解析Spring源碼（7）--DefaultBeanDefinitionDocumentReader

            //獲取Document對象用於解析xml文檔,包含xml文檔的一些相關信息
            Document doc = doLoadDocument(inputSource, resource);
            //註冊bean，創建是當獲取的時候創建getBean("...");會將xml文件中的bean節點註冊保存
            return registerBeanDefinitions(doc, resource);

    /**
     * Register the bean definitions contained in the given DOM document.
     * Called by {@code loadBeanDefinitions}.
     * <p>Creates a new instance of the parser class and invokes
     * {@code registerBeanDefinitions} on it.
     * @param doc the DOM document
     * @param resource the resource descriptor (for context information)
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of parsing errors
     * @see #loadBeanDefinitions
     * @see #setDocumentReaderClass
     * @see BeanDefinitionDocumentReader#registerBeanDefinitions
     */
    public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        //創建DefaultBeanDefinitionDocumentReader對象documentReader 
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        int countBefore = getRegistry().getBeanDefinitionCount();
        //最終會給reader對象中的registry添加beanDefinition，beanName
        //createReaderContext(resource):new XmlReaderContext對象封裝resource
        //會將xml文件中的bean節點註冊保存
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }

    /**
     * Register the bean definitions contained in the given DOM document.
     * Called by {@code loadBeanDefinitions}.
     * <p>Creates a new instance of the parser class and invokes
     * {@code registerBeanDefinitions} on it.
     * @param doc the DOM document
     * @param resource the resource descriptor (for context information)
     * @return the number of bean definitions found
     * @throws BeanDefinitionStoreException in case of parsing errors
     * @see #loadBeanDefinitions
     * @see #setDocumentReaderClass
     * @see BeanDefinitionDocumentReader#registerBeanDefinitions
     */
    public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
        //創建DefaultBeanDefinitionDocumentReader對象documentReader ，利用反射機制。。。。？？？？
        BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
        int countBefore = getRegistry().getBeanDefinitionCount();
        //最終會給reader對象中的registry添加beanDefinition，beanName
        //createReaderContext(resource):new XmlReaderContext對象封裝resource
        //會將xml文件中的bean節點註冊保存
        documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
        return getRegistry().getBeanDefinitionCount() - countBefore;
    }

    /**
     * 會將xml文件中的bean節點註冊保存
     * This implementation parses bean definitions according to the "spring-beans" XSD
     * (or DTD, historically).
     * <p>Opens a DOM Document; then initializes the default settings
     * specified at the {@code <beans/>} level; then parses the contained bean definitions.
     */
    @Override
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        //根節點
        Element root = doc.getDocumentElement();
        doRegisterBeanDefinitions(root);
    }

    /**
     * Register each bean definition within the given root {@code <beans/>} element.
     */
    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;
        //創建一個對象，封裝了readerContext
        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);//空方法
        parseBeanDefinitions(root, this.delegate);
        postProcessXml(root);//空方法

        this.delegate = parent;
    }

    /**
     * Parse the elements at the root level in the document:
     * "import", "alias", "bean".
     * @param root the DOM root element of the document
     */
    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);//註冊，保存
        }
        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
            // recurse
            doRegisterBeanDefinitions(ele);
        }
    }

    /**
     * 註冊
     * 將String beanName, BeanDefinition beanDefinition添加進集合
     * registry.beanDefinitionMap.put(beanName, beanDefinition);
     * registry.beanDefinitionNames.add(beanName);
     * 
     * Process the given bean element, parsing the bean definition
     * and registering it with the registry.
     */
    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        //創建BeanDefinitionHolder對象包含屬性beanDefinition,beanName
        //封裝beanDefinition，beanName的BeanDefinitionHolder對象,節點屬性也一併讀取了
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            //������書�ܣ���beanDefinition����װ�Σ����ó���
            //<bean id="test" class="test.MyClass">
            //  <mybean:user username="aaa"/>
            //</bean>按下不表
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
                //將String beanName, BeanDefinition beanDefinition添加進集合
                //registry.beanDefinitionMap.put(beanName, beanDefinition);
                //registry.beanDefinitionNames.add(beanName);
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +
                        bdHolder.getBeanName() + "'", ele, ex);
            }
            // Send registration event.
            //new BeanComponentDefinition(bdHolder)封裝bdHolder中的屬性beanDefinition,beanName
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }