Spring源码解密之默认标签的解析

public class DefaultBeanDefinitionDocumentReader implements BeanDefinitionDocumentReader { private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) { // import 标签解析 if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) { importBeanDefinitionResource(ele); } // alias 标签解析 else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) { processAliasRegistration(ele); } // bean 标签解析 else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) { processBeanDefinition(ele, delegate); } // import 标签解析 else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) { // beans标签解析 递归方式  doRegisterBeanDefinitions(ele); } }}

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) { // 委托BeanDefinitionDelegate类的parseBeanDefinitionElement方法进行元素解析 BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); if (bdHolder != null) { // 当返回的bdHolder不为空的情况下若存在默认标签的子节点下再有自定义属性，还需要再次对自定义标签进行解析 bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); try { // 解析完成后需要对解析后的bdHolder进行注册，注册操作委托给了BeanDefinitionReaderUtils的registerBeanDefinition方法 BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry()); } catch (BeanDefinitionStoreException ex) { getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, ex); } // 最后发出响应事件，通知相关监听器这个bean已经被加载 getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder)); }}

public class BeanDefinitionParserDelegate { @Nullable public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) { // 获取Bean标签的ID属性 String id = ele.getAttribute(ID_ATTRIBUTE); // 获取Bean标签的Name属性 String nameAttr = ele.getAttribute(NAME_ATTRIBUTE); List<String> aliases = new ArrayList<>(); if (StringUtils.hasLength(nameAttr)) { // 将name属性的值通过,; 进行分割 转为字符串数字(即在配置文件中如配置多个name 在此做处理) String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS); aliases.addAll(Arrays.asList(nameArr)); } String beanName = id; // 如果ID为空 使用配置的第一个name属性作为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) { // 校验beanName和aliases的唯一性 // 内部核心为使用usedNames集合保存所有已经使用了的beanName和alisa checkNameUniqueness(beanName, aliases, ele); } // 进一步解析其他所有属性到GenericBeanDefinition对象中 AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean); if (beanDefinition != null) { // 如果bean没有指定beanName 那么使用默认规则为此Bean生成beanName 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); // 将信息封装到BeanDefinitionHolder对象中 return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray); } return null; }}

@Nullablepublic AbstractBeanDefinition parseBeanDefinitionElement( Element ele, String beanName, @Nullable BeanDefinition containingBean) { this.parseState.push(new BeanEntry(beanName)); // 获取Bean标签的class属性 String className = null; if (ele.hasAttribute(CLASS_ATTRIBUTE)) { className = ele.getAttribute(CLASS_ATTRIBUTE).trim(); } // 获取Bean标签的parent属性 String parent = null; if (ele.hasAttribute(PARENT_ATTRIBUTE)) { parent = ele.getAttribute(PARENT_ATTRIBUTE); } try { // 创建用于承载属性的AbstractBeanDefinition AbstractBeanDefinition bd = createBeanDefinition(className, parent); // 获取bean标签各种属性 parseBeanDefinitionAttributes(ele, beanName, containingBean, bd); // 解析description标签 bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT)); // 解析meta标签 parseMetaElements(ele, bd); // 解析lookup-method标签 parseLookupOverrideSubElements(ele, bd.getMethodOverrides()); // 解析replaced-method标签 parseReplacedMethodSubElements(ele, bd.getMethodOverrides()); // 解析constructor-arg标签 parseConstructorArgElements(ele, bd); // 解析property标签 parsePropertyElements(ele, bd); // 解析qualifier标签 parseQualifierElements(ele, bd); bd.setResource(this.readerContext.getResource()); bd.setSource(extractSource(ele)); return bd; } catch (ClassNotFoundException ex) { error("Bean class [" + className + "] not found", ele, ex); } catch (NoClassDefFoundError err) { error("Class that bean class [" + className + "] depends on not found", ele, err); } catch (Throwable ex) { error("Unexpected failure during bean definition parsing", ele, ex); } finally { this.parseState.pop(); } return null;}

