Spring-IOC容器容器

摘要：使用别名时，容器首先将别名元素所定义的别名注册到容器中。调用的方法向容器注册解析的通过对对象的解析和封装返回一个通过这个来注册对象当调用向容器注册解析的时，真正完成注册功能的是。

文章参考来自：https://www.cnblogs.com/ITtan...
文章代码来自 spring-boot 1.4.1 Release版本

Spring IoC容器对Bean定义资源的载入是从refresh()函数开始的，refresh()是一个模板方法，refresh()方法的作用是：在创建IoC容器前，如果已经有容器存在，则需要把已有的容器销毁和关闭，以保证在refresh之后使用的是新建立起来的IoC容器。refresh的作用类似于对IoC容器的重启，在新建立好的容器中对容器进行初始化，对Bean定义资源进行载入

public void refresh() throws BeansException, IllegalStateException {
       Object var1 = this.startupShutdownMonitor;
       synchronized(this.startupShutdownMonitor) {
           //调用容器准备刷新的方法，获取容器的当时时间，同时给容器设置同步标识
           this.prepareRefresh();
           //告诉子类启动refreshBeanFactory()方法，Bean定义资源文件的载入从  
           //子类的refreshBeanFactory()方法启动 
           //这个bean的载入过程 包括对xml的解析和加载为BeanDefinitions 都是从this.obtainFreshBeanFactory()这里进入
           ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
           /*这之后的代码都是注册容器的信息源和生命周期事件*/
           //为BeanFactory配置容器特性，例如类加载器、事件处理器等
           this.prepareBeanFactory(beanFactory);

           try {
               //为容器的某些子类指定特殊的BeanPost事件处理器
               this.postProcessBeanFactory(beanFactory);
               //调用所有注册的BeanFactoryPostProcessor的Bean
               this.invokeBeanFactoryPostProcessors(beanFactory);
               //为BeanFactory注册BeanPost事件处理器.  
               //BeanPostProcessor是Bean后置处理器，用于监听容器触发的事件 
               this.registerBeanPostProcessors(beanFactory);
               //初始化信息源，和国际化相关.
               this.initMessageSource();
               //初始化容器事件传播器.
               this.initApplicationEventMulticaster();
               //调用子类的某些特殊Bean初始化方法
               this.onRefresh();
               //为事件传播器注册事件监听器. 
               this.registerListeners();
               //初始化所有剩余的单态Bean.
               this.finishBeanFactoryInitialization(beanFactory);
               //初始化容器的生命周期事件处理器，并发布容器的生命周期事件
               this.finishRefresh();
           } catch (BeansException var9) {
               if (this.logger.isWarnEnabled()) {
                   this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
               }
               //销毁以创建的单态Bean
               this.destroyBeans();
               //取消refresh操作，重置容器的同步标识.
               this.cancelRefresh(var9);
               throw var9;
           } finally {
               this.resetCommonCaches();
           }

       }
   }

AbstractRefreshableApplicationContext 类：
AbstractRefreshableApplicationContext中只定义了抽象的loadBeanDefinitions方法，容器真正调用的是其子类AbstractXmlApplicationContext对该方法的实现

protected final void refreshBeanFactory() throws BeansException {
        //如果已经创建了BeanFactory，则销毁并关闭BeanFactory
        if (this.hasBeanFactory()) {
            this.destroyBeans();
            this.closeBeanFactory();
        }

        try {
             //创建了一个IOC容器
            DefaultListableBeanFactory beanFactory = this.createBeanFactory();
            beanFactory.setSerializationId(this.getId());
            /对IoC容器进行定制化，如设置启动参数，开启注解的自动装配等
            this.customizeBeanFactory(beanFactory);
            //调用载入Bean定义的方法，主要这里又使用了一个委派模式，在当前类中只定义了抽象的loadBeanDefinitions方法，具体的实现调用子类容器
            this.loadBeanDefinitions(beanFactory);
            Object var2 = this.beanFactoryMonitor;
            synchronized(this.beanFactoryMonitor) {
                this.beanFactory = beanFactory;
            }
        } catch (IOException var5) {
            throw new ApplicationContextException("I/O error parsing bean definition source for " + this.getDisplayName(), var5);
        }
    }

