SpringIOC源码阅读笔记（4）

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原创最新推荐文章于 2026-03-19 01:16:39 发布 263 阅读 AI 写同款· GEO 优化 ›

Spring中Bean的生命周期源码分析从服务的启动到服务的关闭整个流程下来梳理了Bean的整个生命周期，根据这个生命周期自己可以根据这个流程对Spring中容器的实现和Bean的注入流程有了更深的了解，更多细节的部分可以根据一下的源码流程进行debug，毕竟debug看源码是最快的，debug的方式可以知道在每一步入参和出参的结果，以及每一步的正向流程。阅读详情

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));
		}
	}