回顾上一篇博客中,在AbstractApplicationContext这个抽象类中,Spring使用invokeBeanFactoryPostProcessors(beanFactory);执行BeanFactoryPostProcessor,通过回调Spring自己添加的ConfigurationClassPostProcessor以及用户添加的bean工厂的后置处理器,完成了包扫描以及对主配置类代理的工作
本篇博文将继续往下跟进
程序入口:注册bean的后置处理器
AbstractApplicationContext的registerBeanPostProcessors(beanFactory);方法
通过方法名字,见名知意, 注册bean的后置处理器, 说白了就是将系统中所有的bean的后置处理器统一交给Spring的beanFactory管理
那么问题来了
什么是BeanPostProcessor? 有什么作用?
Bean的后置处理器,首先来说,他是Spring中抽象出来的一个顶级的接口, 他里面有如下有如下两个方法, 这两个方法的执行时机通过方法的名字也能猜的出, 一个是在构造方法之后,init()方法之前,第二个是在init()方法之后执行
public interface BeanPostProcessor {
@Nullable
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
@Nullable
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
}
public interface BeanPostProcessor {
@Nullable
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
@Nullable
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
}大家说它是Spring对外提供的拓展点,也许是因为,通过实现这个接口,
程序员可以被Spring管理的bean的生命周期进行插手
这也体现了AOP的设计思想,就比如在init()方法执行前后做出不同的动作,其实就是对bean的一种增强
此外BeanPostProcessor可以存在多个,他们会被存储在一个列表中,然后依次被执行
为什么要注册BeanPostProcessor?
所谓的注册,只不过是对当前上下文中所有的BeanPostProcessor进行一种集中式管理罢了, 为什么非得这么做呢? 因为上下文中BeanPostProcessor的数量不是一成不变的,Spring为了启动的正常,需要添加原生的BeanPostProcessor,程序员因为自己的需求也会添加不同数量的bean的后置处理器,因此需要这种策略,将上下文中所有的后置处理器进行统一的管理,方便回调
源码阅读:
这段代码的逻辑很清楚简明: 首先,根据类型从当前的上面中取出所有的BeanPostProcessor的实现类,那么问题来了,当前上下文中有几个呢?如下图:
这三个中的前两个后置还处理器是在prepareBeanFactory()时添加进去的,第三个是在为主配置类生成代理时传递进去的
紧接着调用beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false),结果如下图
前三个处理器是不是很熟悉? 没错,他们是创建AnnotationedBeanDefinitionReader时创建的6个RootBeanDefinition中 的第4-5-6个, 其中的AutowiredAnnotationBeanPostProcessor的主要功能是处理@Autowired注解,并且解决了setter方式的循环依赖问题, CommonAnnotationBeanPostProcessor 主要处理@Resource @PostConstructor @PreDestory注解RequiredAnnotationBeanPostProcessor处理@Required注解, 上图中的最后一个注解是``
在下面的代码中,Spring开始根据不同的处理器的注解标注情况,接口的实现情况进行排序处理, 并且又添加了两个后置处理器
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
// 根据类型从beanFactory中取出所有实现BeanPostProcessor接口的实现类的名字
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
// 这是个内部类,用来检查是否在bean的创建过程中,经过了所有本来应经过的后置处理器
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
// 将添加执行注解,实现排序接口的beanPostProcessor添加到相应的集合中
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// 按照优先顺序排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 批量注册priorityOrderedPostProcessors中的bean的后置处理器
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String ppName : orderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
orderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 再次排序,注册
sortPostProcessors(orderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
// Now, register all regular BeanPostProcessors.
// todo 现在注册 全部 正常的没有排序的BeanPostProcessor
List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String ppName : nonOrderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
nonOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 再次排序,注册
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
sortPostProcessors(internalPostProcessors, beanFactory);
// Finally, re-register all internal BeanPostProcessors.
// 最后注册所有内置的BeanPostProcessor
registerBeanPostProcessors(beanFactory, internalPostProcessors);
//这里又添加了一个处理器
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
// 根据类型从beanFactory中取出所有实现BeanPostProcessor接口的实现类的名字
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
// 这是个内部类,用来检查是否在bean的创建过程中,经过了所有本来应经过的后置处理器
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
// 将添加执行注解,实现排序接口的beanPostProcessor添加到相应的集合中
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// 按照优先顺序排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 批量注册priorityOrderedPostProcessors中的bean的后置处理器
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String ppName : orderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
orderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 再次排序,注册
sortPostProcessors(orderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
// Now, register all regular BeanPostProcessors.
// todo 现在注册 全部 正常的没有排序的BeanPostProcessor
List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String ppName : nonOrderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
nonOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 再次排序,注册
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
sortPostProcessors(internalPostProcessors, beanFactory);
// Finally, re-register all internal BeanPostProcessors.
// 最后注册所有内置的BeanPostProcessor
registerBeanPostProcessors(beanFactory, internalPostProcessors);
//这里又添加了一个处理器
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}beanPostProcessor全部注册到了AbstractBeanFactory中的下面这个字段中
private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();
private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();