AbstractXmlApplicationContext 类：

 protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        //创建XmlBeanDefinitionReader，即创建Bean读取器，并通过回调设置到容器中去，容器使用该读取器读取Bean定义资源  
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
        beanDefinitionReader.setEnvironment(this.getEnvironment());
         //为Bean读取器设置Spring资源加载器，AbstractXmlApplicationContext的  
        //祖先父类AbstractApplicationContext继承DefaultResourceLoader，因此，容器本身也是一个资源加载器
        beanDefinitionReader.setResourceLoader(this);
        //为Bean读取器设置SAX xml解析器 
        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
        //当Bean读取器读取Bean定义的Xml资源文件时，启用Xml的校验机制  
        this.initBeanDefinitionReader(beanDefinitionReader);
        //Bean读取器真正实现加载的方法
        this.loadBeanDefinitions(beanDefinitionReader);
    }
    
    protected void initBeanDefinitionReader(XmlBeanDefinitionReader reader) {
        reader.setValidating(this.validating);
    }

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

        String[] configLocations = this.getConfigLocations();
        if (configLocations != null) {
            reader.loadBeanDefinitions(configLocations);
        }

    }

    @Nullable
    protected Resource[] getConfigResources() {
        return null;
    }

在其抽象父类AbstractBeanDefinitionReader中定义了载入过程

 public int loadBeanDefinitions(String location, @Nullable Set actualResources) throws BeanDefinitionStoreException {
        //获取resourceLoader
        ResourceLoader resourceLoader = this.getResourceLoader();
        if (resourceLoader == null) {
            throw new BeanDefinitionStoreException("Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
        } else {
            int loadCount;
            if (!(resourceLoader instanceof ResourcePatternResolver)) {
                //将指定位置的Bean定义资源文件解析为Spring IoC容器封装的资源  
                //加载多个指定位置的Bean定义资源文件 完成具体的资源定位的工作               
                Resource resource = resourceLoader.getResource(location);
                //加载资源 开始我们的第二步操作 转换为BeanDefinition对象
                loadCount = this.loadBeanDefinitions((Resource)resource);
                if (actualResources != null) {
                    actualResources.add(resource);
                }

                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
                }

                return loadCount;
            } else {
                try {
                   //将指定位置的Bean定义资源文件解析为Spring IoC容器封装的资源  
                   //加载单个指定位置的Bean定义资源文件  
                    Resource[] resources = ((ResourcePatternResolver)resourceLoader).getResources(location);
                    //加载资源 开始我们的第二步操作 转换为BeanDefinition对象
                    loadCount = this.loadBeanDefinitions(resources);
                    if (actualResources != null) {
                        Resource[] var6 = resources;
                        int var7 = resources.length;

                        for(int var8 = 0; var8 < var7; ++var8) {
                            Resource resource = var6[var8];
                            actualResources.add(resource);
                        }
                    }

                    if (this.logger.isDebugEnabled()) {
                        this.logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
                    }

                    return loadCount;
                } catch (IOException var10) {
                    throw new BeanDefinitionStoreException("Could not resolve bean definition resource pattern [" + location + "]", var10);
                }
            }
        }
    }

具体加载资源的方法
首先，调用资源加载器的获取资源方法resourceLoader.getResource(location)，获取到要加载的资源。
其次，真正执行加载功能是其子类XmlBeanDefinitionReader的loadBeanDefinitions方法。
资源定位到这里就结束 最终返回的是一个Resource的对象来进行BeanDefinition的载入。在定位完成后,为BeanDefinition的载入创客I/O条件，
但是具体的载入还没有开始载入。

public Resource getResource(String location) {
        Assert.notNull(location, "Location must not be null");
        Iterator var2 = this.protocolResolvers.iterator();

        Resource resource;
        do {
            if (!var2.hasNext()) {
               //处理/开头的定位
                if (location.startsWith("/")) {
                    return this.getResourceByPath(location);
                }
                //带有classpath标识的Resource
                if (location.startsWith("classpath:")) {
                    return new ClassPathResource(location.substring("classpath:".length()), this.getClassLoader());
                }

                try {
                //处理URL标识的Resource定位
                    URL url = new URL(location);
                    return (Resource)(ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
                } catch (MalformedURLException var5) {
                    //如果不存classpath、Url、/标志的 就教给他处理
                    return this.getResourceByPath(location);
                }
            }

