接口简介
BeanFactoryPostProcessor 接口是 Spring 初始化 BeanFactory 时对外暴露的扩展点,Spring IoC 容器允许 BeanFactoryPostProcessor 在容器实例化任何 bean 之前读取 bean 的定义,并可以修改它。
BeanDefinitionRegistryPostProcessor 继承自 BeanFactoryPostProcessor,比 BeanFactoryPostProcessor 具有更高的优先级,主要用来在常规的 BeanFactoryPostProcessor 检测开始之前注册其他 bean 定义。特别是,你可以通过 BeanDefinitionRegistryPostProcessor 来注册一些常规的 BeanFactoryPostProcessor,因为此时所有常规的 BeanFactoryPostProcessor 都还没开始被处理。
注意点:通过BeanDefinitionRegistryPostProcessor 注册的 BeanDefinitionRegistryPostProcessor 接口的postProcessBeanDefinitionRegistry方法将得不到调用,具体的原因会在下面的代码中解释。
BeanFactoryPostProcessor 接口调用机制
BeanFactoryPostProcessor 接口的调用在 AbstractApplicationContext#invokeBeanFactoryPostProcessors方法中。
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
进入PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors())方法:
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// 用于存放已经处理过的Bean名字
Set<String> processedBeans = new HashSet<>();
// 一般会进入这个判断
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
// 所谓的regularPostProcessors就是指实现BeanFactoryPostProcessor接口的Bean
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
// 所谓的registryProcessors就是指实现BeanDefinitionRegistryPostProcessor接口的Bean
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
// 这边遍历的是通过ApplicationContext接口注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor接口
// 需要和BeanFactory中BeanDefinitionMap中的BeanFactoryPostProcessor接口区分开
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
//如果是BeanDefinitionRegistryPostProcessor,则先进行postProcessBeanDefinitionRegistry处理,这个方法一般进行BeanDefinition注册,从这边可以看出BeanDefinitionRegistryPostProcessor接口的方法先调用,所以优先级高于BeanFactoryPostProcessor
// 通过这个代码可以看出,通过ApplicationContext直接注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor并不支持Order接口,而是根据注册的顺序执行
registryProcessor.postProcessBeanDefinitionRegistry(registry);
// 保存这个BeanDefinitionRegistryPostProcessor,因为还要执行这个类的BeanFactoryPostProcessor方法;
registryProcessors.add(registryProcessor);
}
else {
// 保存,后面还要执行这个类的BeanFactoryPostProcessor方法;
regularPostProcessors.add(postProcessor);
}
}
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// 这边获取的是BeanFactory中的BeanDefinitionRegistryPostProcessor
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
//先处理PriorityOrdered标注的BeanDefinitionRegistryPostProcessor
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
//将其标记为已经处理,防止重复处理
processedBeans.add(ppName);
}
}
// 将其排序,以便按顺序处理
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 将其保存,以便处理这个类的BeanFactoryPostProcessor方法
registryProcessors.addAll(currentRegistryProcessors);
// 执行BeanDefinitionRegistryPostProcessor接口方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
// 清除,以便开始处理@Order标注的注解
currentRegistryProcessors.clear();
// 注意:这边重新获取BeanDefinitionRegistryPostProcessor是有深意的,因为上面在处理@PriorityOrdered标注的BeanDefinitionRegistryPostProcessor时可能又注入了新的BeanDefinitionRegistryPostProcessor。
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 判断是否处理过,防止重复处理,下面的逻辑和上面相同, 不介绍了
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// 处理不标注注解的BeanDefinitionRegistryPostProcessor
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
}
// 调用postProcessBeanFactory 方法,所以BeanDefinitionRegistryPostProcessor中的postProcessBeanFactory方法的优先级要高。
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// 开始处理BeanFactoryPostProcessor接口
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// 也是按照@PriorityOrdered @Ordered 和普通的方式进行处理
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
// 可能已经处理过
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// 先执行@PriorityOrdered标注的接口
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 处理@Order标注的类
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {
// 这边通过名字重新拿了Bean,应该是怕上面的处理改变了Bean
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// 最后调用普通的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
beanFactory.clearMetadataCache();
}
简单总结
上面的方法看起来很长很复杂,但其实干的事情并不多,就调用了BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor接口的实现。这边再简单总结下具体的过程:
step1:执行通过ApplicationContext#addBeanFactoryPostProcessor()方法注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor。
具体过程如下:假如通过ApplicationContext注册了一个BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor,那么会先执行BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法,但是BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法和BeanFactoryPostProcessor的postProcessBeanFactory方法暂时都不会在这步执行。
另外需要注意的是:通过ApplicationContext注册的BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor都不支持@PriorityOrdered和@Ordered顺序处理,而是按照我们添加的顺序处理
step2:处理BeanFactory中的BeanDefinitionRegistryPostProcessor,处理的顺序是先处理@PriorityOrdered标注的,再处理@Ordered标注的,最后处理普通的BeanDefinitionRegistryPostProcessor。到这边,所有BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry方法都已经调用完毕,下面就开始处理BeanFactoryPostProcessor的postProcessBeanFactory方法。
step3:调用BeanDefinitionRegistryPostProcessor实现的postProcessBeanFactory方法(因为BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口)
step4:调用通过ApplicationContext#addBeanFactoryPostProcessor()注册的“单纯”的BeanFactoryPostProcessor
step5:调用BeanFactory中的BeanFactoryPostProcessor,调用顺序也是按照@PriorityOrdered和@Ordered顺序处理,没有这两个注解的最后处理。
好了,到这边BeanFactoryPostProcessor和BeanDefinitionRegistryPostProcessor接口就已经处理完了。后面我们会拿ConfigurationClassPostProcessor 这个特殊的BeanDefinitionRegistryPostProcessor做列子讲下具体流程,这边只是介绍BeanFactoryPostProcessor的调用机制。