spring加載bean定義

分析入口->loadBeanDefinitions

該邏輯的入口為：XmlBeanDefinitionReader.loadBeanDefinitions

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

        //resourcesCurrentlyBeingLoaded記錄已經(jīng)被加載過的資源
        Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
        if (currentResources == null) {
            currentResources = new HashSet<>(4);
            this.resourcesCurrentlyBeingLoaded.set(currentResources);
        }
        //如果已經(jīng)加載過，則拋出異常
        if (!currentResources.add(encodedResource)) {
            throw new BeanDefinitionStoreException(
                    "Detected cyclic loading of " + encodedResource + " - check your import definitions!");
        }
        try {
            InputStream inputStream = encodedResource.getResource().getInputStream();
            try {
                InputSource inputSource = new InputSource(inputStream);
                if (encodedResource.getEncoding() != null) {
                    inputSource.setEncoding(encodedResource.getEncoding());
                }
                //加載beandefenition的真正處理邏輯
                return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
            }
            finally {
                inputStream.close();
            }
        }
        catch (IOException ex) {
            throw new BeanDefinitionStoreException(
                    "IOException parsing XML document from " + encodedResource.getResource(), ex);
        }
        finally {
            currentResources.remove(encodedResource);
            if (currentResources.isEmpty()) {
                this.resourcesCurrentlyBeingLoaded.remove();
            }
        }
    }

該方法一共做了這么3件事：
1、判斷該資源是否已經(jīng)加載解析過，如果有，則拋出異常
2、將編碼處理過的Resource資源對(duì)象，轉(zhuǎn)成SAX可以解析的InputSource對(duì)象
3、將注冊(cè)的真正處理過程交給doLoadBeanDefinitions處理

驗(yàn)證加載xml并進(jìn)行解析注冊(cè)->doLoadBeanDefinitions

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
        throws BeanDefinitionStoreException {
        //....
        //進(jìn)行xml的驗(yàn)證并且加載
        Document doc = doLoadDocument(inputSource, resource);
        //進(jìn)行xml文檔對(duì)象的解析以及對(duì)BeanDefinition的注冊(cè)
        return registerBeanDefinitions(doc, resource);
        //...
}

這個(gè)方法做了2件事：
1、進(jìn)行xml的驗(yàn)證并且加載
2、將內(nèi)存的xml文檔對(duì)象解析并進(jìn)行注冊(cè)

registerBeanDefinitions

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
    //使用DefaultBeanDefinitionDocumentReader進(jìn)行解析
    BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    //記錄解析前BeanDefinition的個(gè)數(shù)
    int countBefore = getRegistry().getBeanDefinitionCount();
    //解析注冊(cè)
    documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    //返回解析之后的Beandefenition個(gè)數(shù)
    return getRegistry().getBeanDefinitionCount() - countBefore;
}

進(jìn)入到DefaultBeanDefinitionDocumentReader.registerBeanDefinitions

    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {
        this.readerContext = readerContext;
        logger.debug("Loading bean definitions");
        //獲取根節(jié)點(diǎn)對(duì)象
        Element root = doc.getDocumentElement();
        //解析注冊(cè)
        doRegisterBeanDefinitions(root);
    }

前面都是xml的驗(yàn)證以及加載過程，到這里，xml已經(jīng)轉(zhuǎn)化為對(duì)應(yīng)的Document對(duì)象了，開始進(jìn)入解析注冊(cè)階段。

解析注冊(cè)->doRegisterBeanDefinitions

protected void doRegisterBeanDefinitions(Element root) {
    //....
    parseBeanDefinitions(root, this.delegate);
    //....
}

節(jié)點(diǎn)元素解析->parseBeanDefinitions:

    protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
        //如果是缺省命名空間，進(jìn)行默認(rèn)解析注冊(cè)，否則進(jìn)行自定義元素解析方法
        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;
                    //循環(huán)遍歷節(jié)點(diǎn)，如果是默認(rèn)命名空間，則采取默認(rèn)標(biāo)簽解析方法，否則采用自定義標(biāo)簽解析方法
                    if (delegate.isDefaultNamespace(ele)) {
                        parseDefaultElement(ele, delegate);
                    }
                    else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        }
        else {
            delegate.parseCustomElement(root);
        }
    }

默認(rèn)標(biāo)簽解析->parseDefaultElement

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
    //對(duì)import標(biāo)簽的處理
    if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {
        importBeanDefinitionResource(ele);
    }
    //對(duì)alias標(biāo)簽處理
    else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {
        processAliasRegistration(ele);
    }
    //對(duì)bean標(biāo)簽處理
    else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {
        processBeanDefinition(ele, delegate);
    }
    //對(duì)beans標(biāo)簽處理
    else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {
        // recurse
        doRegisterBeanDefinitions(ele);
    }
}

以上提供了4種標(biāo)簽（import、alias、bean、beans）的解析方法，重點(diǎn)分析bean標(biāo)簽

解析bean標(biāo)簽：

    protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        //主要是對(duì)bean標(biāo)簽的屬性以及子節(jié)點(diǎn)進(jìn)行解析
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
            try {
                // Register the final decorated instance.
                //注冊(cè)BeanDefenition
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
            }
            catch (BeanDefinitionStoreException ex) {
                getReaderContext().error("Failed to register bean definition with name '" +
                        bdHolder.getBeanName() + "'", ele, ex);
            }
            // Send registration event.
            getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }
    }

1、針對(duì)以下屬性及子節(jié)點(diǎn)進(jìn)行解析（部分省略）
默認(rèn)屬性：

1539004166366.png

1539004187590.png

默認(rèn)節(jié)點(diǎn)

1539004251385.png

2、將解析完成的BeanDefinition注冊(cè)到map中，見DefaultListableBeanFactory.registerBeanDefinition

    /** Map of bean definition objects, keyed by bean name */
    private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);

    /** List of bean definition names, in registration order */
    private volatile List<String> beanDefinitionNames = new ArrayList<>(256);
    
   /** List of names of manually registered singletons, in registration order */
    private volatile Set<String> manualSingletonNames = new LinkedHashSet<>(16);

    this.beanDefinitionMap.put(beanName, beanDefinition);
    this.beanDefinitionNames.add(beanName);
    this.manualSingletonNames.remove(beanName);

如圖為解析注冊(cè)完成之后的BeanDefinition：

1539005228089.png

至此，bean標(biāo)簽的解析注冊(cè)結(jié)束，在這個(gè)過程中，沒有細(xì)致分析bean標(biāo)簽解析的相關(guān)細(xì)節(jié)，只是大概知道它有哪些屬性以及子節(jié)點(diǎn)，更多細(xì)節(jié)問題還需在使用過程中了解，并再結(jié)合源碼深入分析。