Spring IOC（二）容器初始化

本系列目录：

Spring IOC（一）概览

Spring IOC（二）容器初始化

Spring IOC（三）依赖注入

Spring IOC（四）总结

 

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前面一篇概览了IOC容器的接口设计。

本文从ApplicationContext接口的一个实现类ClassPathXmlApplicationContext入手，分析容器初始化过程。先看一下ApplicationContext接口设计：

一、ApplicationContext接口设计

ApplicationContext是spring中较高级的容器。和BeanFactory类似，它可以加载配置文件中定义的bean，当有请求的时候分配bean。 另外，它增加了企业所需要的功能，比如，从属性文件解析文本信息和将事件传递给所指定的监听器。接口设计图如下：

，

ApplicationContext继承5个接口：

1.2个核心接口：

ListableBeanFactory：支持获取bean 工厂的所有bean实例

HierarchicalBeanFactory：支持继承关系

2.3个拓展接口：

MessageSource：提供国际化支持

ApplicationEventPublisher：支持事件驱动模型中的事件发布器，这些事件和Bean的生命周期的结合为Bean的管理提供了便利。

ResourcePatternResolver：资源解析器

 

常见实现类：

1.FileSystemXmlApplicationContext：从指定文件地址的加载xml定义的bean

2.ClassPathXmlApplicationContext：从类路径下载入xml定义的bean

3.XmlWebApplicationContext：web 应用程序的范围内载入xml定义的bean

二、深入源码，看IOC容器初始化

为了方便理解和追踪代码，使用常用实现类ClassPathXmlApplicationContext写了一个小例子，步骤如下：

1）.在类路径下新建xml，定义一个bean,其中daoImpl就是bean的名字，spring.aop.xml.dao.impl.DaoImpl对应具体的一个pojo.

 <bean id="daoImpl" class="spring.aop.xml.dao.impl.DaoImpl" /> 

2）.main方法中直接载入xml,然后获取bean,最后执行bean实例的方法。

    public static void main(String[] args) {
        //源码入口，从类路径下读取xml
        ApplicationContext ac1 = new ClassPathXmlApplicationContext("aop.xml");
        Dao dao = (Dao)ac1.getBean("daoImpl");//根据名称获取Bean
        dao.select();//执行Bean实例方法    
      }

下面我们就分析ClassPathXmlApplicationContext源码，来看看都做了什么。

2.1ClassPathXmlApplicationContext类图

DefaultResourceLoader，该类设置classLoader，并且将配置文件 封装为Resource文件。

AbstractApplicationContext，该类完成了大部分的IOC容器初始化工作，同时也提供了扩展接口留给子类去重载。该类的refresh()函数是核心初始化操作。

AbstractRefreshableApplicationContext，该类支持刷新BeanFactory。

AbstractRefreshableConfigApplicationContext，该类保存了配置文件路径

AbstractXmlApplicationContext：该类支持解析bean定义文件

最后ClassPathXmlApplicationContext:只提供了一个简单的构造函数

Spring 将类职责分开，形成职责链，每一层次的扩展 都只是添加了某个功能

然后父类定义大量的模板，让子类实现，父类层层传递到子类 直到某个子类重载了抽象方法。这里应用到了职责链设计模式和模板设计模式，IOC是个容器工厂设计模式。

 

2.2 回顾上面的小例子，new ClassPathXmlApplicationContext("aop.xml");这行代码做了什么？

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
        throws BeansException {

    super(parent);//把ApplicationContext作为父容器，上述测试类中由于直接载入的xml,没有父容器所以实际传了null
    setConfigLocations(configLocations);//替换${}后设置配置路径
    if (refresh) {
        refresh();//核心方法
    }
}

ClassPathXmlApplicationContext的refresh()实际上就是调用了AbstractApplicationContext的refresh()方法。全方法被synchronized同步块锁住，源码如下：

public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            //准备刷新的上下文环境，例如对系统属性或者环境变量进行准备及验证。
            prepareRefresh();

            //启动子类的refreshBeanFactory方法.解析xml
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            //为BeanFactory配置容器特性，例如类加载器、事件处理器等.
            prepareBeanFactory(beanFactory);

            try {
                //设置BeanFactory的后置处理. 空方法，留给子类拓展用。 
                postProcessBeanFactory(beanFactory);

                //调用BeanFactory的后处理器, 这些后处理器是在Bean定义中向容器注册的.  
                invokeBeanFactoryPostProcessors(beanFactory);

                //注册Bean的后处理器, 在Bean创建过程中调用.  
                registerBeanPostProcessors(beanFactory);

                //初始化上下文中的消息源，即不同语言的消息体进行国际化处理  
                initMessageSource();

                //初始化ApplicationEventMulticaster bean,应用事件广播器
                initApplicationEventMulticaster();

