认识Spring中的BeanFactoryPostProcessor
认识Spring中的BeanFactoryPostProcessor
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发布于 2024-06-11 08:26:33
发布于 2024-06-11 08:26:33
文章被收录于专栏：Java技术进阶
先看下AI的介绍
在Spring 5.3.x中，BeanFactoryPostProcessor是一个重要的接口，用于在Spring IoC容器实例化任何bean之前，读取bean的定义（配置元数据），并可能对其进行修改。以下是关于BeanFactoryPostProcessor的详细介绍：
1. 接口定义与功能
接口定义：BeanFactoryPostProcessor是Spring提供的一个接口，它允许用户自定义逻辑以修改或扩展容器内部的功能。
功能：在BeanFactory实例化之后、其他Bean被创建之前，执行一些自定义的修改或增强操作。这包括修改BeanDefinition（bean的定义信息），如修改属性、添加或删除bean等。
2. 使用方法
实现接口：要使用BeanFactoryPostProcessor，你需要创建一个类来实现这个接口，并重写其中的postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)方法。
注册：将你的BeanFactoryPostProcessor实现注册为Spring容器中的一个bean。这通常可以通过XML配置文件、Java配置类或注解（如@Bean）来完成。
3. 子接口BeanDefinitionRegistryPostProcessor
定义：BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的一个子接口，它添加了一个额外的方法postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)。
功能：除了可以修改BeanDefinition之外，它还可以注册新的bean定义到容器中。
4. 执行顺序
如果有多个BeanFactoryPostProcessor或BeanDefinitionRegistryPostProcessor，可以通过设置order属性或实现Ordered接口来定义它们的执行顺序。
5. 示例
示例代码可能包括一个实现BeanFactoryPostProcessor接口的类，以及一个将其注册为Spring bean的配置类或注解。这个类中的postProcessBeanFactory方法会包含自定义的修改或增强逻辑。
6. 与其他接口的区别
BeanFactoryPostProcessor和BeanPostProcessor都是Spring初始化bean时对外暴露的扩展点，但它们的作用和使用场景不同。BeanFactoryPostProcessor主要关注于修改或增强BeanFactory和BeanDefinition，而BeanPostProcessor则关注于Bean实例化前后的操作。
7. 总结
BeanFactoryPostProcessor是Spring框架中一个非常有用的接口，它允许你在Spring IoC容器实例化bean之前，对bean的定义进行自定义的修改或增强。通过实现这个接口并注册你的实现类，你可以扩展Spring容器的功能，满足更复杂的应用需求。根据BeanFactoryPostProcessor的介绍，创建几个测试类： A类 通过扫描增加，BeanFactoryPostProcessor 实现类
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;
/**
* 简单实现
*/
@Component
public class A implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("A scan");
}
}B类 通过扫描增加，实现BeanFactoryPostProcessor, PriorityOrdered类
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;
@Component
public class B implements BeanFactoryPostProcessor, PriorityOrdered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("B scan, priorityOrdered 0");
}
@Override
public int getOrder() {
return 0;
}
}B1类 通过扫描增加，实现BeanFactoryPostProcessor, PriorityOrdered类，排序靠后
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;
@Component
public class B1 implements BeanFactoryPostProcessor, PriorityOrdered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("B1 scan, priorityOrdered 1");
}
@Override
public int getOrder() {
return 1;
}
}C类 通过扫描增加，实现BeanFactoryPostProcessor, Ordered 类
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.core.Ordered;
import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;
@Component
public class C implements BeanFactoryPostProcessor, Ordered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("C scan, Ordered 0");
}
@Override
public int getOrder() {
return 0;
}
}C1类 通过扫描增加，实现BeanFactoryPostProcessor, Ordered 类，排序靠后
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.core.Ordered;
import org.springframework.stereotype.Component;
@Component
public class C1 implements BeanFactoryPostProcessor, Ordered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("C1 scan, Ordered 1");
}
@Override
public int getOrder() {
return 1;
}
}D类 通过扫描增加，实现BeanFactoryPostProcessor的类，注解@Order
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
@Component
@Order(1)
public class D implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("D scan, @Ordered 1");
}
}E类 在测试类中，通过api增加
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
public class E implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("E parent api add");
}
}F类 普通Bean
package org.springframework.example.BFPP;
import org.springframework.stereotype.Component;
@Component
public class F {
private String name;
@Override
public String toString() {
return "F{" +
"name='" + name + '\'' +
'}';
}
}F1类 修改的Bean
package org.springframework.example.BFPP;
import org.springframework.stereotype.Component;
@Component
public class F1 {
private String name;
@Override
public String toString() {
return "F1{" +
"name='" + name + '\'' +
'}';
}
}G类 其中修改了F的BeanDefinition
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.stereotype.Component;
@Component
public class G implements BeanFactoryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
AbstractBeanDefinition beanDefinition = (AbstractBeanDefinition) beanFactory.getBeanDefinition("f");
beanDefinition.setBeanClass (F1.class);
}
}H类 扫描增加，实现了BeanDefinitionRegistryPostProcessor 的类
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.stereotype.Component;
@Component
