接上篇【】 ，我們看到BeanDefinitionReader解決的是從資源文件（xml,propert）到BeanDefinition集合的過程。所以BeanDefinitionReader接口有兩個實現版本。
BeanDefinitionReader的接口聲明，ResourceLoader是spring中解決Resource加載的操作。四個loadBeanDefinitions就是重載解決單個或者多個資源文件的處理問題。
loadBeanDefinitions 是加載BeanDefinition接口的核心入口，AbstractBeanDefinitionReader中剩下了loadBeanDefinitions(Resource resource)這個方法給子類實現。
開始加載資源文件，這一步會將Resource構造為一個EncodedResource，添加了編碼的相關控制信息。
1 //XmlBeanDefinitionReader.java 2 public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException { 3 return loadBeanDefinitions(new EncodedResource(resource)); 4 }
下一步需要去判斷當前配置文件是否被循環加載。
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()); } //沒有明白為什么需要使用ThreadLoacal? //private final ThreadLocal<Set<EncodedResource>> resourcesCurrentlyBeingLoaded = new NamedThreadLocal<Set<EncodedResource>>("XML bean definition resources currently being loaded"); 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(); } } }
真正執行加載操作的是doLoadBeanDefinitions方法。
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { try { //獲取xml的校驗格式，dtd或者xsd的校驗模式 int validationMode = getValidationModeForResource(resource);
//解析xml為dom，用了sax解析的 Document doc = this.documentLoader.loadDocument( inputSource, getEntityResolver(), this.errorHandler, validationMode, isNamespaceAware());
//真正的主角來了 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); } }
spring解析xml文件為org.w3c.dom.Document使用了SAX的實現方法，除了SAX，常用的xml解析方法還有dom，dom4j，jdom等方法。
registerBeanDefinitions是正式注冊BeanDefinition的地方，這里又引入了一個新的接口BeanDefinitionDocumentReader（定義如何解析dom為BeanDefinition）。
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
//創建一個解析器 BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
//設置上下文環境 documentReader.setEnvironment(this.getEnvironment()); int countBefore = getRegistry().getBeanDefinitionCount(); documentReader.registerBeanDefinitions(doc, createReaderContext(resource)); return getRegistry().getBeanDefinitionCount() - countBefore; }
解析的實現為reader.registerBeanDefinitions方法。
public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) { this.readerContext = readerContext; logger.debug("Loading bean definitions"); Element root = doc.getDocumentElement(); doRegisterBeanDefinitions(root); }
緩存readerContext，目的不清楚。直接parse
protected void doRegisterBeanDefinitions(Element root) { String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE); if (StringUtils.hasText(profileSpec)) { Assert.state(this.environment != null, "Environment must be set for evaluating profiles"); String[] specifiedProfiles = StringUtils.tokenizeToStringArray( profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS); if (!this.environment.acceptsProfiles(specifiedProfiles)) { return; } } // 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 = createHelper(this.readerContext, root, parent); preProcessXml(root); parseBeanDefinitions(root, this.delegate); postProcessXml(root); this.delegate = parent; }
preProcessXml和postProcessXml方法暫時留空，目的為了需要增加新的實現版本時候方便擴展。
protected void preProcessXml(Element root) { } protected void postProcessXml(Element root) { }
parseBeanDefinitions方法內將
protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
//判斷解析的BeanDefinition是spring定義的還是自定義擴展的 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); } }
對於spring定義的BeanDefinition的解析以beans , bean , import , alias開頭的四種bean，其他標示開始認為是自定義bean。自定義bean的解析機制都要從NamespaceHandler接口出發。Spring-core和Spring-beans包內就提供了如下這些實現。
下面是BeanDefinitionParserDelegate類中具體處理自定義bean的代碼，允許根據不同的nameSpaceUri查找當前應用下面定義的解析類
public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) { String namespaceUri = getNamespaceURI(ele); 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)); }
至此解析部分完成了。但是解析完成的BeanDefinition放到哪里了呢？看一個例子：
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) { BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); if (bdHolder != null) { bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); try { // Register the final decorated instance.
//真正執行注冊BeanDefinition的類 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)); } }
這樣解析加載注冊BeanDefinition 的任務就結束了。