                //初始化其它特殊的Bean， 空方法，留给子类拓展用。 
                onRefresh();

                //检查并向容器注册监听器Bean
                registerListeners();

                //实例化所有剩余的(non-lazy-init) 单例Bean.
                finishBeanFactoryInitialization(beanFactory);

                //发布容器事件, 结束refresh过程. 
                finishRefresh();
            }

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

                //销毁已经创建的单例Bean, 以避免资源占用.
                destroyBeans();

                //取消refresh操作, 重置active标志. 
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }

            finally {
                //重置Spring的核心缓存
                resetCommonCaches();
            }
        }
    }

2.3 Resources定位

refresh方法中obtainFreshBeanFactory方法调用了refreshBeanFactory，该方法使用DefaultListableBeanFactory去定位resources资源

protected final void refreshBeanFactory() throws BeansException {
        if (hasBeanFactory()) {
            destroyBeans();
            closeBeanFactory();
        }
        try {//创建并设置DefaultListableBeanFactory同时调用loadBeanDefinitions载入loadBeanDefinition
            DefaultListableBeanFactory beanFactory = createBeanFactory();
            beanFactory.setSerializationId(getId());
            customizeBeanFactory(beanFactory);
            loadBeanDefinitions(beanFactory);//核心方法
            synchronized (this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        }
        catch (IOException ex) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
        }
    }

loadBeanDefinitions其具体实现在AbstractXmlApplicationContext中，定义了一个Reader作为入参执行载入过程：

protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        // 为给定的bean工厂创建一个reader
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

        // Configure the bean definition reader with this context's
        // resource loading environment.
        beanDefinitionReader.setEnvironment(this.getEnvironment());
        beanDefinitionReader.setResourceLoader(this);
        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

        // Allow a subclass to provide custom initialization of the reader,
        // then proceed with actually loading the bean definitions.
        initBeanDefinitionReader(beanDefinitionReader);
        loadBeanDefinitions(beanDefinitionReader);//核心方法
    }

loadBeanDefinitions方法如下：

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
        Resource[] configResources = getConfigResources();
        if (configResources != null) {
            reader.loadBeanDefinitions(configResources);
        }
        String[] configLocations = getConfigLocations();
        if (configLocations != null) {
            reader.loadBeanDefinitions(configLocations);
        }
    }

getConfigResources采用模板方法设计模式，具体的实现由子类完成，实际上这里getConfigResources调用的就是子类ClassPathXmlApplicationContext的getConfigResources方法。ClassPathXmlApplicationContext继承了DefaultResourceLoader，具备了Resource加载资源的功能。至此完成了Resource定位！

2.4 BeanDefinition载入

这里支持2种模式：1.模板匹配多资源，生成Resource[]。2.载入单个资源url绝对地址，生成一个Resource

public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
        ResourceLoader resourceLoader = getResourceLoader();//获取ResourceLoader资源加载器
        if (resourceLoader == null) {
            throw new BeanDefinitionStoreException(
                    "Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
        }
        // 1.匹配模板解析 ClassPathXmlApplicationContext是ResourcePatternResolver接口的实例
        if (resourceLoader instanceof ResourcePatternResolver) {
           
            try {//接口ResourcePatternResolver
                Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
                int loadCount = loadBeanDefinitions(resources);
                if (actualResources != null) {
                    for (Resource resource : resources) {
                        actualResources.add(resource);
                    }
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
                }
                return loadCount;
            }
            catch (IOException ex) {
                throw new BeanDefinitionStoreException(
                        "Could not resolve bean definition resource pattern [" + location + "]", ex);
            }
        }
        else {
            // 2.载入单个资源url绝对地址
            Resource resource = resourceLoader.getResource(location);
            int loadCount = loadBeanDefinitions(resource);
            if (actualResources != null) {
                actualResources.add(resource);
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
            }
            return loadCount;
        }
    }

loadBeanDefinitions最终调用XmlBeanDefinitionReader.doLoadBeanDefinitions(),如下：

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {
        try {// 取得xml文件的Document,解析过程是由DocumentLoader完成，默认为DefaultDocumentLoader
            Document doc = doLoadDocument(inputSource, resource);
            return registerBeanDefinitions(doc, resource);// 启动对BeanDefinition的详细解析过程，这个解析会使用到spring的BEAN配置规则
        }
        catch (BeanDefinitionStoreException ex) {
            throw ex;
        }
        catch (SAXParseException ex) {
            throw new XmlBeanDefinitionStoreException(resource.getDescription(),
                    "Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
        }
        catch (SAXException ex) {
            throw new XmlBeanDefinitionStoreException(resource.getDescription(),
                    "XML document from " + resource + " is invalid", ex);
        }
        catch (ParserConfigurationException ex) {
            throw new BeanDefinitionStoreException(resource.getDescription(),
                    "Parser configuration exception parsing XML from " + resource, ex);
        }
        catch (IOException ex) {
            throw new BeanDefinitionStoreException(resource.getDescription(),
                    "IOException parsing XML document from " + resource, ex);
        }
        catch (Throwable ex) {
            throw new BeanDefinitionStoreException(resource.getDescription(),
                    "Unexpected exception parsing XML document from " + resource, ex);
        }
    }

registerBeanDefinitions是按照spring的bean配置规则解析，源码如下：

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        int countBefore = getRegistry().getBeanDefinitionCount();
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));// 核心方法
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }

至此就完成了BeanDefinition的载入，BeanDefinition的载入分为两个部分，

1.调用xml解析器得到的document对象，但是这个对象并没有按照spring的bean规则进行解析。

2.DefaultBeanDefinitionDocumentReader的registerBeanDefinitions按照Spring的Bean规则进行解析。

2.5 BeanDefinition解析和注册

registerBeanDefinitions方法调用了doRegisterBeanDefinitions

protected void doRegisterBeanDefinitions(Element root) {
        // Any nested <beans> elements will cause recursion in this method. In
        // order to propagate and preserve <beans> default-* attributes correctly,
        // keep track of the current (parent) delegate, which may be null. Create
        // the new (child) delegate with a reference to the parent for fallback purposes,
        // then ultimately reset this.delegate back to its original (parent) reference.
        // this behavior emulates a stack of delegates without actually necessitating one.
        BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = createDelegate(getReaderContext(), root, parent);

        if (this.delegate.isDefaultNamespace(root)) {
            String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
            if (StringUtils.hasText(profileSpec)) {
                String[] specifiedProfiles = StringUtils.tokenizeToStringArray(
                        profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
                if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
                    if (logger.isInfoEnabled()) {
                        logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec +
                                "] not matching: " + getReaderContext().getResource());
                    }
                    return;
                }
            }
        }

        preProcessXml(root);
        parseBeanDefinitions(root, this.delegate);// 从Document的根元素开始进行Bean定义的Document对象
        postProcessXml(root);

        this.delegate = parent;
    }

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        if (delegate.isDefaultNamespace(root)) {
            NodeList nl = root.getChildNodes();
            for (int i = 0; i < nl.getLength(); i++) {
                Node node = nl.item(i);
                if (node instanceof Element) {
                    Element ele = (Element) node;
                    if (delegate.isDefaultNamespace(ele)) {
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

    private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
            importBeanDefinitionResource(ele);
        }
        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
            processAliasRegistration(ele);
        }
        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
            processBeanDefinition(ele, delegate);
        }
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
    }

processBeanDefinition就是对bean标签的解析和注册

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);// 1.解析
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);//代理去装饰：典型的装饰器模式
            try {
                // 2.向IOC容器注册Bean定义+bean工厂
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +
                        bdHolder.getBeanName() + "'", ele, ex);
            }
            // 3.触发注册事件： spring只提供了EmptyReaderEventListener空实现，如果需要你可以自定义
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }

解析：parseBeanDefinitionElement方法就是具体的解析入口。解析elemnent->BeanDefinitionHolder,追踪parseBeanDefinitionElement:

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
        String id = ele.getAttribute(ID_ATTRIBUTE);// 获取id
        String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);// 获取name

        List<String> aliases = new ArrayList<String>();// 获取别名
        if (StringUtils.hasLength(nameAttr)) {
            String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
            aliases.addAll(Arrays.asList(nameArr));
        }

        String beanName = id;
        if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
            beanName = aliases.remove(0);
            if (logger.isDebugEnabled()) {
                logger.debug("No XML 'id' specified - using '" + beanName +
                        "' as bean name and " + aliases + " as aliases");
            }
        }

        if (containingBean == null) {
            checkNameUniqueness(beanName, aliases, ele);
        }

        AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
        if (beanDefinition != null) {
            if (!StringUtils.hasText(beanName)) {
                try {
                    if (containingBean != null) {
                        beanName = BeanDefinitionReaderUtils.generateBeanName(
                                beanDefinition, this.readerContext.getRegistry(), true);
                    }
                    else {
                        beanName = this.readerContext.generateBeanName(beanDefinition);
                        // Register an alias for the plain bean class name, if still possible,
                        // if the generator returned the class name plus a suffix.
                        // This is expected for Spring 1.2/2.0 backwards compatibility.
                        String beanClassName = beanDefinition.getBeanClassName();
                        if (beanClassName != null &&
                                beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
                                !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                            aliases.add(beanClassName);
                        }
                    }
                    if (logger.isDebugEnabled()) {
                        logger.debug("Neither XML 'id' nor 'name' specified - " +
                                "using generated bean name [" + beanName + "]");
                    }
                }
                catch (Exception ex) {
                    error(ex.getMessage(), ele);
                    return null;
                }
            }
            String[] aliasesArray = StringUtils.toStringArray(aliases);
            return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        }

        return null;
    }

好吧，parseBeanDefinitionElement才是核心方法，追踪：

public AbstractBeanDefinition parseBeanDefinitionElement(
            Element ele, String beanName, BeanDefinition containingBean) {

        this.parseState.push(new BeanEntry(beanName));