            ProtocolResolver protocolResolver = (ProtocolResolver)var2.next();
            resource = protocolResolver.resolve(location, this);
        } while(resource == null);

        return resource;
    }

protected Resource getResourceByPath(String path) {    
   if (path != null && path.startsWith("/")) {    
        path = path.substring(1);    
    }  
    //这里使用文件系统资源对象来定义bean 文件
    return new FileSystemResource(path);  
}

BeanDefinition的载入分成两部分,首先通过XML的解析器得到document对象，
但这些document对象没有按照spring的Bean规则进行解析。在完成XML解析后，才是按照Spring的Bean规则进行解析，这个解析的过程是在documentReader实现。

 public int loadBeanDefinitions(String location, @Nullable Set actualResources) throws BeanDefinitionStoreException {
        //获取resourceLoader
        ResourceLoader resourceLoader = this.getResourceLoader();
        if (resourceLoader == null) {
            throw new BeanDefinitionStoreException("Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
        } else {
            int loadCount;
            if (!(resourceLoader instanceof ResourcePatternResolver)) {
                //将指定位置的Bean定义资源文件解析为Spring IoC容器封装的资源  
                //加载多个指定位置的Bean定义资源文件 完成具体的资源定位的工作               
                Resource resource = resourceLoader.getResource(location);
 
                //加载资源 开始我们的第二步操作 转换为BeanDefinition对象
                loadCount = this.loadBeanDefinitions((Resource)resource);
                if (actualResources != null) {
                    actualResources.add(resource);
                }

                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
                }

                return loadCount;
            } else {
                try {
                   //将指定位置的Bean定义资源文件解析为Spring IoC容器封装的资源  
                   //加载单个指定位置的Bean定义资源文件  
                    Resource[] resources = ((ResourcePatternResolver)resourceLoader).getResources(location);
                    //加载资源 开始我们的第二步操作 转换为BeanDefinition对象
                    loadCount = this.loadBeanDefinitions(resources);
                    if (actualResources != null) {
                        Resource[] var6 = resources;
                        int var7 = resources.length;

                        for(int var8 = 0; var8 < var7; ++var8) {
                            Resource resource = var6[var8];
                            actualResources.add(resource);
                        }
                    }

                    if (this.logger.isDebugEnabled()) {
                        this.logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
                    }

                    return loadCount;
                } catch (IOException var10) {
                    throw new BeanDefinitionStoreException("Could not resolve bean definition resource pattern [" + location + "]", var10);
                }
            }
        }
    }

xml文件转换为document对象 再解析BeanDefinition
这里是载入XML形式Bean定义资源文件方法

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
        Assert.notNull(encodedResource, "EncodedResource must not be null");
        if(this.logger.isInfoEnabled()) {
            this.logger.info("Loading XML bean definitions from " + encodedResource.getResource());
        }

        Set currentResources = (Set)this.resourcesCurrentlyBeingLoaded.get();
        if(currentResources == null) {
            currentResources = new HashSet(4);
            this.resourcesCurrentlyBeingLoaded.set(currentResources);
        }

        if(!((Set)currentResources).add(encodedResource)) {
            throw new BeanDefinitionStoreException("Detected cyclic loading of " + encodedResource + " - check your import definitions!");
        } else {
            int var5;
            try {
                //将资源文件转为InputStream的IO流
                InputStream inputStream = encodedResource.getResource().getInputStream();

                try {
                    //从InputStream中得到XML的解析源
                    InputSource inputSource = new InputSource(inputStream);
                    if(encodedResource.getEncoding() != null) {
                        inputSource.setEncoding(encodedResource.getEncoding());
                    }
                     //这里是具体的读取过程
                    var5 = this.doLoadBeanDefinitions(inputSource, encodedResource.getResource());
                } finally {
                    //IO流的关闭
                    inputStream.close();
                }
            } catch (IOException var15) {
                throw new BeanDefinitionStoreException("IOException parsing XML document from " + encodedResource.getResource(), var15);
            } finally {
                ((Set)currentResources).remove(encodedResource);
                if(((Set)currentResources).isEmpty()) {
                    this.resourcesCurrentlyBeingLoaded.remove();
                }

