI(ele);
    /*根据命名空间获取NamespaceHandler*/
    NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
    if (handler == null) {
        error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
        return null;
    }
    /*解析自定义标签*/
    return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
}

public NamespaceHandler resolve(String namespaceUri) {
    /*获取所有已经配置的handler映射*/
    Map<String, Object> handlerMappings = getHandlerMappings();
    //根据命名空间找到对应的映射
    Object handlerOrClassName = handlerMappings.get(namespaceUri);
    if (handlerOrClassName == null) {
        return null;
    }
    else if (handlerOrClassName instanceof NamespaceHandler) {
        //如果已经实例化过，直接返回
        return (NamespaceHandler) handlerOrClassName;
    }
    else {
        String className = (String) handlerOrClassName;
        try {
            //反射加载类
            Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
            if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
                throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
                        "] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
            }
            //实例化对象
            NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
            namespaceHandler.init(); //调用init方法
            //放入缓存
            handlerMappings.put(namespaceUri, namespaceHandler);
            return namespaceHandler;
        }
        catch (ClassNotFoundException ex) {
            throw new FatalBeanException("NamespaceHandler class [" + className + "] for namespace [" +
                    namespaceUri + "] not found", ex);
        }
        catch (LinkageError err) {
            throw new FatalBeanException("Invalid NamespaceHandler class [" + className + "] for namespace [" +
                    namespaceUri + "]: problem with handler class file or dependent class", err);
        }
    }
}

private Map<String, Object> getHandlerMappings() {
    if (this.handlerMappings == null) {
        synchronized (this) {
            if (this.handlerMappings == null) {
                try {
                    //加载配置
                    Properties mappings =
                            PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);
                    if (logger.isDebugEnabled()) {
                        logger.debug("Loaded NamespaceHandler mappings: " + mappings);
                    }
                    Map<String, Object> handlerMappings = new ConcurrentHashMap<String, Object>(mappings.size());
                    //放入缓存
                    CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);
                    this.handlerMappings = handlerMappings;
                }
                catch (IOException ex) {
                    throw new IllegalStateException(
                            "Unable to load NamespaceHandler mappings from location [" + this.handlerMappingsLocation + "]", ex);
                }
            }
        }
    }
    return this.handlerMappings;
}

这里就是加载配置文件到内存中，而this.handlerMappingsLocation在调用构造方法初始化时被赋值为META-INF/Spring.handlers，我们来看一下Spring事务自定义标签对应这里的配置，锁定spring-tx包下的META-INF/Spring.handlers：

http\://www.springframework.org/schema/tx=org.springframework.transaction.config.TxNamespaceHandler

所以在解析Spring事务自定义标签时就会找到TxNamespaceHandler并调用其init方法：

public void init() {
    registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
    registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
    registerBeanDefinitionParser("jta-transaction-manager", new JtaTransactionManagerBeanDefinitionParser());
}

init方法就是注册对应三个标签的解析器，这里用Spring事务标签举例，其他自定义标签大同小异。下面就是解析过程：

public BeanDefinition parse(Element element, ParserContext parserContext) {
    /*寻找解析器进行解析*/
    return findParserForElement(element, parserContext).parse(element, parserContext);
}

private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
    //以<tx:annotation-driven/>为例，这里的localName就是annotation-driven
    String localName = parserContext.getDelegate().getLocalName(element);
    //根据localName获取解析器，上面注册过annotation-driven的解析器
    BeanDefinitionParser parser = this.parsers.get(localName);
    if (parser == null) {
        parserContext.getReaderContext().fatal(
                "Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
    }
    return parser;
}

获取到BeanDefinitionParser后，调用其parse方法进行解析，解析的过程就是根据开发者需求的不同自行实现了，整体来说就是解析配置到注册BeanDefinition的过程。到这里自定义标签的解析就完成了，上篇文章开始的refresh方法我们只分析了前两步，下面我们来看后续的步骤：

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    beanFactory.setBeanClassLoader(getClassLoader());
    //设置SPEL表达式处理器，在bean初始化填充属性时会用到
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    //添加属性编辑器注册器
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
    //添加Aware接口的BeanPostProcessor
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
    //设置几个忽略自动装配的接口
    beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
    beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
    beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
    beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
    beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
    beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
    //注册几个自动装配的接口
    beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
    beanFactory.registerResolvableDependency(ResourceLoader.class, this);
    beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
    beanFactory.registerResolvableDependency(ApplicationContext.class, this);
    //添加用于发现ApplicationListener的BeanPostProcessor
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
    //增加对静态AOP的支持
    if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
        beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
        beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    }
    //添加几个默认的系统环境bean
    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());
    }
}