public class H implements BeanDefinitionRegistryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("H sub-parent");
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
System.out.println("H sub");
}
}I类 在J类中增加，实现了BeanDefinitionRegistryPostProcessor 的类
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.stereotype.Component;
public class I implements BeanDefinitionRegistryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("I sub-parent");
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
System.out.println("I sub");
}
}J类 通过扫描增加，实现了BeanDefinitionRegistryPostProcessor 的类
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.stereotype.Component;
@Component
public class J implements BeanDefinitionRegistryPostProcessor {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("J sub-parent");
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
System.out.println("J sub add BFPP I");
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(I.class);
registry.registerBeanDefinition("i", builder.getBeanDefinition());
}
}K类 通过扫描增加，实现了BeanDefinitionRegistryPostProcessor 、PriorityOrdered 的类
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;
@Component
public class K implements BeanDefinitionRegistryPostProcessor, PriorityOrdered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("k sub-parent priorityOrdered 0");
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
System.out.println("K sub priorityOrdered 0");
}
@Override
public int getOrder() {
return 0;
}
}K1类 通过扫描增加，实现了BeanDefinitionRegistryPostProcessor 、PriorityOrdered 的类，排序靠后
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;
@Component
public class K1 implements BeanDefinitionRegistryPostProcessor, PriorityOrdered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("k1 sub-parent priorityOrdered 1");
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
System.out.println("K1 sub priorityOrdered 1");
}
@Override
public int getOrder() {
return 1;
}
}L类 通过扫描增加，实现了BeanDefinitionRegistryPostProcessor 、Ordered 的类
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.core.Ordered;
import org.springframework.core.PriorityOrdered;
import org.springframework.stereotype.Component;
@Component
public class L implements BeanDefinitionRegistryPostProcessor, Ordered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("L sub-parent Ordered 0");
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
System.out.println("L sub Ordered 0");
}
@Override
public int getOrder() {
return 0;
}
}L1类 通过扫描增加，实现了BeanDefinitionRegistryPostProcessor 、Ordered 的类，排序靠后
package org.springframework.example.BFPP;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.core.Ordered;
import org.springframework.stereotype.Component;
@Component
public class L1 implements BeanDefinitionRegistryPostProcessor, Ordered {
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
System.out.println("L1 sub-parent Ordered 1");
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
System.out.println("L1 sub Ordered 1");
}
@Override
public int getOrder() {
return 1;
}
}BFPPTest测试类
package org.springframework.example.BFPP;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class BFPPTest {
public static void main(String[] args) {
AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext();
annotationConfigApplicationContext.scan("org.springframework.example.BFPP");
annotationConfigApplicationContext.addBeanFactoryPostProcessor(new E());
annotationConfigApplicationContext.addBeanFactoryPostProcessor(new E1());
annotationConfigApplicationContext.refresh();
System.out.println(annotationConfigApplicationContext.getBean("f"));
}
}运行结果
E1 sub api add
K sub priorityOrdered 0
K1 sub priorityOrdered 1
L sub Ordered 0
L1 sub Ordered 1
H sub
J sub add BFPP I
I sub
E1 sub parent api add
k sub-parent priorityOrdered 0
k1 sub-parent priorityOrdered 1
L sub-parent Ordered 0
L1 sub-parent Ordered 1
H sub-parent
J sub-parent
I sub-parent
E parent api add
B scan, priorityOrdered 0
B1 scan, priorityOrdered 1
C scan, Ordered 0
C1 scan, Ordered 1
A scan
D scan, @Ordered 1
F1{name='null'}可以看到执行顺序是： 1、执行实现了BeanDefinitionRegistryPostProcessor接口，通过addBeanFactoryPostProcessor 添加的类 2、执行实现了BeanDefinitionRegistryPostProcessor接口、PriorityOrdered接口的类 3、执行实现了BeanDefinitionRegistryPostProcessor接口、Ordered 接口的类 4、执行剩余实现了BeanDefinitionRegistryPostProcessor接口的类，以及后置处理中新增的BeanDefinitionRegistryPostProcessor类 5、执行实现了BeanDefinitionRegistryPostProcessor接口类的父类BeanFactoryPostProcessor的postProcessBeanFactory方法 6、执行实现了父类BeanFactoryPostProcessor接口，通过addBeanFactoryPostProcessor 添加的类 7、执行实现了父类BeanFactoryPostProcessor接口、PriorityOrdered接口的类 8、执行实现了父类BeanFactoryPostProcessor接口、Ordered 接口的类 9、其他剩余实现了BeanFactoryPostProcessor接口的类