            }

            return var5;
        }
    }

    protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException {
        try {
            //@1将XML文件转换为DOM对象，解析过程由documentLoader实现
            Document doc = this.doLoadDocument(inputSource, resource);
            //@2这里是启动对Bean定义解析的详细过程，该解析过程会用到Spring的Bean配置规则
            return this.registerBeanDefinitions(doc, resource);
        } catch (BeanDefinitionStoreException var4) {
            throw var4;
        } catch (SAXParseException var5) {
            throw new XmlBeanDefinitionStoreException(resource.getDescription(), "Line " + var5.getLineNumber() + " in XML document from " + resource + " is invalid", var5);
        } catch (SAXException var6) {
            throw new XmlBeanDefinitionStoreException(resource.getDescription(), "XML document from " + resource + " is invalid", var6);
        } catch (ParserConfigurationException var7) {
            throw new BeanDefinitionStoreException(resource.getDescription(), "Parser configuration exception parsing XML from " + resource, var7);
        } catch (IOException var8) {
            throw new BeanDefinitionStoreException(resource.getDescription(), "IOException parsing XML document from " + resource, var8);
        } catch (Throwable var9) {
            throw new BeanDefinitionStoreException(resource.getDescription(), "Unexpected exception parsing XML document from " + resource, var9);
        }
    }

@1

//使用标准的JAXP将载入的Bean定义资源转换成document对象
 public Document loadDocument(InputSource inputSource, EntityResolver entityResolver, ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {
        //创建文件解析器工厂 
        DocumentBuilderFactory factory = this.createDocumentBuilderFactory(validationMode, namespaceAware);
        if(logger.isDebugEnabled()) {
            logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
        }
        //创建文档解析器  
        DocumentBuilder builder = this.createDocumentBuilder(factory, entityResolver, errorHandler);
        //解析Spring的Bean定义资源
        return builder.parse(inputSource);
    }

    protected DocumentBuilderFactory createDocumentBuilderFactory(int validationMode, boolean namespaceAware) throws ParserConfigurationException {
     //创建文档解析工厂
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(namespaceAware);
        if(validationMode != 0) {
           //设置解析XML的校验 
            factory.setValidating(true);
            if(validationMode == 3) {
                factory.setNamespaceAware(true);

                try {
                    factory.setAttribute("http://java.sun.com/xml/jaxp/properties/schemaLanguage", "http://www.w3.org/2001/XMLSchema");
                } catch (IllegalArgumentException var6) {
                    ParserConfigurationException pcex = new ParserConfigurationException("Unable to validate using XSD: Your JAXP provider [" + factory + "] does not support XML Schema. Are you running on Java 1.4 with Apache Crimson? Upgrade to Apache Xerces (or Java 1.5) for full XSD support.");
                    pcex.initCause(var6);
                    throw pcex;
                }
            }
        }

        return factory;
    } 

Spring IoC容器根据定位的Bean定义资源文件，将其加载读入并转换成为Document对象过程完成。

下面是 Spring IoC容器将载入的Bean定义资源文件转换为Document对象之后，是如何将其解析为Spring IoC管理的Bean对象并将其注册到容器中的
@2

 //按照Spring的Bean语义要求将Bean定义资源解析并转换为容器内部数据结构
 public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        /得到BeanDefinitionDocumentReader来对xml格式的BeanDefinition解析 
        BeanDefinitionDocumentReader documentReader = this.createBeanDefinitionDocumentReader();
        //获得容器中注册的Bean数量
        int countBefore = this.getRegistry().getBeanDefinitionCount();
        //解析过程入口，这里使用了委派模式，BeanDefinitionDocumentReader只是个接口
        //具体的解析实现过程有实现类DefaultBeanDefinitionDocumentReader完成
        //@1
        documentReader.registerBeanDefinitions(doc, this.createReaderContext(resource));
        /统计解析的Bean数量 
        return this.getRegistry().getBeanDefinitionCount() - countBefore;
    }
    //创建BeanDefinitionDocumentReader对象，解析Document对象
    protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
        return (BeanDefinitionDocumentReader)BeanDefinitionDocumentReader.class.cast(BeanUtils.instantiateClass(this.documentReaderClass));
    }
    

