系列十五、BeanDefinition

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_INFRASTRUCTUREif (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 phasethis.beanDefinitionMap.put(beanName, beanDefinition);this.beanDefinitionNames.add(beanName);removeManualSingletonName(beanName);}this.frozenBeanDefinitionNames = null;}if (existingDefinition != null || containsSingleton(beanName)) {resetBeanDefinition(beanName);}
}