SpringIOC源码阅读笔记（4）

上文讲到parsePropertySubElement，分析完这个方法，接着在parseBeanDefinitionElement向下分析：

public void parsePropertyElements(Element beanEle, BeanDefinition bd) {
		NodeList nl = beanEle.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (isCandidateElement(node) && nodeNameEquals(node, PROPERTY_ELEMENT)) {
				parsePropertyElement((Element) node, bd);
			}
		}
	}

public void parsePropertyElement(Element ele, BeanDefinition bd) {
    // 获取 name 属性
    String propertyName = ele.getAttribute(NAME_ATTRIBUTE);
    //如果没有name属性报错
    if (!StringUtils.hasLength(propertyName)) {
        error("Tag 'property' must have a 'name' attribute", ele);
        return;
    }
    //加入解析状态
    this.parseState.push(new PropertyEntry(propertyName));
    try {
        // 如果存在相同的 name ，报错
        if (bd.getPropertyValues().contains(propertyName)) {
            error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
            return;
        }
        // 解析属性值
        Object val = parsePropertyValue(ele, bd, propertyName);
        // 创建 PropertyValue 对象
        PropertyValue pv = new PropertyValue(propertyName, val);
        parseMetaElements(ele, pv);
        pv.setSource(extractSource(ele));
        // 添加到 PropertyValue 集合中
        bd.getPropertyValues().addPropertyValue(pv);
    } finally {
        this.parseState.pop();
    }
}

逻辑其实跟constructor-arg子元素步骤一样。
接下来是parseQualifierElements，如果类型注入产生歧义，可以用名字注入
方法都差不多

public void parseQualifierElements(Element beanEle, AbstractBeanDefinition bd) {
		NodeList nl = beanEle.getChildNodes();
		for (int i = 0; i < nl.getLength(); i++) {
			Node node = nl.item(i);
			if (isCandidateElement(node) && nodeNameEquals(node, QUALIFIER_ELEMENT)) {
				parseQualifierElement((Element) node, bd);
			}
		}
	}

public void parseQualifierElement(Element ele, AbstractBeanDefinition bd) {
//解析type属性
		String typeName = ele.getAttribute(TYPE_ATTRIBUTE);
		if (!StringUtils.hasLength(typeName)) {
			error("Tag 'qualifier' must have a 'type' attribute", ele);
			return;
		}
		this.parseState.push(new QualifierEntry(typeName));
		try {
			AutowireCandidateQualifier qualifier = new AutowireCandidateQualifier(typeName);
			qualifier.setSource(extractSource(ele));
			//// 解析 value 属性，并设置到 AutowireCandidateQualifier 中
			String value = ele.getAttribute(VALUE_ATTRIBUTE);
			if (StringUtils.hasLength(value)) {
				qualifier.setAttribute(AutowireCandidateQualifier.VALUE_KEY, value);
			}
			NodeList nl = ele.getChildNodes();
			for (int i = 0; i < nl.getLength(); i++) {
				Node node = nl.item(i);
				if (isCandidateElement(node) && nodeNameEquals(node, QUALIFIER_ATTRIBUTE_ELEMENT)) {
					Element attributeEle = (Element) node;
					String attributeName = attributeEle.getAttribute(KEY_ATTRIBUTE);
					String attributeValue = attributeEle.getAttribute(VALUE_ATTRIBUTE);
					if (StringUtils.hasLength(attributeName) && StringUtils.hasLength(attributeValue)) {
						BeanMetadataAttribute attribute = new BeanMetadataAttribute(attributeName, attributeValue);
						attribute.setSource(extractSource(attributeEle));
						qualifier.addMetadataAttribute(attribute);
					}
					else {
						error("Qualifier 'attribute' tag must have a 'name' and 'value'", attributeEle);
						return;
					}
				}
			}
			// 添加到 qualifiers 中
			bd.addQualifier(qualifier);
		}
		finally {
			this.parseState.pop();
		}
	}

至此，已经完成了Document到BeanDefinitionHolder的转变。
沿着processBeanDefinition方法，下一步到了

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

这是关于自定义标签的解析，

public BeanDefinitionHolder decorateBeanDefinitionIfRequired(
			Element ele, BeanDefinitionHolder definitionHolder, @Nullable BeanDefinition containingBd) {

		BeanDefinitionHolder finalDefinition = definitionHolder;

		// Decorate based on custom attributes first.
		NamedNodeMap attributes = ele.getAttributes();
		//遍历属性，查看是否有适用于装饰的属性
		for (int i = 0; i < attributes.getLength(); i++) {
			Node node = attributes.item(i);
			finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
		}

		// Decorate based on custom nested elements.
		//遍历子节点，查看是否有适用于修饰的【子节点】
		NodeList children = ele.getChildNodes();
		for (int i = 0; i < children.getLength(); i++) {
			Node node = children.item(i);
			if (node.getNodeType() == Node.ELEMENT_NODE) {
				finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
			}
		}
		return finalDefinition;
	}

	public BeanDefinitionHolder decorateIfRequired(
			Node node, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {
		//获取自定义标签的命名空间
		String namespaceUri = getNamespaceURI(node);
		//如果是默认命名标签，直接过滤
		if (namespaceUri != null && !isDefaultNamespace(namespaceUri)) {
		//找到对应的处理器
			NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
			//进行修饰处理，具体修饰处理见下文中的自定义处理
			if (handler != null) {
				BeanDefinitionHolder decorated =
						handler.decorate(node, originalDef, new ParserContext(this.readerContext, this, containingBd));
				if (decorated != null) {
					return decorated;
				}
			}
			else if (namespaceUri.startsWith("http://www.springframework.org/")) {
				error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", node);
			}
			else {
				// A custom namespace, not to be handled by Spring - maybe "xml:...".
				if (logger.isDebugEnabled()) {
					logger.debug("No Spring NamespaceHandler found for XML schema namespace [" + namespaceUri + "]");
				}
			}
		}
		return originalDef;
	}

接下来是注册解析的BeanDefinition环节：

public static void registerBeanDefinition(
			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
			throws BeanDefinitionStoreException {

		// Register bean definition under primary name.
		//注册beanName
		String beanName = definitionHolder.getBeanName();
		registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

		// Register aliases for bean name, if any.
		//注册alias
		String[] aliases = definitionHolder.getAliases();
		if (aliases != null) {
			for (String alias : aliases) {
				registry.registerAlias(beanName, alias);
			}
		}
	}

注册beanName

@Override
private boolean allowBeanDefinitionOverriding = true;

/** 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);
/** Cached array of bean definition names in case of frozen configuration. */
@Nullable
private volatile String[] frozenBeanDefinitionNames;
	public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
			throws BeanDefinitionStoreException {
		//校验 beanName 与 beanDefinition 非空
		Assert.hasText(beanName, "Bean name must not be empty");
		Assert.notNull(beanDefinition, "BeanDefinition must not be null");

		if (beanDefinition instanceof AbstractBeanDefinition) {
			try {
			//校验 BeanDefinition
				((AbstractBeanDefinition) beanDefinition).validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}

		BeanDefinition oldBeanDefinition;
		//从缓存中获取指定 beanName 的 BeanDefinition
		oldBeanDefinition = this.beanDefinitionMap.get(beanName);
		
		if (oldBeanDefinition != null) {
		//如果存在但是不允许覆盖，抛出异常
			if (!isAllowBeanDefinitionOverriding()) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
						"': There is already [" + oldBeanDefinition + "] bound.");
			}
			//覆盖 beanDefinition 大于 被覆盖的 beanDefinition 的 ROLE ，打印 info 日志
			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 + "]");
				}
			}
			//// 覆盖 beanDefinition 与 被覆盖的 beanDefinition 不相同，打印 debug 日志
			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 + "]");
				}
			}
			// 其它，打印 debug 日志
			else {
				if (this.logger.isDebugEnabled()) {
					this.logger.debug("Overriding bean definition for bean '" + beanName +
							"' with an equivalent definition: replacing [" + oldBeanDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			// 允许覆盖，直接覆盖原有的 BeanDefinition 到 beanDefinitionMap 中
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		else {
		//检测创建Bean阶段是否已经开启，如果开启了就需要对beanDefinitionMap 进行并发控制
			if (hasBeanCreationStarted()) {
				// Cannot modify startup-time collection elements anymore (for stable iteration)
				synchronized (this.beanDefinitionMap) {
				// 添加到 BeanDefinition 到 beanDefinitionMap 中。
					this.beanDefinitionMap.put(beanName, beanDefinition);
					// 添加 beanName 到 beanDefinitionNames 中
					List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
					updatedDefinitions.addAll(this.beanDefinitionNames);
					updatedDefinitions.add(beanName);
					this.beanDefinitionNames = updatedDefinitions;
					// 从 manualSingletonNames 移除 beanName
					if (this.manualSingletonNames.contains(beanName)) {
						Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
						updatedSingletons.remove(beanName);
						this.manualSingletonNames = updatedSingletons;
					}
				}
			}
			else {
				// Still in startup registration phase
				this.beanDefinitionMap.put(beanName, beanDefinition);
				this.beanDefinitionNames.add(beanName);
				this.manualSingletonNames.remove(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}
		//重新设置 beanName 对应的缓存
		if (oldBeanDefinition != null || containsSingleton(beanName)) {
			resetBeanDefinition(beanName);
		}
	}

@Override
	public void registerAlias(String name, String alias) {
		Assert.hasText(name, "'name' must not be empty");
		Assert.hasText(alias, "'alias' must not be empty");
		// name == alias 则去掉alias
		if (alias.equals(name)) {
			this.aliasMap.remove(alias);
		}
		else {
		// 获取 alias 已注册的 beanName
			String registeredName = this.aliasMap.get(alias);
			if (registeredName != null) {
			//无需重复注册
				if (registeredName.equals(name)) {
					// An existing alias - no need to re-register
					return;
				}
				//不相同且不允许覆盖，抛出错误
				if (!allowAliasOverriding()) {
					throw new IllegalStateException("Cannot register alias '" + alias + "' for name '" +
							name + "': It is already registered for name '" + registeredName + "'.");
				}
			}
			//检验是否有循环
			checkForAliasCircle(name, alias);
			//注册到map中
			this.aliasMap.put(alias, name);
		}
	}

三.alias

protected void processAliasRegistration(Element ele) {
		String name = ele.getAttribute(NAME_ATTRIBUTE);
		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 {
				getReaderContext().getRegistry().registerAlias(name, alias);
			}
			catch (Exception ex) {
				getReaderContext().error("Failed to register alias '" + alias +
						"' for bean with name '" + name + "'", ele, ex);
			}
			getReaderContext().fireAliasRegistered(name, alias, extractSource(ele));
		}
	}

原理其实跟刚才解析bean中的alias相同。

四.嵌入式beans标签

其实就是递归调用注册BeanDefinition。