// BeanDefinitionParserDelegate.javaprotected AbstractBeanDefinition createBeanDefinition(@Nullable String className, @Nullable String parentName) throws ClassNotFoundException { return BeanDefinitionReaderUtils.createBeanDefinition( parentName, className, this.readerContext.getBeanClassLoader());}public class BeanDefinitionReaderUtils { public static AbstractBeanDefinition createBeanDefinition( @Nullable String parentName, @Nullable String className, @Nullable ClassLoader classLoader) throws ClassNotFoundException { GenericBeanDefinition bd = new GenericBeanDefinition(); // parentName可能为空 bd.setParentName(parentName); // 如果classLoader不为空  // 则使用传入的classLoader同一虚拟机加载类对象 否则只记录classLoader if (className != null) { if (classLoader != null) { bd.setBeanClass(ClassUtils.forName(className, classLoader)); } else { bd.setBeanClassName(className); } } return bd; }}

public class BeanDefinitionParserDelegate { public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName, @Nullable BeanDefinition containingBean, AbstractBeanDefinition bd) { // ...省略详细代码，该部分代码主要就是通过 if else 判断是否含有指定的属性，如果有就 bd.set(attribute); return bd; }}```

``` java// BeanDefinitionParserDelegate.java@Nullablepublic BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) { // ... return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);}

public class BeanDefinitionReaderUtils { public static void registerBeanDefinition( BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException { // 使用 beanName 做唯一标识符 String beanName = definitionHolder.getBeanName(); // 注册bean的核心代码 registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition()); // 为bean注册所有的别名 String[] aliases = definitionHolder.getAliases(); if (aliases != null) { for (String alias : aliases) { registry.registerAlias(beanName, alias); } } }}

public class DefaultListableBeanFactory { @Override public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException { Assert.hasText(beanName, "Bean name must not be empty"); Assert.notNull(beanDefinition, "BeanDefinition must not be null"); if (beanDefinition instanceof AbstractBeanDefinition) { try { // 注册前的最后一次校验，这里的校验不同于XML文件校验 // 主要是对于AbstractBeanDefinition属性中的methodOverrides校验 // 校验methodOverrides是否与工厂方法并存或者methodOverrides对于的方法根本不存在 ((AbstractBeanDefinition) beanDefinition).validate(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", ex); } } BeanDefinition oldBeanDefinition; // 获取缓存中的 beanDefinition oldBeanDefinition = this.beanDefinitionMap.get(beanName); if (oldBeanDefinition != null) { // 如果缓存中存在 判断是否允许覆盖 if (!isAllowBeanDefinitionOverriding()) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound."); } else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) { // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE if (this.logger.isWarnEnabled()) { this.logger.warn("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } else if (!beanDefinition.equals(oldBeanDefinition)) { if (this.logger.isInfoEnabled()) { this.logger.info("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } else { if (this.logger.isDebugEnabled()) { this.logger.debug("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } // 如果允许覆盖，保存beanDefinition到beanDefinitionMap中 this.beanDefinitionMap.put(beanName, beanDefinition); } else { // 判断是否已经开始创建bean if (hasBeanCreationStarted()) { // Cannot modify startup-time collection elements anymore (for stable iteration) synchronized (this.beanDefinitionMap) { // 保存beanDefinition到beanDefinitionMap中 this.beanDefinitionMap.put(beanName, beanDefinition); // 更新已经注册的beanName List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1); updatedDefinitions.addAll(this.beanDefinitionNames); updatedDefinitions.add(beanName); this.beanDefinitionNames = updatedDefinitions; if (this.manualSingletonNames.contains(beanName)) { Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames); updatedSingletons.remove(beanName); this.manualSingletonNames = updatedSingletons; } } } else { // 还没开始创建bean this.beanDefinitionMap.put(beanName, beanDefinition); this.beanDefinitionNames.add(beanName); this.manualSingletonNames.remove(beanName); } this.frozenBeanDefinitionNames = null; } if (oldBeanDefinition != null || containsSingleton(beanName)) { // 重置beanName对应的缓存 resetBeanDefinition(beanName); } }}

