在前面的文章中，我们主要分析了BeanFactory容器的创建和加载bean的过程，从今天起，我们来分析spring的高级容器ApplicationContext。ApplicationContext包含了BeanFactory的所有功能，并在其原有基础之上，做了很多扩展功能。

1.使用方式

@Test
public void test1() {
    ApplicationContext context = new ClassPathXmlApplicationContext("day12.xml");
    Cat cat = context.getBean("cat", Cat.class);
    cat.sayHello();
    cat.sayArrayNames();
    cat.sayListNames();
    cat.sayMapNames();
    cat.sayPropertiesNames();
    cat.saySetNames();
}

与XmlBeanFactory不同，ClassPathXmlApplicationContext只需要指定配置文件名称即可。

2.ClassPathXmlApplicationContext创建过程

public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
	this(new String[] {configLocation}, true, null);
}

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) throws BeansException {
	// 调用父类构造器
	super(parent);
	// 设定配置文件路径
	setConfigLocations(configLocations);
	if (refresh) {
		// 扩展功能
		refresh();
	}
}

ClassPathXmlApplicationContext对象的创建过程可以分为三个步骤，依次向上调用父类构造器，设定配置文件位置，功能扩展，其中refresh()方法是ApplicationContext最关键最核心的方法。前两者的功能其实我们在之前都已经分析过很多，大家可以自行跟踪代码查看，我们重点分析refresh()方法。

3. 功能扩展

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        // 准备刷新上下文环境
        prepareRefresh();
        // Tell the subclass to refresh the internal bean factory.
        // 读取xml并初始化BeanFactory
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
        // Prepare the bean factory for use in this context.
        // 填充BeanFactory功能
        prepareBeanFactory(beanFactory);
        try {
            // Allows post-processing of the bean factory in context subclasses.
            // 子类覆盖方法额外处理(空方法)
            postProcessBeanFactory(beanFactory);
            // Invoke factory processors registered as beans in the context.
            // 调用各种BeanFactory处理器
            invokeBeanFactoryPostProcessors(beanFactory);
            // Register bean processors that intercept bean creation.
            // 注册拦截Bean创建的Bean处理器
            registerBeanPostProcessors(beanFactory);
            // Initialize message source for this context.
            // 初始化Message资源
            initMessageSource();
            // Initialize event multicaster for this context.
            // 初始化应用消息广播器
            initApplicationEventMulticaster();
            // Initialize other special beans in specific context subclasses.
            // 留给子类初始化其他Bean
            onRefresh();
            // Check for listener beans and register them.
            // 在所有注册Bean中查找Listener Bean,并注册到消息广播器中
            registerListeners();
            // Instantiate all remaining (non-lazy-init) singletons.
            // 初始化剩下的单例Bean(非延迟加载的)
            finishBeanFactoryInitialization(beanFactory);
            // Last step: publish corresponding event.
            // 完成刷新过程,通知生命周期处理器lifecycleProcessor刷新过程,同时发出ContextRefreshEvent通知别人
            finishRefresh();
        }
        catch (BeansException ex) {
            // Destroy already created singletons to avoid dangling resources.
            // 销毁已经创建的Bean
            destroyBeans();
            // Reset 'active' flag.
            // 重置容器激活标签
            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();
        }
    }
}

我们对refres()方法中的的注释，逐条分析。

4.准备刷新上下文环境

/**
 * 准备刷新上下文环境，设置它的启动日期和活动标志，以及执行任何属性源的初始化。
 * Prepare this context for refreshing, setting its startup date and
 * active flag as well as performing any initialization of property sources.
 */
protected void prepareRefresh() {
    this.startupDate = System.currentTimeMillis();
    this.closed.set(false);
    this.active.set(true);

    // Initialize any placeholder property sources in the context environment
    // 在上下文环境中初始化任何占位符属性源。(空的方法,留给子类覆盖)
    initPropertySources();

    // Validate that all properties marked as required are resolvable
    // see ConfigurablePropertyResolver#setRequiredProperties
    // 验证需要的属性文件是否都已放入环境中
    getEnvironment().validateRequiredProperties();

    // Allow for the collection of early ApplicationEvents,
    // to be published once the multicaster is available...
    // 允许收集早期的应用程序事件，一旦有了多播器，就可以发布……
    this.earlyApplicationEvents = new LinkedHashSet<>();
}

该方法中主要设置了启动日期和活动标志，以及执行任何属性源的初始化。

5.读取xml并初始化BeanFactory

该实现过程和Spring之前的版本还是有很大的区别的，我们来看具体的实现代码。

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	// 刷新BeanFactory
	refreshBeanFactory();
	// 获取BeanFactory并返回
	return getBeanFactory();
}