DefaultBeanDefinitionDocumentReader 解析document对象按照spring Bean的定义规则转换为BeanDefinition
@1

 public class DefaultBeanDefinitionDocumentReader implements BeanDefinitionDocumentReader {
    public static final String BEAN_ELEMENT = "bean";
    public static final String NESTED_BEANS_ELEMENT = "beans";
    public static final String ALIAS_ELEMENT = "alias";
    public static final String NAME_ATTRIBUTE = "name";
    public static final String ALIAS_ATTRIBUTE = "alias";
    public static final String IMPORT_ELEMENT = "import";
    public static final String RESOURCE_ATTRIBUTE = "resource";
    public static final String PROFILE_ATTRIBUTE = "profile";
    protected final Log logger = LogFactory.getLog(this.getClass());
    private XmlReaderContext readerContext;
    private BeanDefinitionParserDelegate delegate;

    public DefaultBeanDefinitionDocumentReader() {
    }
    //根据Spring DTD对Bean的定义规则解析Bean定义Document对象 
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        //获得XML描述符 
        this.readerContext = readerContext;
        this.logger.debug("Loading bean definitions");
        //获得Document的根元素 
        Element root = doc.getDocumentElement();
        this.doRegisterBeanDefinitions(root);
    }

    protected final XmlReaderContext getReaderContext() {
        return this.readerContext;
    }

    protected Object extractSource(Element ele) {
        return this.getReaderContext().extractSource(ele);
    }
    //具体的解析过程由BeanDefinitionParserDelegate实现，  
    //BeanDefinitionParserDelegate中定义了Spring Bean定义XML文件的各种元素
    protected void doRegisterBeanDefinitions(Element root) {
        BeanDefinitionParserDelegate parent = this.delegate;
        this.delegate = this.createDelegate(this.getReaderContext(), root, parent);
        if(this.delegate.isDefaultNamespace(root)) {
            String profileSpec = root.getAttribute("profile");
            if(StringUtils.hasText(profileSpec)) {
                String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, ",; ");
                if(!this.getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) {
                    if(this.logger.isInfoEnabled()) {
                        this.logger.info("Skipped XML bean definition file due to specified profiles [" + profileSpec + "] not matching: " + this.getReaderContext().getResource());
                    }

                    return;
                }
            }
        }
        //在解析Bean定义之前，进行自定义的解析，增强解析过程的可扩展性
        this.preProcessXml(root);
        //从Document的根元素开始进行Bean定义的Document对象
        this.parseBeanDefinitions(root, this.delegate);
        //在解析Bean定义之后，进行自定义的解析，增加解析过程的可扩展性
        this.postProcessXml(root);
        this.delegate = parent;
    }
    //创建BeanDefinitionParserDelegate，用于完成真正的解析过程
    protected BeanDefinitionParserDelegate createDelegate(XmlReaderContext readerContext, Element root, BeanDefinitionParserDelegate parentDelegate) {
        BeanDefinitionParserDelegate delegate = new BeanDefinitionParserDelegate(readerContext);
        //BeanDefinitionParserDelegate初始化Document根元素
        delegate.initDefaults(root, parentDelegate);
        return delegate;
    }
    //使用Spring的Bean规则从Document的根元素开始进行Bean定义的Document对象
    protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
         //Bean定义的Document对象使用了Spring默认的XML命名空间
        if(delegate.isDefaultNamespace(root)) {
           //获取Bean定义的Document对象根元素的所有子节点
            NodeList nl = root.getChildNodes();

            for(int i = 0; i < nl.getLength(); ++i) {
                Node node = nl.item(i);
                //获得Document节点是XML元素节点
                if(node instanceof Element) {
                    Element ele = (Element)node;
                    //Bean定义的Document的元素节点使用的是Spring默认的XML命名空间
                    if(delegate.isDefaultNamespace(ele)) {
                        //使用Spring的Bean规则解析元素节点
                        this.parseDefaultElement(ele, delegate);
                    } else {
                       //没有使用Spring默认的XML命名空间，则使用用户自定义的解//析规则解析元素节点
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        } else {
            //Document的根节点没有使用Spring默认的命名空间，则使用用户自定义的  
           //解析规则解析Document根节点
            delegate.parseCustomElement(root);
        }

    }

    private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        //如果元素节点是导入元素，进行导入解析  
        if(delegate.nodeNameEquals(ele, "import")) {
            this.importBeanDefinitionResource(ele);
            
        } else if(delegate.nodeNameEquals(ele, "alias")) {
        //如果元素节点是别名元素，进行别名解析 
            this.processAliasRegistration(ele);
        } else if(delegate.nodeNameEquals(ele, "bean")) {
        //元素节点既不是导入元素，也不是别名元素，即普通的元素，  
        //按照Spring的Bean规则解析元素  
            this.processBeanDefinition(ele, delegate);
        } else if(delegate.nodeNameEquals(ele, "beans")) {
         //如果元素节点是元素注册为BeanDefintion
            this.doRegisterBeanDefinitions(ele);
        }

