SPRING源码学习之路（一）

结合《Spring技术内幕：深入解析SPRING架构与设计原理》这本书开启Spring学习之路。

ps:之前其实已经看过一部分了，但是也就是看过，一看而过了。o(╯□╰)o

结合FileSystemXmlApplicationContext来分析  具体实现如下：

//对象初始化时候 调用refresh()，启动了BeanDifinition载入过程public FileSystemXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)throws BeansException {super(parent);setConfigLocations(configLocations);if (refresh) {refresh();}}

refresh()方法的实现：

@Overridepublic void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// Prepare this context for refreshing.prepareRefresh();// 调用子类  refreshBeanFactoryConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();// 准备beanFactoryprepareBeanFactory(beanFactory);try {//设置beanFactory的后置处理.postProcessBeanFactory(beanFactory);// 调用beanFactory的后置处理器，这些后处理器是在Bean定义中向容器注册的invokeBeanFactoryPostProcessors(beanFactory);// 注册bean的后处理器，在bean创建过程中调用registerBeanPostProcessors(beanFactory);// 初始化上下文中的消息源initMessageSource();// 初始化事件机制initApplicationEventMulticaster();// 初始化其他特殊beanonRefresh();// 检测监听bean，并向容器注册registerListeners();// 实例化所有 (non-lazy-init) 单例finishBeanFactoryInitialization(beanFactory);// 发布容器事件，结束Refresh过程finishRefresh();}catch (BeansException ex) {logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);// 防止bean资源占用，在异常处理中，销毁已经在前面生成的bean单件destroyBeans();// Reset 'active' flag.cancelRefresh(ex);// Propagate exception to caller.throw ex;}finally {// Reset common introspection caches in Spring's core, since we// might not ever need metadata for singleton beans anymore...resetCommonCaches();}}}

IOC容器的启动，蕴含了BeanDefinition的Resource定位，载入，注册等三个过程

在refresh()方法中可以看到调用了子类 refreshBeanFactory()方法，在其子类AbstractRefreshableApplicationContext中的实现

@Overrideprotected final void refreshBeanFactory() throws BeansException {if (hasBeanFactory()) {destroyBeans();closeBeanFactory();}try {   //创建beanFactory 类型为DefaultListableBeanFactoryDefaultListableBeanFactory beanFactory = createBeanFactory();beanFactory.setSerializationId(getId());customizeBeanFactory(beanFactory);loadBeanDefinitions(beanFactory);// 启动对BeanDefinition的载入synchronized (this.beanFactoryMonitor) {this.beanFactory = beanFactory;}}catch (IOException ex) {throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);}}

loadBeanDefinitions的具体实现在AbstractRefreshableApplicationContext子类 AbstractXmlApplicationContext中，代码：

  

@Overrideprotected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {// Create a new XmlBeanDefinitionReader for the given BeanFactory.XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);// Configure the bean definition reader with this context's// resource loading environment.beanDefinitionReader.setEnvironment(this.getEnvironment());beanDefinitionReader.setResourceLoader(this);beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));// Allow a subclass to provide custom initialization of the reader,// 启动bean定义信息的载入过程.initBeanDefinitionReader(beanDefinitionReader);loadBeanDefinitions(beanDefinitionReader);}

可以看到 这里创建了XmlBeanDefinitionReader 设置到beanFactory 为reader配置resourceLoader

      接着就是loadBeanDefinitions调用地方

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

调用了reader也就是 XmlBeanDefinitionReader 的 loadBeanDefinitions方法

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

具体读取过程 在doLoadBeanDefinitions中实现

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)throws BeanDefinitionStoreException {try {                      // 获取XML文件document，解析过程由documentLoader完成Document doc = doLoadDocument(inputSource, resource);                         // 这里启动对BeanDefinition解析的详细过程return registerBeanDefinitions(doc, resource);}catch (BeanDefinitionStoreException ex) {throw ex;}catch (SAXParseException ex) {throw new XmlBeanDefinitionStoreException(resource.getDescription(),"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);}catch (SAXException ex) {throw new XmlBeanDefinitionStoreException(resource.getDescription(),"XML document from " + resource + " is invalid", ex);}catch (ParserConfigurationException ex) {throw new BeanDefinitionStoreException(resource.getDescription(),"Parser configuration exception parsing XML from " + resource, ex);}catch (IOException ex) {throw new BeanDefinitionStoreException(resource.getDescription(),"IOException parsing XML document from " + resource, ex);}catch (Throwable ex) {throw new BeanDefinitionStoreException(resource.getDescription(),"Unexpected exception parsing XML document from " + resource, ex);}}

我们重点关注 registerBeanDefinitions方法的具体实现

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();int countBefore = getRegistry().getBeanDefinitionCount();documentReader.registerBeanDefinitions(doc, createReaderContext(resource));return getRegistry().getBeanDefinitionCount() - countBefore;}

这里调用上面提到 documentReader 对应的registerBeanDefinitions方法

public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) {this.readerContext = readerContext;logger.debug("Loading bean definitions");Element root = doc.getDocumentElement();doRegisterBeanDefinitions(root);}

具体过程在doRegisterBeanDefinitions中实现

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;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);parseBeanDefinitions(root, this.delegate);postProcessXml(root);this.delegate = parent;}

可以看到其中创建了bean定义信息的解析代理类 具体解析过程在 parseBeanDefinitions中实现

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);}}

默认解析元素方法  parseDefaultElement

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)) {// recursedoRegisterBeanDefinitions(ele);}}

可以看到通过if else 对元素类型进行区分  ，我们重点关注 bean标签的解析过程

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);if (bdHolder != null) {bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);try {// 向IOC容器注册解析得到的beanDefinitionsBeanDefinitionReaderUtils.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));}}

这就是大体的载入过程

 大体流程图：