先来看refreshBeanFactory过程。

/**
 * 此实现对上下文的基础bean工厂执行实际的刷新，
 * 关闭前一个bean工厂(如果有的话)和为上下文生命周期的下一个阶段初始化一个新的bean工厂。
 * This implementation performs an actual refresh of this context's underlying
 * bean factory, shutting down the previous bean factory (if any) and
 * initializing a fresh bean factory for the next phase of the context's lifecycle.
 */
@Override
protected final void refreshBeanFactory() throws BeansException {
    // 如果BeanFactory的实例已经存在,则销毁并关闭
    if (hasBeanFactory()) {
        destroyBeans();
        closeBeanFactory();
    }
    // 重新创建BeanFactory
    try {
        // 创建BeanFactory
        DefaultListableBeanFactory beanFactory = createBeanFactory();
        // 为BeanFactory设置id
        beanFactory.setSerializationId(getId());
        // 定制beanFactory
        customizeBeanFactory(beanFactory);
        // 加载BeanDefinition
        loadBeanDefinitions(beanFactory);
        synchronized (this.beanFactoryMonitor) {
            this.beanFactory = beanFactory;
        }
    }
    catch (IOException ex) {
        throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
    }
}

获取BeanFactory

@Override
public final ConfigurableListableBeanFactory getBeanFactory() {
    synchronized (this.beanFactoryMonitor) {
        if (this.beanFactory == null) {
            throw new IllegalStateException("BeanFactory not initialized or already closed - " +
                    "call 'refresh' before accessing beans via the ApplicationContext");
        }
        return this.beanFactory;
    }
}

该过程中最关键的部分就是对BeanDefinition的加载，在分析BeanFactory的章节中，已经做过介绍，这里不再赘述。

6.填充BeanFactory功能

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    // Tell the internal bean factory to use the context's class loader etc.
    // 设置beanFactory的classLoader
    beanFactory.setBeanClassLoader(getClassLoader());
    // 设置beanFactory的表达式语言处理器,Spring3开始增加了对语言表达式的支持,默认可以使用#{bean.xxx}的形式来调用相关属性值
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    // 为beanFactory增加一个默认的propertyEditor,这个主要是对bean的属性等设置管理的一个工具
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

    // Configure the bean factory with context callbacks.
    // 添加ApplicationContextAwareProcessor
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

    // 设置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);

    // BeanFactory interface not registered as resolvable type in a plain factory.
    // MessageSource registered (and found for autowiring) as a bean.
    // 设置几个自动装配的特殊规则
    beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
    beanFactory.registerResolvableDependency(ResourceLoader.class, this);
    beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
    beanFactory.registerResolvableDependency(ApplicationContext.class, this);

    // Register early post-processor for detecting inner beans as ApplicationListeners.
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

    // Detect a LoadTimeWeaver and prepare for weaving, if found.
    // 增加对AspectJ的支持
    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()));
    }

    // Register default environment beans.
    // 注册默认的系统环境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());
    }
}

7.调用各种BeanFactory处理器

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    //getBeanFactoryPostProcessors->获取手动注册的BeanFactoryPostProcessor
    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()));
    }
}

调用工作委托给了PostProcessorRegistrationDelegate类来执行，并且通过getBeanFactoryPostProcessors方法获取了手动注册的BeanFactoryPostProcessor。

该过程优先处理手工注册的处理器，然后再处理通过配置文件注册的处理器；优先处理BeanDefinitionRegistryPostProcessor处理器，然后再处理BeanFactoryPostProcessor处理器，来看一下代码

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public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

    // Invoke BeanDefinitionRegistryPostProcessors first, if any.
    // 首先调用BeanDefinitionRegistryPostProcessors
    // 定义一个变量保存所有的beanFactoryPostProcessors
    Set<String> processedBeans = new HashSet<>();

    // beanFactory是BeanDefinitionRegistry类型
    if (beanFactory instanceof BeanDefinitionRegistry) {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        // 定义BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
        // 定义BeanDefinitionRegistryPostProcessor集合
        List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

        // 循环手动注册的beanFactoryPostProcessors
        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
            // 如果是BeanDefinitionRegistryPostProcessor的实例话,则调用其postProcessBeanDefinitionRegistry方法,对bean进行注册操作
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                // 如果是BeanDefinitionRegistryPostProcessor类型,则直接调用其postProcessBeanDefinitionRegistry
                BeanDefinitionRegistryPostProcessor registryProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor;
                registryProcessor.postProcessBeanDefinitionRegistry(registry);
                registryProcessors.add(registryProcessor);
            }
            // 否则则将其当做普通的BeanFactoryPostProcessor处理,直接加入regularPostProcessors集合,以备后续处理
            else {
                regularPostProcessors.add(postProcessor);
            }
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the bean factory post-processors apply to them!
        // Separate between BeanDefinitionRegistryPostProcessors that implement
        // PriorityOrdered, Ordered, and the rest.
        List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

        // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
        // 首先调用实现了PriorityOrdered(有限排序接口)的BeanDefinitionRegistryPostProcessors
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        // 排序
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        // 加入registryProcessors集合
        registryProcessors.addAll(currentRegistryProcessors);
        // 调用所有实现了PriorityOrdered的的BeanDefinitionRegistryPostProcessors的postProcessBeanDefinitionRegistry方法,注册bean
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 清空currentRegistryProcessors,以备下次使用
        currentRegistryProcessors.clear();

        // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
        // 其次,调用实现了Ordered(普通排序接口)的BeanDefinitionRegistryPostProcessors
        postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
            if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        // 排序
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        // 加入registryProcessors集合
        registryProcessors.addAll(currentRegistryProcessors);
        // 调用所有实现了PriorityOrdered的的BeanDefinitionRegistryPostProcessors的postProcessBeanDefinitionRegistry方法,注册bean
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 清空currentRegistryProcessors,以备下次使用
        currentRegistryProcessors.clear();

        // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
        // 最后,调用其他的BeanDefinitionRegistryPostProcessors
        boolean reiterate = true;
        while (reiterate) {
            reiterate = false;
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            for (String ppName : postProcessorNames) {
                if (!processedBeans.contains(ppName)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                    reiterate = true;
                }
            }
            // 排序
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            // 加入registryProcessors集合
            registryProcessors.addAll(currentRegistryProcessors);
            // 调用其他的BeanDefinitionRegistryPostProcessors的postProcessBeanDefinitionRegistry方法,注册bean
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            // 清空currentRegistryProcessors,以备下次使用
            currentRegistryProcessors.clear();
        }

        // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
        // 调用所有BeanDefinitionRegistryPostProcessor(包括手动注册和通过配置文件注册)
        // 和BeanFactoryPostProcessor(只有手动注册)的回调函数-->postProcessBeanFactory
        invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
        invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    }

    // 如果不是BeanDefinitionRegistry的实例,那么直接调用其回调函数即可-->postProcessBeanFactory
    else {
        // Invoke factory processors registered with the context instance.
        invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }

    // Do not initialize FactoryBeans here: We need to leave all regular beans
    // uninitialized to let the bean factory post-processors apply to them!
    // 上面的代码已经处理完了所有的BeanDefinitionRegistryPostProcessors和手动注册的BeanFactoryPostProcessor
    // 接下来要处理通过配置文件注册的BeanFactoryPostProcessor
    // 首先获取所有的BeanFactoryPostProcessor(注意:这里获取的集合会包含BeanDefinitionRegistryPostProcessors)
    String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

    // Separate between BeanFactoryPostProcessors that implement PriorityOrdered, Ordered, and the rest.
    // 这里,将实现了PriorityOrdered,Ordered的处理器和其他的处理器区分开来,分别进行处理
    // PriorityOrdered有序处理器
    List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    // Ordered有序处理器
    List<String> orderedPostProcessorNames = new ArrayList<>();
    // 无序处理器
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    for (String ppName : postProcessorNames) {
        // 判断processedBeans是否包含当前处理器(processedBeans中的处理器已经被处理过);如果包含,则不做任何处理
        if (processedBeans.contains(ppName)) {
            // skip - already processed in first phase above
        }
        else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            // 加入到PriorityOrdered有序处理器集合
            priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
        }
        else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            // 加入到Ordered有序处理器集合
            orderedPostProcessorNames.add(ppName);
        }
        else {
            // 加入到无序处理器集合
            nonOrderedPostProcessorNames.add(ppName);
        }
    }

    // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
    // 首先调用实现了PriorityOrdered接口的处理器
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

    // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
    // 其次,调用实现了Ordered接口的处理器
    List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
    for (String postProcessorName : orderedPostProcessorNames) {
        orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    sortPostProcessors(orderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

    // Finally, invoke all other BeanFactoryPostProcessors.
    // 最后,调用无序处理器
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

    // Clear cached merged bean definitions since the post-processors might have
    // modified the original metadata, e.g. replacing placeholders in values...
    // 清理元数据
    beanFactory.clearMetadataCache();
}

该篇的篇幅的已经比较大了，剩下的处理，我们在下一个小节再说明。