基于Java-based的Spring源码解读（九）

最新推荐文章于 2023-02-10 13:07:40 发布

zhaowei0720

最新推荐文章于 2023-02-10 13:07:40 发布

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分类专栏： Spring源码文章标签： spring java

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本文深入探讨了Spring框架中Bean定义的注册过程，详细分析了registerBeanDefinition方法的实现细节，包括验证BeanDefinition、处理BeanDefinition覆盖以及更新BeanDefinitionMap的过程。特别关注了在启动注册阶段的beanName和beanDefinition的简单存放操作。

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接着上一篇，上一篇讲到了，调用工具类注册后置处理器，主要做一些初始化工作，如初始化比较器、自动注入解析器及在Spring IOC容器内部与用户无关的一些解析器等。

今天分析下面这段代码

private static BeanDefinitionHolder registerPostProcessor(
		BeanDefinitionRegistry registry, RootBeanDefinition definition, String beanName) {
    definition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
    registry.registerBeanDefinition(beanName, definition);
    return new BeanDefinitionHolder(definition, beanName);
}

上段逻辑还是挺容易看懂的，设置RootBeanDefinition的角色，调用BeanDefinitionRegistry的注册bean定义的方法，将beanName注册容器（DefaultListableBeanFactory）

下面看一下registerBeanDefinition(beanName, definition)的逻辑

@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();
	}
}

可以看到这段代码的逻辑还是挺长的，这里先简单的解释下，因为现在仍然处在开始注册的阶段，实际执行的只有validate()及

下面这一段代码

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

可以看到，这个阶段只是简单的将beanName放到DefaultListableBeanFactory容器里