这里提到了属性编辑器和自动装配的概念，这些我们会在bean创建的文章中进行讲解，这里先留一个悬念。简单介绍一下方法中注册的ApplicationContextAwareProcessor，它实现了BeanPostProcessor，Spring会保证所有bean在实例化的时候都会调用其postProcessAfterInitialization方法，我们可以使用这个方法包装和改变bean，我们来看一下这个方法：

public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
    AccessControlContext acc = null;
    if (System.getSecurityManager() != null &&
            (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
                    bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
                    bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
        acc = this.applicationContext.getBeanFactory().getAccessControlContext();
    }
    if (acc != null) {
        AccessController.doPrivileged(new PrivilegedAction<Object>() {
            @Override
            public Object run() {
                invokeAwareInterfaces(bean); /*调用Aware接口*/
                return null;
            }
        }, acc);
    }
    else {
        invokeAwareInterfaces(bean); /*调用Aware接口*/
    }
    return bean;
}

private void invokeAwareInterfaces(Object bean) {
    if (bean instanceof Aware) {
        if (bean instanceof EnvironmentAware) {
            ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
        }
        if (bean instanceof EmbeddedValueResolverAware) {
            ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
        }
        if (bean instanceof ResourceLoaderAware) {
            ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
        }
        if (bean instanceof ApplicationEventPublisherAware) {
            ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
        }
        if (bean instanceof MessageSourceAware) {
            ((MessageSourceAware) bean).setMessageSource(this.applicationContext);
        }
        if (bean instanceof ApplicationContextAware) {
            ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
        }
    }
}

当我们的bean实现了某个Aware接口，这里就会调用相关的set方法为我们的bean设置相关资源。下一步的postProcessBeanFactory默认为空实现，留给子类扩展做BeanFactory初始化后的后置处理。接下来就是调用所有注册的BeanFactoryPostProcessor的相关方法，我们以一个例子来说明一下BeanFactoryPostProcessor的用法，我们在使用Spring整合Mybatis的时候会配置一个类MapperScannerConfigurer，用来扫描我们工程中定义的所有Mapper接口，我们来看一下它的层次结构： 这里就会调用它的postProcessBeanDefinitionRegistry方法来扫描我们配置的包完成Mapper相关的BeanDefinition的注册，我们会在Spring整合Mybatis的文章中进行详细描述。

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    /*调用注册的所有BeanFactoryPostProcessor的相关方法*/
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
    //再次确认是否需要增加对静态AOP的支持，这段逻辑在prepareBeanFactory方法中已经执行过，这里因为有可能有新的BeanDefinition注册，所以需要再次确认
    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) {
    Set<String> processedBeans = new HashSet<String>();
    if (beanFactory instanceof BeanDefinitionRegistry) {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
        List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
                new LinkedList<BeanDefinitionRegistryPostProcessor>();
        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
            //首先调用BeanDefinitionRegistryPostProcessor 
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                BeanDefinitionRegistryPostProcessor registryPostProcessor =
                        (BeanDefinitionRegistryPostProcessor) postProcessor;
                        //执行postProcessBeanDefinitionRegistry方法
                registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
                registryPostProcessors.add(registryPostProcessor);
            }
            else {
                regularPostProcessors.add(postProcessor);
            }
        }
        //从所有注册的BeanDefinition中获取BeanDefinitionRegistryPostProcessor
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
        for (String ppName : postProcessorNames) {
            //首先执行实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessor
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        sortPostProcessors(beanFactory, priorityOrderedPostProcessors); //排序
        registryPostProcessors.addAll(priorityOrderedPostProcessors);
        invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry); //执行postProcessBeanDefinitionRegistry方法
        postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
        for (String ppName : postProcessorNames) {
            //接下来执行实现Ordered接口的BeanDefinitionRegistryPostProcessor
            if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        sortPostProcessors(beanFactory, orderedPostProcessors); //排序
        registryPostProcessors.addAll(orderedPostProcessors);
        invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry); //执行
        boolean reiterate = true;
        while (reiterate) {
            reiterate = false;
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            for (String ppName : postProcessorNames) {
                //执行剩余的BeanDefinitionRegistryPostProcessor
                if (!processedBeans.contains(ppName)) {
                    BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class);
                    registryPostProcessors.add(pp);
                    processedBeans.add(ppName);
                    pp.postProcessBeanDefinitionRegistry(registry);
                    reiterate = true;
                }
            }
        }
        //BeanDefinitionRegistryPostProcessor继承了BeanFactoryPostProcessor，执行完postProcessBeanDefinitionRegistry方法之后还要执行postProcessBeanFactory方法
        invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
        invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    }
    else {
        invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }
    String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
            //剩余的BeanFactoryPostProcessor同样按照实现PriorityOrdered --> 实现Ordered --> 其他的顺序执行
    List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    List<String> orderedPostProcessorNames = new ArrayList<String>();
    List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
    for (String ppName : postProcessorNames) {
        //上面已经将所有的BeanDefinitionRegistryPostProcessor都执行完了，这里要将它们排除掉，执行剩余的BeanFactoryPostProcessor
        if (processedBeans.contains(ppName)) {
        }
        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);
        }
    }
    sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
    List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    for (String postProcessorName : orderedPostProcessorNames) {
        orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    sortPostProcessors(beanFactory, orderedPostProcessors);
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
    beanFactory.clearMetadataCache();
}

