系列十五、BeanDefinition-优快云博客

本文链接：https://blog.youkuaiyun.com/HelloWorld20161112/article/details/134611946

一、BeanDefinition

1.1、概述

BeanDefinition是一个接口，主要负责存储bean的定义信息，决定bean的生产方式，是一个定义态的bean，类似于说明书。后续BeanFactory就可以根据这些信息生产bean了。比如实例化：可以通过反射得到实例对象；比如：lazy，则不会在IOC加载的时候创建bean；

二、加载过程

说明：以下代码是基于JavaConfig的方式。

2.1、过程概览

BeanDefinition的加载链路非常长，很容易就把人绕晕了，需要耐心阅读，但是大的流程是不变的，即：启动IOC容器===>解析配置类===>注册为BeanDefinitionMap。

2.1.1、启动IOC容器

AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MySpringConfig.class);

2.1.2、解析配置类

# 第一步

# 第二步

# 第三步

# 第四步

# 第五步

# 第六步

2.1.3、注册为beanDefinitionMap

@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);
	}
}