public class SimpleAliasRegistry { /** Map from alias to canonical name */ private final Map<String, String> aliasMap = new ConcurrentHashMap<>(16); public void registerAlias(String name, String alias) { Assert.hasText(name, "'name' must not be empty"); Assert.hasText(alias, "'alias' must not be empty"); if (alias.equals(name)) {  // 如果beanName与alias相同的话不记录alias 并删除对应的alias  this.aliasMap.remove(alias); } else {  String registeredName = this.aliasMap.get(alias);  if (registeredName != null) {  if (registeredName.equals(name)) {   // 如果别名已经注册过并且指向的name和当前name相同 不做任何处理   return;  }  // 如果alias不允许被覆盖则抛出异常  if (!allowAliasOverriding()) {   throw new IllegalStateException("Cannot register alias '" + alias + "' for name '" + name + "': It is already registered for name '" + registeredName + "'.");  }  }  // 校验循环指向依赖 如A->B B->C C->A则出错  checkForAliasCircle(name, alias);  this.aliasMap.put(alias, name); } }}

protected void checkForAliasCircle(String name, String alias) { if (hasAlias(alias, name)) { throw new IllegalStateException("Cannot register alias '" + alias + "' for name '" + name + "': Circular reference - '" + name + "' is a direct or indirect alias for '" + alias + "' already"); }}public boolean hasAlias(String name, String alias) { for (Map.Entry<String, String> entry : this.aliasMap.entrySet()) { String registeredName = entry.getValue(); if (registeredName.equals(name)) { String registeredAlias = entry.getKey(); return (registeredAlias.equals(alias) || hasAlias(registeredAlias, alias)); } } return false;}

//DefaultBeanDefinitionDocumentReader.javaprotected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) { // Send registration event. getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));}

public class DefaultBeanDefinitionDocumentReader { protected void processAliasRegistration(Element ele) { // 获取 alisa 标签 name 属性 String name = ele.getAttribute(NAME_ATTRIBUTE); // 获取 alisa 标签 alias 属性 String alias = ele.getAttribute(ALIAS_ATTRIBUTE); boolean valid = true; if (!StringUtils.hasText(name)) {  getReaderContext().error("Name must not be empty", ele);  valid = false; } if (!StringUtils.hasText(alias)) {  getReaderContext().error("Alias must not be empty", ele);  valid = false; } if (valid) {  try {  // 进行别名注册  getReaderContext().getRegistry().registerAlias(name, alias);  } catch (Exception ex) {  getReaderContext().error("Failed to register alias '" + alias +   "' for bean with name '" + name + "'", ele, ex);  }  // 别名注册后告知监听器做相应处理  getReaderContext().fireAliasRegistered(name, alias, extractSource(ele)); } }}

public class DefaultBeanDefinitionDocumentReader { protected void importBeanDefinitionResource(Element ele) { // 获取import标签的resource属性 String location = ele.getAttribute(RESOURCE_ATTRIBUTE); // 如果不存在则不做任何处理 if (!StringUtils.hasText(location)) {  getReaderContext().error("Resource location must not be empty", ele);  return; } // 解析占位符属性 格式如"${user.dir}" location = getReaderContext().getEnvironment().resolveRequiredPlaceholders(location); Set<Resource> actualResources = new LinkedHashSet<>(4); // 判断资源是绝对路径还是相对路径 boolean absoluteLocation = false; try {  absoluteLocation = ResourcePatternUtils.isUrl(location) || ResourceUtils.toURI(location).isAbsolute(); } catch (URISyntaxException ex) {  // cannot convert to an URI, considering the location relative  // unless it is the well-known Spring prefix "classpath*:" }  // 如果是绝对路径则直接根据地址加载对应的配置文件 if (absoluteLocation) {  try {  int importCount = getReaderContext().getReader().loadBeanDefinitions(location, actualResources);  if (logger.isDebugEnabled()) {   logger.debug("Imported " + importCount + " bean definitions from URL location [" + location + "]");  }  } catch (BeanDefinitionStoreException ex) {  getReaderContext().error("Failed to import bean definitions from URL location [" + location + "]", ele, ex);  } } else {  try {  int importCount;  // 根据相对路径加载资源  Resource relativeResource = getReaderContext().getResource().createRelative(location);  if (relativeResource.exists()) {   importCount = getReaderContext().getReader().loadBeanDefinitions(relativeResource);   actualResources.add(relativeResource);  } else {   String baseLocation = getReaderContext().getResource().getURL().toString();   importCount = getReaderContext().getReader().loadBeanDefinitions(StringUtils.applyRelativePath(baseLocation, location), actualResources);  }  if (logger.isDebugEnabled()) {   logger.debug("Imported " + importCount + " bean definitions from relative location [" + location + "]");  }  } catch (IOException ex) {  getReaderContext().error("Failed to resolve current resource location", ele, ex);  } catch (BeanDefinitionStoreException ex) {  getReaderContext().error("Failed to import bean definitions from relative location [" + location + "]", ele, ex);  } } // 解析后进行监听器激活处理 Resource[] actResArray = actualResources.toArray(new Resource[actualResources.size()]); getReaderContext().fireImportProcessed(location, actResArray, extractSource(ele)); }}