    }
    //解析导入元素，从给定的导入路径加载Bean定义资源到Spring IoC容器中
    protected void importBeanDefinitionResource(Element ele) {
        /获取给定的导入元素的location属性 
        String location = ele.getAttribute("resource");
        if(!StringUtils.hasText(location)) {
            this.getReaderContext().error("Resource location must not be empty", ele);
        } else {
            //获取location的值 
            location = this.getReaderContext().getEnvironment().resolveRequiredPlaceholders(location);
            Set actualResources = new LinkedHashSet(4);
            //标识给定的导入元素的location是否是绝对路径
            boolean absoluteLocation = false;

            try {
                absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute();
            } catch (URISyntaxException var11) {
                ;
            }

            int importCount;
            if(absoluteLocation) {
                try {
                    //使用资源读入器加载给定路径的Bean定义资源
                    importCount = this.getReaderContext().getReader().loadBeanDefinitions(location, actualResources);
                    if(this.logger.isDebugEnabled()) {
                        this.logger.debug("Imported " + importCount + " bean definitions from URL location [" + location + "]");
                    }
                } catch (BeanDefinitionStoreException var10) {
                    this.getReaderContext().error("Failed to import bean definitions from URL location [" + location + "]", ele, var10);
                }
            } else {
            //给定的导入元素的location是相对路径  
                try {
                    Resource relativeResource = this.getReaderContext().getResource().createRelative(location);
                    if(relativeResource.exists()) {
                         //使用资源读入器加载Bean定义资源 
                        importCount = this.getReaderContext().getReader().loadBeanDefinitions(relativeResource);
                        actualResources.add(relativeResource);
                    } else {
                        String baseLocation = this.getReaderContext().getResource().getURL().toString();
                        importCount = this.getReaderContext().getReader().loadBeanDefinitions(StringUtils.applyRelativePath(baseLocation, location), actualResources);
                    }

                    if(this.logger.isDebugEnabled()) {
                        this.logger.debug("Imported " + importCount + " bean definitions from relative location [" + location + "]");
                    }
                } catch (IOException var8) {
                    this.getReaderContext().error("Failed to resolve current resource location", ele, var8);
                } catch (BeanDefinitionStoreException var9) {
                    this.getReaderContext().error("Failed to import bean definitions from relative location [" + location + "]", ele, var9);
                }
            }
            //在解析完元素之后，发送容器导入其他资源处理完成事件
            Resource[] actResArray = (Resource[])actualResources.toArray(new Resource[actualResources.size()]);
            this.getReaderContext().fireImportProcessed(location, actResArray, this.extractSource(ele));
        }
    }
   //解析别名元素，为Bean向Spring IoC容器注册别名  
    protected void processAliasRegistration(Element ele) {
        //获取别名元素中name的属性值
        String name = ele.getAttribute("name");
        //获取别名元素中alias的属性值  
        String alias = ele.getAttribute("alias");
        boolean valid = true;
        if(!StringUtils.hasText(name)) {
            this.getReaderContext().error("Name must not be empty", ele);
            valid = false;
        }

        if(!StringUtils.hasText(alias)) {
            this.getReaderContext().error("Alias must not be empty", ele);
            valid = false;
        }

        if(valid) {
            try {
                //向容器的资源读入器注册别名
                this.getReaderContext().getRegistry().registerAlias(name, alias);
            } catch (Exception var6) {
                this.getReaderContext().error("Failed to register alias "" + alias + "" for bean with name "" + name + """, ele, var6);
            }
            //在解析完元素之后，发送容器别名处理完成事件
            this.getReaderContext().fireAliasRegistered(name, alias, this.extractSource(ele));
        }

    } 
    //解析Bean定义资源Document对象的普通元素
    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        // BeanDefinitionHolder是对BeanDefinition的封装，即Bean定义的封装类  
       //对Document对象中元素的解析由BeanDefinitionParserDelegate实现  BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); 
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if(bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);

            try {
                //向Spring IoC容器注册解析得到的Bean定义，这是Bean定义向IoC容器注册的入口
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
            } catch (BeanDefinitionStoreException var5) {
                this.getReaderContext().error("Failed to register bean definition with name "" + bdHolder.getBeanName() + """, ele, var5);
            }
            //在完成向Spring IoC容器注册解析得到的Bean定义之后，发送注册事件
            this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }

    }

    protected void preProcessXml(Element root) {
    }

    protected void postProcessXml(Element root) {
    }
}

通过上述Spring IoC容器对载入的Bean定义Document解析可以看出，我们使用Spring时，在Spring配置文件中可以使用元素来导入IoC容器所需要的其他资源，Spring IoC容器在解析时会首先将指定导入的资源加载进容器中。使用别名时，Spring IoC容器首先将别名元素所定义的别名注册到容器中。
对于既不是元素，又不是元素的元素，即Spring配置文件中普通的元素的解析由BeanDefinitionParserDelegate类的parseBeanDefinitionElement方法来实现。

下面是针对对Bean元素的解析过程

    //解析Bean定义资源文件中的元素，这个方法中主要处理元素的id，name
    public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
        //获取id属性
        String id = ele.getAttribute("id");
        //获取name属性
        String nameAttr = ele.getAttribute("name");
        List aliases = new ArrayList();
        //将Bean元素的name属性全部放到alias属性里面
        if(StringUtils.hasLength(nameAttr)) {
            String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, ",; ");
            aliases.addAll(Arrays.asList(nameArr));
        }

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

        if(containingBean == null) {
            //检查bean元素的id和name是否是唯一的 
            this.checkNameUniqueness(beanName, aliases, ele);
        }
        //详细对元素中配置的Bean定义进行解析的地方
        AbstractBeanDefinition beanDefinition = this.parseBeanDefinitionElement(ele, beanName, containingBean);
        if(beanDefinition != null) {
            if(!StringUtils.hasText(beanName)) {
                try {
                    if(containingBean != null) {
                        //判断如果没有id和name属性时候是否包含子元素的
                        beanName = BeanDefinitionReaderUtils.generateBeanName(beanDefinition, this.readerContext.getRegistry(), true);
                    } else {
                        //如果元素中没有配置id、别名或者name，且包含了子//元素，为解析的Bean使用别名向IoC容器注册  
                        beanName = this.readerContext.generateBeanName(beanDefinition);
                        String beanClassName = beanDefinition.getBeanClassName();
                        if(beanClassName != null && beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() && !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                            aliases.add(beanClassName);
                        }
                    }

                    if(this.logger.isDebugEnabled()) {
                        this.logger.debug("Neither XML "id" nor "name" specified - using generated bean name [" + beanName + "]");
                    }
                } catch (Exception var9) {
                    this.error(var9.getMessage(), ele);
                    return null;
                }
            }

            String[] aliasesArray = StringUtils.toStringArray(aliases);
            return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        } else {
            return null;
        }
    }
    //详细解析bean元素的地方
    public AbstractBeanDefinition parseBeanDefinitionElement(Element ele, String beanName, BeanDefinition containingBean) {
        this.parseState.push(new BeanEntry(beanName));
        String className = null;
        //是否包含class属性
        if(ele.hasAttribute("class")) {
            //获取class属性值 不做实例化，bean的实例化是在第一次获取bean的时候完成，这里只获取class的值
            className = ele.getAttribute("class").trim();
        }

        try {
            String parent = null;
            //如果元素中配置了parent属性，则获取parent属性的值
            if(ele.hasAttribute("parent")) {
                parent = ele.getAttribute("parent");
            }
           //根据元素配置的class名称和parent属性值创建BeanDefinition  
            //为载入Bean定义信息做准备 
            AbstractBeanDefinition bd = this.createBeanDefinition(className, parent);
            //对当前的元素中配置的一些属性进行解析和设置，如配置的单态(singleton)属性等
            this.parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            //为元素解析的Bean设置description信息 bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, "description"));
            //对元素的meta(元信息)属性解析
            this.parseMetaElements(ele, bd);
            //对元素的lookup-method属性解析
            this.parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
            //对元素的replaced-method属性解析
            this.parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
            //解析元素的构造方法设置
            this.parseConstructorArgElements(ele, bd);
             //解析元素的设置
            this.parsePropertyElements(ele, bd);
             //解析元素的qualifier属性
            this.parseQualifierElements(ele, bd);
            bd.setResource(this.readerContext.getResource());
            bd.setSource(this.extractSource(ele));
            AbstractBeanDefinition var7 = bd;
            return var7;
        } catch (ClassNotFoundException var13) {
            this.error("Bean class [" + className + "] not found", ele, var13);
        } catch (NoClassDefFoundError var14) {
            this.error("Class that bean class [" + className + "] depends on not found", ele, var14);
        } catch (Throwable var15) {
            this.error("Unexpected failure during bean definition parsing", ele, var15);
        } finally {
            this.parseState.pop();
        }