下一步是注册BeanPostProcessor：

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    /*注册BeanPostProcessor*/
    PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}

public static void registerBeanPostProcessors(
        ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
        //获取所有BeanPostProcessor的beanName
    String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
    int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
    //注册BeanPostProcessorChecker的作用是在BeanPostProcessor初始化期间有bean被创建了就会打印日志
    beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
    //和上面BeanFactoryPostProcessor执行的过程非常相似，同样是按照PriorityOrdered --> Ordered --> 其他的顺序进行注册，区别是这里最后加了MergedBeanDefinitionPostProcessor类型的BeanPostProcessor的注册，并且这里不会执行相关方法，BeanPostProcessor的相关方法在bean创建时才会执行。这里看起来有重复注册的问题，不过beanFactory.addBeanPostProcessor是先移除在添加，所以不会重复
    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);
        }
    }
    sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
    registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
    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);
    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);
    sortPostProcessors(beanFactory, internalPostProcessors);
    registerBeanPostProcessors(beanFactory, internalPostProcessors);
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
    Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
    this.beanPostProcessors.remove(beanPostProcessor); //先移除
    this.beanPostProcessors.add(beanPostProcessor); //再添加
    if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
        this.hasInstantiationAwareBeanPostProcessors = true;
    }
    if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
        this.hasDestructionAwareBeanPostProcessors = true;
    }
}

下一步是初始化MessageSource，用于国际化处理，关于Spring的国际化处理，有兴趣的读者可以查阅相关资料进行学习，这里就不做描述了。接下来我们来看应用事件广播器的初始化：

protected void initApplicationEventMulticaster() {
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    //用户自定义事件广播器
    if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
        this.applicationEventMulticaster =
                beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
        if (logger.isDebugEnabled()) {
            logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
        }
    }
    else { /*默认事件广播器*/
        this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
        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 + "]");
        }
    }
}

我们以默认事件广播器SimpleApplicationEventMulticaster为例看一下它是如何广播事件的：

public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) {
    ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
    for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
        Executor executor = getTaskExecutor();
        if (executor != null) {
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    /*通知监听器*/
                    invokeListener(listener, event);
                }
            });
        }
        else {
            /*通知监听器*/
            invokeListener(listener, event);
        }
    }
}

protected void invokeListener(ApplicationListener listener, ApplicationEvent event) {
    ErrorHandler errorHandler = getErrorHandler();
    if (errorHandler != null) {
        try {
            //将应用事件通知监听器
            listener.onApplicationEvent(event);
        }
        catch (Throwable err) {
            errorHandler.handleError(err);
        }
    }
    else {
        try {
            //将应用事件通知监听器
            listener.onApplicationEvent(event);
        }
        catch (ClassCastException ex) {
            String msg = ex.getMessage();
            if (msg == null || msg.startsWith(event.getClass().getName())) {
                Log logger = LogFactory.getLog(getClass());
                if (logger.isDebugEnabled()) {
                    logger.debug("Non-matching event type for listener: " + listener, ex);
                }
            }
            else {
                throw ex;
            }
        }
    }
}