        String className = null;
        if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
            className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
        }

        try {
            String parent = null;
            if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
                parent = ele.getAttribute(PARENT_ATTRIBUTE);
            }// 这里生成需要的BeanDefinition对象，为Bean定义信息的载入做准备
            AbstractBeanDefinition bd = createBeanDefinition(className, parent);
            // 1.解析<bean>元素属性
            parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));//2.解析description
            //对各种BEAN元素信息进行解析
            parseMetaElements(ele, bd);// 3.解析<meta>子元素
            parseLookupOverrideSubElements(ele, bd.getMethodOverrides());//4.解析<lookup-method>子元素
            parseReplacedMethodSubElements(ele, bd.getMethodOverrides());//5.解析<replaced-method>子元素

            parseConstructorArgElements(ele, bd);//6.解析<constructor-arg>
            parsePropertyElements(ele, bd);//7.解析<property>
            parseQualifierElements(ele, bd);//8.解析<qualifier>

            bd.setResource(this.readerContext.getResource());
            bd.setSource(extractSource(ele));

            return bd;
        }
        catch (ClassNotFoundException ex) {
            error("Bean class [" + className + "] not found", ele, ex);
        }
        catch (NoClassDefFoundError err) {
            error("Class that bean class [" + className + "] depends on not found", ele, err);
        }
        catch (Throwable ex) {
            error("Unexpected failure during bean definition parsing", ele, ex);
        }
        finally {
            this.parseState.pop();
        }

        return null;
    }

经过这样逐层的分析，我们在xml文件中定义的BeanDefinition就被整个载入到IOC容器中，并在容器中建立了数据映射。这些数据结构可以以AbstractBeanDefinition为入口让IOC容器执行索引，查询和操作。

注册：registerBeanDefinition方法就是具体的注册入口。追踪registerBeanDefinition:

public static void registerBeanDefinition(
            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
            throws BeanDefinitionStoreException {

        // Register bean definition under primary name.
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());//向IoC容器注册BeanDefinition

        // 如果解析的BeanDefinition有别名, 向容器为其注册别名. 
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
    }

registerBeanDefinition具体实现类：DefaultListableBeanFactory.registerBeanDefinition方法

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");

        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }

        BeanDefinition oldBeanDefinition;

        oldBeanDefinition = this.beanDefinitionMap.get(beanName);
        if (oldBeanDefinition != null) {
            if (!isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
                        "': There is already [" + oldBeanDefinition + "] bound.");
            }
            else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
                            "' with a framework-generated bean definition: replacing [" +
                            oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
            else if (!beanDefinition.equals(oldBeanDefinition)) {
                if (this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean '" + beanName +
                            "' with a different definition: replacing [" + oldBeanDefinition +
                            "] with [" + beanDefinition + "]");
                }
            }
            else {
                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Overriding bean definition for bean '" + beanName +
                            "' with an equivalent definition: replacing [" + oldBeanDefinition +
                            "] with [" + beanDefinition + "]");
                }
            }
            this.beanDefinitionMap.put(beanName, beanDefinition);
        }
        else {
            if (hasBeanCreationStarted()) {
                // Cannot modify startup-time collection elements anymore (for stable iteration)
                synchronized (this.beanDefinitionMap) {
                    this.beanDefinitionMap.put(beanName, beanDefinition);
                    List<String> updatedDefinitions = new ArrayList<String>(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    if (this.manualSingletonNames.contains(beanName)) {
                        Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames);
                        updatedSingletons.remove(beanName);
                        this.manualSingletonNames = updatedSingletons;
                    }
                }
            }
            else {
                // Still in startup registration phase
                this.beanDefinitionMap.put(beanName, beanDefinition);
                this.beanDefinitionNames.add(beanName);
                this.manualSingletonNames.remove(beanName);
            }
            this.frozenBeanDefinitionNames = null;
        }

        if (oldBeanDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
    }

完成了BeanDefinition的注册，就完成了IOC容器的初始化过程。容器的作用就是对这些信息进行处理和维护，这些信息就是容器建立依赖反转的基础。

三、总结

本文先介绍ApplicationContext接口设计，再从其一个最常见实现类ClassPathXmlApplicationContext写了一个小例子，作为源码追踪的入口。

追踪了主要包括Resourse定位、BeanDefinition的载入、解析和注册3个模块。至此，容器初始化（Bean已生成）已完成，下一章我们看依赖注入的源码。