        return null;
    }

通过对上述源码的分析，就会明白我们在Spring配置文件中元素的中配置的属性就是通过该方法解析和设置到Bean中去的。
注意：在解析元素过程中没有创建和实例化Bean对象，只是创建了Bean对象的定义类BeanDefinition，将元素中的配置信息设置到BeanDefinition中作为记录，当依赖注入时才使用这些记录信息创建和实例化具体的Bean对象。
上面方法中一些对一些配置如元信息(meta)、qualifier等的解析，我们在Spring中配置时使用的也不多，我们在使用Spring的元素时，配置最多的是属性。

调用BeanDefinitionReaderUtils的registerBeanDefinition方法向IoC容器注册解析的Bean

 protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if(bdHolder != null) {
            //通过对document对象的解析和封装返回一个BeanDefinitionHolder
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);

            try {
                //通过这个holder来注册bean对象
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
            } catch (BeanDefinitionStoreException var5) {
                this.getReaderContext().error("Failed to register bean definition with name "" + bdHolder.getBeanName() + """, ele, var5);
            }

            this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }

    }

当调用BeanDefinitionReaderUtils向IoC容器注册解析的BeanDefinition时，真正完成注册功能的是DefaultListableBeanFactory。

    public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException {
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
        String[] aliases = definitionHolder.getAliases();
        if(aliases != null) {
            String[] var4 = aliases;
            int var5 = aliases.length;

            for(int var6 = 0; var6 < var5; ++var6) {
                String alias = var4[var6];
                registry.registerAlias(beanName, alias);
            }
        }

    }

DefaultListableBeanFactory registerBeanDefinition方法

  //存储注册的俄BeanDefinition
 private final Map beanDefinitionMap = new ConcurrentHashMap(256);
 //向IoC容器注册解析的BeanDefiniton
 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");
        //校验解析的BeanDefiniton
        if(beanDefinition instanceof AbstractBeanDefinition) {
            try {
                ((AbstractBeanDefinition)beanDefinition).validate();
            } catch (BeanDefinitionValidationException var9) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var9);
            }
        }

        BeanDefinition oldBeanDefinition = (BeanDefinition)this.beanDefinitionMap.get(beanName);
        if(oldBeanDefinition != null) {
            if(!this.isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean "" + beanName + "": There is already [" + oldBeanDefinition + "] bound.");
            }

            if(oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                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(this.hasBeanCreationStarted()) {
                Map var4 = this.beanDefinitionMap;
                //注册的过程中需要线程同步，以保证数据的一致性 
                synchronized(this.beanDefinitionMap) {
                    //把bean存放到map中
                    this.beanDefinitionMap.put(beanName, beanDefinition);
                    List updatedDefinitions = new ArrayList(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    if(this.manualSingletonNames.contains(beanName)) {
                        Set updatedSingletons = new LinkedHashSet(this.manualSingletonNames);
                        updatedSingletons.remove(beanName);
                        this.manualSingletonNames = updatedSingletons;
                    }
                }
            } else {
                this.beanDefinitionMap.put(beanName, beanDefinition);
                this.beanDefinitionNames.add(beanName);
                this.manualSingletonNames.remove(beanName);
            }

            this.frozenBeanDefinitionNames = null;
        }

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

    }

至此，Bean定义资源文件中配置的Bean被解析过后，已经注册到IoC容器中，被容器管理起来，真正完成了IoC容器初始化所做的全部工作。现 在IoC容器中已经建立了整个Bean的配置信息，这些BeanDefinition信息已经可以使用，并且可以被检索，IoC容器的作用就是对这些注册的Bean定义信息进行处理和维护。这些的注册的Bean定义信息是IoC容器控制反转的基础，正是有了这些注册的数据，容器才可以进行依赖注入。