上一篇博客說(shuō)明了下spring是如何找到資源文件的觉壶，classpath下的xml，最終會(huì)被解析為 ClassPathContextResource，下面進(jìn)一步分析虎忌，有了這個(gè)資源文件之后spring是如何將其解析為BeanDefinition的

入口XmlBeanDefinitionReader.loadBeanDefinitions

最開(kāi)始的入口归粉，只是包了下Resource

public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
    //EncodedResource只是存了Resource的編碼
    return loadBeanDefinitions(new EncodedResource(resource));
}

1）保存當(dāng)前正在加載的資源
2）檢測(cè)是否有重復(fù)加載資源的情況
3）真正干活的地方doLoadBeanDefinitions

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
    
    //... 省略日志

    //1年堆、保存當(dāng)前正在加載的資源
    Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
    if (currentResources == null) {
        currentResources = new HashSet<>(4);
        this.resourcesCurrentlyBeingLoaded.set(currentResources);
    }

    //2、檢測(cè)是否有重復(fù)加載資源的情況
    if (!currentResources.add(encodedResource)) {
        throw new BeanDefinitionStoreException(
                "Detected cyclic loading of " + encodedResource + " - check your import definitions!");
    }

    InputStream inputStream = encodedResource.getResource().getInputStream();
    try {
        //document加載需要的的InputSource
        InputSource inputSource = new InputSource(inputStream);
        if (encodedResource.getEncoding() != null) {
            inputSource.setEncoding(encodedResource.getEncoding());
        }
        //3盏浇、真正干活的地方doLoadBeanDefinitions
        return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
    }
    finally {
        inputStream.close();
    }

    //... 省略 一系列異常處理
}

1变丧、這里做的兩件事，將資源文件解析成Document
2绢掰、解析并注冊(cè)BeanDefinitions

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
        throws BeanDefinitionStoreException {
    
    Document doc = doLoadDocument(inputSource, resource);
    return registerBeanDefinitions(doc, resource);
    
}

protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
    return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
            getValidationModeForResource(resource), isNamespaceAware());
}

document的解析

XmlBeanDefinitionReader 將 Document的生成痒蓬，委托給了DocumentLoader

看下默認(rèn)實(shí)現(xiàn) DefaultDocumentLoader

@Override
public Document loadDocument(InputSource inputSource, EntityResolver entityResolver,
        ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {

    //模板方法模式，子類繼承DefaultDocumentLoader后可以替換DocumentBuilderFactory和DocumentBuilder的實(shí)現(xiàn)
    DocumentBuilderFactory factory = createDocumentBuilderFactory(validationMode, namespaceAware);
    if (logger.isDebugEnabled()) {
        logger.debug("Using JAXP provider [" + factory.getClass().getName() + "]");
    }
    DocumentBuilder builder = createDocumentBuilder(factory, entityResolver, errorHandler);
    return builder.parse(inputSource);
}

這里使用了工廠方法模式

解析xml 并 注冊(cè)BeanDefinition

有了document之后滴劲，就可以很方便的通過(guò)document的API來(lái)讀取xml的元素攻晒。

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
    BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    int countBefore = getRegistry().getBeanDefinitionCount();
    //beanDefininition的注冊(cè)，委托給了BeanDefnitionDocumentReader
    documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    return getRegistry().getBeanDefinitionCount() - countBefore;
}

具體的注冊(cè)調(diào)用過(guò)程班挖，就不跟了鲁捏，總之，最后會(huì)調(diào)用到org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader#parseBeanDefinitions方法

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)) {
                    //默認(rèn)標(biāo)簽的解析
                    parseDefaultElement(ele, delegate);
                }
                else {
                    delegate.parseCustomElement(ele);
                }
            }
        }
    }
    else {
        //自定義標(biāo)簽的解析
        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);
    }
}

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
    //import標(biāo)簽解析
    if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
        importBeanDefinitionResource(ele);
    }
    //alias標(biāo)簽解析
    else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
        processAliasRegistration(ele);
    }
    //bean標(biāo)簽
    else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
        processBeanDefinition(ele, delegate);
    }
    //beans標(biāo)簽
    else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
        // recurse
        doRegisterBeanDefinitions(ele);
    }
}

到了這一步萧芙，spring開(kāi)始配置文件解析给梅，具體如何解析，以及如何將配置文件封裝為BeanDefinitions并進(jìn)行注冊(cè)双揪，下一篇博客會(huì)分析动羽。