spring 解析bean

**
     * 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)) {
　　　　　　　　　　　　　　//解析默认的标签
                        parseDefaultElement(ele, delegate);
                    }
                    else {
　　　　　　　　　　　　　　//解析custom标签
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

@Nullable
    public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
        String namespaceUri = getNamespaceURI(ele);
        if (namespaceUri == null) {
            return null;
        }
        NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
        if (handler == null) {
            error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
            return null;
        }
        return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
    }

    /**
     * Parses the supplied {@link Element} by delegating to the {@link BeanDefinitionParser} that is
     * registered for that {@link Element}.
     */
    @Override
    @Nullable
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        BeanDefinitionParser parser = findParserForElement(element, parserContext);
        return (parser != null ? parser.parse(element, parserContext) : null);
    }

@Override
    @Nullable
    public BeanDefinition parse(Element element, ParserContext parserContext) {
　　　　　　//获取扫描哪个包
        String basePackage = element.getAttribute(BASE_PACKAGE_ATTRIBUTE);
        basePackage = parserContext.getReaderContext().getEnvironment().resolvePlaceholders(basePackage);
        String[] basePackages = StringUtils.tokenizeToStringArray(basePackage,
                ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);

        // Actually scan for bean definitions and register them.
        ClassPathBeanDefinitionScanner scanner = configureScanner(parserContext, element);
        Set<BeanDefinitionHolder> beanDefinitions = scanner.doScan(basePackages);
　　　　　　　　//注册容器
        registerComponents(parserContext.getReaderContext(), beanDefinitions, element);

        return null;
    }