Spring 中 Bean 注册疑问

[liuyunlong]

DefaultListableBeanFactory #registerBeanDefinition(String beanName,BeanDefintion bean);

疑问 1：

	@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 {
				((AbstractBeanDefinition) beanDefinition).validate();
			}
			catch (BeanDefinitionValidationException ex) {
				throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
						"Validation of bean definition failed", ex);
			}
		}

		BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
		if (existingDefinition != null) {
			if (!isAllowBeanDefinitionOverriding()) {
				throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
			}
			else if (existingDefinition.getRole() < beanDefinition.getRole()) {
				// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
				if (logger.isInfoEnabled()) {
					logger.info("Overriding user-defined bean definition for bean '" + beanName +
							"' with a framework-generated bean definition: replacing [" +
							existingDefinition + "] with [" + beanDefinition + "]");
				}
			}
			else if (!beanDefinition.equals(existingDefinition)) {
				if (logger.isDebugEnabled()) {
					logger.debug("Overriding bean definition for bean '" + beanName +
							"' with a different definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			else {
				if (logger.isTraceEnabled()) {
					logger.trace("Overriding bean definition for bean '" + beanName +
							"' with an equivalent definition: replacing [" + existingDefinition +
							"] with [" + beanDefinition + "]");
				}
			}
			this.beanDefinitionMap.put(beanName, beanDefinition);
		}
		else {
			if (hasBeanCreationStarted()) {
				// Cannot modify startup-time collection elements anymore (for stable iteration)
				synchronized (this.beanDefinitionMap) {
					this.beanDefinitionMap.put(beanName, beanDefinition);
					List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
					updatedDefinitions.addAll(this.beanDefinitionNames);
					updatedDefinitions.add(beanName);
					this.beanDefinitionNames = updatedDefinitions;
					removeManualSingletonName(beanName);
				}
			}
			else {
				// Still in startup registration phase
				this.beanDefinitionMap.put(beanName, beanDefinition);
				this.beanDefinitionNames.add(beanName);
				removeManualSingletonName(beanName);
			}
			this.frozenBeanDefinitionNames = null;
		}

		if (existingDefinition != null || containsSingleton(beanName)) {
			resetBeanDefinition(beanName);
		}
		else if (isConfigurationFrozen()) {
			clearByTypeCache();
		}
	}

其中这一段代码

	if (hasBeanCreationStarted()) {
				// Cannot modify startup-time collection elements anymore (for stable iteration)
				synchronized (this.beanDefinitionMap) {
					this.beanDefinitionMap.put(beanName, beanDefinition);
					List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
					updatedDefinitions.addAll(this.beanDefinitionNames);
					updatedDefinitions.add(beanName);
					this.beanDefinitionNames = updatedDefinitions;
					removeManualSingletonName(beanName);
				}
			}

不太明白为啥还得判断容器是否存活，但是断点下来确实走的 else

	else {
			// Still in startup registration phase
			this.beanDefinitionMap.put(beanName, beanDefinition);
			this.beanDefinitionNames.add(beanName);
			removeManualSingletonName(beanName);
		}

希望大家能给解答一下，万分感谢 ！

[shanghai1943]

claude ai 的回复


hasBeanCreationStarted() 方法是用来判断 bean 定义注册是否处于启动阶段。

在 Spring 容器启动时,会有一个 bean 定义注册的过程,这个过程称为启动阶段。启动阶段结束后,会调用 finishBeanFactoryInitialization() 方法,设置启动阶段完成的标记。

之所以需要判断启动阶段,是因为在启动阶段和非启动阶段,bean 定义的注册逻辑有略微不同:

1. 启动阶段:可以直接修改 beanDefinitionMap 和 beanDefinitionNames

2. 非启动阶段:需要同步处理,避免多线程并发访问这些容器内存状态

else 分支就是处理非启动阶段的逻辑。当容器已经完成了启动,这个时候再注册 bean 定义,就需要加锁处理:

1. 同步包装 beanDefinitionMap 的修改

2. 创建 beanDefinitionNames 的拷贝进行修改

3. 删除 manualSingletonNames 里的对应名称

之所以这么设计,是因为启动阶段内存状态的变更频繁,如果都加锁处理会非常低效。所以启动阶段只 simply 修改状态,结束后再对状态变更加锁。

而 hasBeanCreationStarted()就是判断当前是否还在启动阶段,从而决定走哪种 bean 定义注册逻辑。

所以这个判断对提高整个容器的并发性能很重要。

[liuyunlong]

清晰明了，万分感谢