BeanDefinition

• BeanDefinition 主要是 Bean 的描述信息。在ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();方法执行的时候，会调用到该方法。

/**
* BeanDefinition 的数据 
*/
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;
}

registerBeanDefinitions

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);
   // http://www.springframework.org/schema/beans, 为默认的 bean 的 namespace
   if (this.delegate.isDefaultNamespace(root)) {
      // PROFILE_ATTRIBUTE = profile， 表示获取 profile 标签
      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;
}

parseBeanDefinitions(root, this.delegate): 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)) {
               parseDefaultElement(ele, delegate);
            }
            else {
               delegate.parseCustomElement(ele);
            }
         }
      }
   }
   else {
      delegate.parseCustomElement(root);
   }
}

parseDefaultElement(ele, delegate): 方法

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

processBeanDefinition(ele, delegate)：bean 标签的解析

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.
         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));
   }
}

delegate.docorateBeanDefinitionIfRequire(ele, bdHolder)

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
   return parseBeanDefinitionElement(ele, null);
}

parseBeanDefiitionElement: 对 bean 的真正解析

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
   String id = ele.getAttribute(ID_ATTRIBUTE);
   String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
   List<String> aliases = new ArrayList<>();
   if (StringUtils.hasLength(nameAttr)) {
      String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
      aliases.addAll(Arrays.asList(nameArr));
   }
   String beanName = id;
   if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
      beanName = aliases.remove(0);
      if (logger.isDebugEnabled()) {
         logger.debug("No XML 'id' specified - using '" + beanName +
               "' as bean name and " + aliases + " as aliases");
      }
   }
   if (containingBean == null) {
      checkNameUniqueness(beanName, aliases, ele);
   }
   AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
   if (beanDefinition != null) {
      if (!StringUtils.hasText(beanName)) {
         try {
            if (containingBean != null) {
               beanName = BeanDefinitionReaderUtils.generateBeanName(
                     beanDefinition, this.readerContext.getRegistry(), true);
            }
            else {
               beanName = this.readerContext.generateBeanName(beanDefinition);
               // Register an alias for the plain bean class name, if still possible,
               // if the generator returned the class name plus a suffix.
               // This is expected for Spring 1.2/2.0 backwards compatibility.
               String beanClassName = beanDefinition.getBeanClassName();
               if (beanClassName != null &&
                     beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
                     !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                  aliases.add(beanClassName);
               }
            }
            if (logger.isDebugEnabled()) {
               logger.debug("Neither XML 'id' nor 'name' specified - " +
                     "using generated bean name [" + beanName + "]");
            }
         }
         catch (Exception ex) {
            error(ex.getMessage(), ele);
            return null;
         }
      }
      String[] aliasesArray = StringUtils.toStringArray(aliases);
      return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
   }
   return null;
}

这里就是真正的对 xml 各项参数进行处理了。