很简单，通知监听器就是调用所有监听器的onApplicationEvent方法将事件传入，由监听器自己决定是否处理当前事件，这是一个典型的观察者模式的实现。而接下来就是监听器的注册：

protected void registerListeners() {
    //编码方式的监听器注册
    for (ApplicationListener<?> listener : getApplicationListeners()) {
        getApplicationEventMulticaster().addApplicationListener(listener);
    }
    //配置方式的监听器注册
    String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
    for (String listenerBeanName : listenerBeanNames) {
        getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
    }
    //将提前发布的应用事件通知给所有监听器
    Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
    this.earlyApplicationEvents = null;
    if (earlyEventsToProcess != null) {
        for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
            getApplicationEventMulticaster().multicastEvent(earlyEvent);
        }
    }
}

接下来是初始化所有非lazy-init的bean：

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    //初始化类型转换器
    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));
    }
    //如果没有配置value处理器（例如PropertyPlaceholderConfigurer）则注册一个默认的value处理器，主要用于处理注解的value
    if (!beanFactory.hasEmbeddedValueResolver()) {
        beanFactory.addEmbeddedValueResolver(new StringValueResolver() {
            @Override
            public String resolveStringValue(String strVal) {
                return getEnvironment().resolvePlaceholders(strVal);
            }
        });
    }
    //初始化实现LoadTimeWeaverAware的bean
    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
        getBean(weaverAwareName);
    }
    beanFactory.setTempClassLoader(null);
    //冻结BeanDefinition，到这里BeanDefinition就不能再修改了，下面就要初始化了
    beanFactory.freezeConfiguration();
    /*初始化非lazy-init的单例bean*/
    beanFactory.preInstantiateSingletons();
}

这里提到的类型转换器我们可以通过配置ConversionServiceFactoryBean来注册我们自定义的类型转换器，就是在这里初始化的。

public void preInstantiateSingletons() throws BeansException {
    if (this.logger.isDebugEnabled()) {
        this.logger.debug("Pre-instantiating singletons in " + this);
    }
    //获取所有beanName
    List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
    for (String beanName : beanNames) {
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        //非abstract、非lazy-init的单例bean
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            //FactoryBean的处理
            if (isFactoryBean(beanName)) {
                final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
                boolean isEagerInit;
                if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                    isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
                        @Override
                        public Boolean run() {
                            return ((SmartFactoryBean<?>) factory).isEagerInit();
                        }
                    }, getAccessControlContext());
                }
                else {
                    isEagerInit = (factory instanceof SmartFactoryBean &&
                            ((SmartFactoryBean<?>) factory).isEagerInit());
                }
                if (isEagerInit) {
                    getBean(beanName); //初始化
                }
            }
            else { //普通bean初始化
                getBean(beanName);
            }
        }
    }
    //调用所有初始化的后的回调，Spring4.1的新特性，我们的bean实现了SmartInitializingSingleton后，会在初始化后调用实现的afterSingletonsInstantiated方法，我们可以在里面定义一些bean初始化后需要的逻辑
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {
            final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    @Override
                    public Object run() {
                        smartSingleton.afterSingletonsInstantiated();
                        return null;
                    }
                }, getAccessControlContext());
            }
            else {
                smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

bean初始化的过程我们会在后续的文章中进行详细阐述，下面就是最后一步啦：

protected void finishRefresh() {
    /*初始化LifecycleProcessor（生命周期处理器）*/
    initLifecycleProcessor();
    /*调用onRefresh*/
    getLifecycleProcessor().onRefresh();
    //发送Spring上下文初始化完成事件
    publishEvent(new ContextRefreshedEvent(this));
    //注册MBean
    LiveBeansView.registerApplicationContext(this);
}

protected void initLifecycleProcessor() {
    ConfigurableListableBeanFactory beanFactory = getBeanFactory();
    //用户自定义LifecycleProcessor
    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 + "]");
        }
    }
    else { /*默认LifecycleProcessor*/
        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 + "]");
        }
    }
}

注册完LifecycleProcessor接着会调用它的onRefresh方法，我们以默认的DefaultLifecycleProcessor为例分析一下它的作用：

public void onRefresh() {
    /*实现了Lifecycle的bean处理*/
    startBeans(true);
    this.running = true;
}

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();
        }
    }
}

实现了Lifecycle接口的bean，Spring会保证在启动时调用其start方法，在Spring关闭时调用其stop方法。到这里，整个Spring容器就初始化完成了。

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