这篇文章分享一下spring IoC容器初始化第三部分的代码,也就是将前面解析得到的BeanDefinition注册进IoC容器,其实就是存入一个ConcurrentHashMap<String, BeanDefinition>中。
(PS:可以结合我GitHub上对spring框架源码的翻译注解一起看,会更有助于各位同学理解,地址:
spring-beans https://github.com/AmyliaY/spring-beans-reading
spring-context https://github.com/AmyliaY/spring-context-reading
)
1、回过头看一下前面在DefaultBeanDefinitionDocumentReader中实现的processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate)方法
// 解析Bean定义资源Document对象的普通元素
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// BeanDefinitionHolder是对BeanDefinition的封装,即BeanDefinition的封装类
// 对Document对象中<Bean>元素的解析由BeanDefinitionParserDelegate实现
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
// 对bdHolder进行包装处理
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
/**
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
* 向Spring IoC容器注册解析BeanDefinition,这是BeanDefinition向IoC容器注册的入口
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*/
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// 在完成向Spring IOC容器注册解析得到的Bean定义之后,发送注册事件
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
2、BeanDefinitionReaderUtils的registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)方法
// 将解析的BeanDefinitionHold注册到容器中
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// 获取解析的BeanDefinition的名称
String beanName = definitionHolder.getBeanName();
/**
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
* 开始向IOC容器注册BeanDefinition
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*/
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// 如果解析的BeanDefinition有别名,向容器为其注册别名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String aliase : aliases) {
registry.registerAlias(beanName, aliase);
}
}
}
3、BeanDefinitionRegistry中的registerBeanDefinition(String beanName, BeanDefinition beanDefinition)方法在DefaultListableBeanFactory实现类中的具体实现
// 向IoC容器注册解析的BeanDefinito
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");
// 校验解析的BeanDefiniton
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
// 注册的过程中需要线程同步,以保证数据的一致性
synchronized (this.beanDefinitionMap) {
Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
// 检查是否有同名的BeanDefinition已经在IOC容器中注册,如果已经注册,
// 并且不允许覆盖已注册的BeanDefinition,则抛出注册失败异常,
// allowBeanDefinitionOverriding默认为true
if (oldBeanDefinition != null) {
if (!this.allowBeanDefinitionOverriding) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else {// 如果允许覆盖,则同名的Bean,后注册的覆盖先注册的
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
}
else {// IOC容器中没有已经注册同名的Bean,按正常注册流程注册
this.beanDefinitionNames.add(beanName);
this.frozenBeanDefinitionNames = null;
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
// 重置所有已经注册过的BeanDefinition的缓存
resetBeanDefinition(beanName);
}
最后看一下spring的IoC容器在代码中最直接的体现
// 存储注册信息的BeanDefinition集合,也就是所谓的IoC容器
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);