示例
public class PrintBeanFactoryPostProcessor implements BeanFactoryPostProcessor{
public PrintBeanFactoryPostProcessor() {
System.out.println("实例化PrintBeanFactoryPostProcessor");
}
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
String[] beanNames = beanFactory.getBeanDefinitionNames();
for (String beanName : beanNames) {
System.out.println("beanName : " +beanName);
}
}
}
<beans:bean id="printBeanFactoryPostProcessor" class="cn.spy.spring.source.code.PrintBeanFactoryPostProcessor"></beans:bean>
public static void main(String[] args) {
ApplicationContext ac = new ClassPathXmlApplicationContext("spring.xml");
}
IOC容器默认执行实现了BeanFactoryPostProcessor接口的类的方法。
后置处理器源码
执行BeanFactory后处理入口
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
}
委派PostProcessorRegistrationDelegate类之invokeBeanFactoryPostProcessors方法实现
// 回调所有BeanFactory的后置处理器
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
Set<String> processedBeans = new HashSet<String>();
// beanFactory为BeanDefinitionRegistry类型，进行处理
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
new LinkedList<BeanDefinitionRegistryPostProcessor>();
// 硬编码注册的后处理器
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
// BeanDefinitionRegistryPostProcessor类型的后置处理器先执行
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryPostProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
registryPostProcessors.add(registryPostProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// Separate between BeanDefinitionRegistryPostProcessors that implement
// PriorityOrdered, Ordered, and the rest.
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
// 缓存实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessors后置处理器和处理器名称
List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
for (String ppName : postProcessorNames) {
// 匹配PriorityOrdered类型
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
OrderComparator.sort(priorityOrderedPostProcessors);
registryPostProcessors.addAll(priorityOrderedPostProcessors);
/**
* 回调实现PriorityOrdered接口的
* BeanDefinitionRegistryPostProcessors后置处理器的
* postProcessBeanDefinitionRegistry方法
*/
invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);
// 缓存实现Ordered接口的BeanDefinitionRegistryPostProcessors后置处理器和处理器名称
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
OrderComparator.sort(orderedPostProcessors);
registryPostProcessors.addAll(orderedPostProcessors);
/**
* 回调实现Ordered接口的
* BeanDefinitionRegistryPostProcessors后置处理器的
* postProcessBeanDefinitionRegistry方法
*/
invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);
// 调用所有其他BeanDefinitionRegistryPostProcessor后置处理器
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class);
registryPostProcessors.add(pp);
processedBeans.add(ppName);
pp.postProcessBeanDefinitionRegistry(registry);
reiterate = true;
}
}
}
// 回调注册BeanDefinitionRegistryPostProcessor类型处理器
invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
// 回调注册BeanFactoryPostProcessor类型处理器
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// 调用了注册上下文实例的后处理beanFactory
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
List<String> orderedPostProcessorNames = new ArrayList<String>();
List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
// 后处理器分类：PriorityOrdered、Ordered、自定义未实现优先级排序的接口的
for (String ppName : postProcessorNames) {
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);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
// 按照优先级进行排序
OrderComparator.sort(priorityOrderedPostProcessors);
// 回调实现PriorityOrdered接口的
// BeanFactoryPostProcessors后置处理器的
// postProcessBeanFactory方法
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
OrderComparator.sort(orderedPostProcessors);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// 最后，回调没有排序、优先级的实现BeanFactoryPostProcessors接口的postProcessBeanFactory方法
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : nonOrderedPostProcessorNames) {
// 实例化后置处理器bean
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
// 回调postProcessBeanFactory方法
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
}
该方法中处理BeanFactoryPostProcessor主要分为BeanDefinitionRegistry类和普通实现的BeanFactoryPostProcessor接口的类。由于spring对于后处理器调用支持按照PriorityOrdered或者Ordered优先级顺序调用。如果我们要保证读取顺序，也需实现PriorityOrdered或者Ordered接口，所以前面的代码大多在将后置处理器进行分类，搜集到不同的List中，然后执行对应的postProcessBeanFactory回调方法。方法最后的代码就是没有优先级排序的普通的后置处理器，则遍历nonOrderedPostProcessorNames名称集合，通过BeanFactory进行实例化后置处理器bean（getBean方法实现）。然后再回调下postProcessBeanFactory方法。
解释：示例中PrintBeanFactoryPostProcessor （后置处理器bean），会先实例化，所以执行构造方法，打印构造器内容。然后回调postProcessBeanFactory方法，才会打印bean名称。
BeanPostProcessor和BeanFactoryPostProcessor区别
BeanPostProcessor是bean初始化前后回调的接口。
BeanPostProcessor接口
postProcessBeforeInitialization方法：bean初始化之前回调的方法。
postProcessAfterInitialization方法：bean初始化之后回调的方法。
BeanFactoryPostProcessor是beanFactory初始化后回调的接口。
BeanFactoryPostProcessor接口
postProcessBeanFactory方法：beanFactory初始化后回调的方法。
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