接着来分析一下源码： BeanFactoryPostProcessor的处理也是在AbstractApplicationContext的refresh内invokeBeanFactoryPostProcessors中，继续跟踪直到PostProcessorRegistrationDelegate–>invokeBeanFactoryPostProcessors。
发现没有，跟前面的BeanPostProcessor的处理在同一个类中
/**
* 调用BeanFactory 后置处理器
* @param beanFactory
* @param beanFactoryPostProcessors
*/
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// WARNING: Although it may appear that the body of this method can be easily
// refactored to avoid the use of multiple loops and multiple lists, the use
// of multiple lists and multiple passes over the names of processors is
// intentional. We must ensure that we honor the contracts for PriorityOrdered
// and Ordered processors. Specifically, we must NOT cause processors to be
// instantiated (via getBean() invocations) or registered in the ApplicationContext
// in the wrong order.
//
// Before submitting a pull request (PR) to change this method, please review the
// list of all declined PRs involving changes to PostProcessorRegistrationDelegate
// to ensure that your proposal does not result in a breaking change:
// https://github.com/spring-projects/spring-framework/issues?q=PostProcessorRegistrationDelegate+is%3Aclosed+label%3A%22status%3A+declined%22
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
//存放所有已经处理的Bean名称，避免重复处理
Set<String> processedBeans = new HashSet<>();
//先处理beanFactory是BeanDefinitionRegistry类型的，BeanDefinitionRegistry 用来注册和管理BeanDefinition
//在spring中一般都是DefaultListableBeanFactory
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
//存放常规的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
//存放BeanDefinitionRegistryPostProcessor类型的BeanFactoryPostProcessor
//其是BeanFactoryPostProcessor的子类
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
//先处理BeanDefinitionRegistryPostProcessor类型的BeanFactoryPostProcessor
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
//处理常规的BeanFactoryPostProcessor
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.
//存放当前执行的BeanDefinitionRegistryPostProcessor
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
//获取BeanDefinitionRegistryPostProcessor类型的BeanFactoryPostProcessor 名称
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
//处理实现了PriorityOrdered接口的BeanDefinitionRegistryPostProcessor
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
//排序
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
//里面循环调用BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
//清空当前执行的BeanDefinitionRegistryPostProcessor列表，因为后面还要用
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
//处理实现了Ordered接口的BeanDefinitionRegistryPostProcessor
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
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, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
//最后处理其他的BeanDefinitionRegistryPostProcessor，直到没有新的BeanDefinitionRegistryPostProcessor
//循环处理，因为在BeanDefinitionRegistryPostProcessor中可能会注册新的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, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
//调用所有已处理的BeanDefinitionRegistryPostProcessors和BeanFactoryPostProcessors的postProcessBeanFactory方法
//这段内部调用的是BeanDefinitionRegistryPostProcessor父类的postProcessBeanFactory方法
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
//如果beanFactory不是一个BeanDefinitionRegistry，直接调用所有的bean工厂后处理器
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!
//查找所有实现了父类BeanFactoryPostProcessor接口的bean
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
//存放priorityOrdered的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
//存放ordered的BeanFactoryPostProcessor
List<String> orderedPostProcessorNames = new ArrayList<>();
//存放没有实现priorityOrdered和ordered的BeanFactoryPostProcessor
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
//前面已经处理过了，就跳过
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);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
//处理实现priorityOrdered的BeanFactoryPostProcessor
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
//处理实现ordered的BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
//处理没有实现priorityOrdered和ordered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...
//清空缓存的合并bean定义，因为后处理器可能修改了原始的元数据，例如替换值中的占位符
beanFactory.clearMetadataCache();
}Debug 启动，能够看到beanFactory 是 DefaultListableBeanFactory，所以进入BeanDefinitionRegistry部分，此时的beanFactoryPostProcessors 只有E、E1，这两个是通过BFPPTest类中的addBeanFactoryPostProcessor增加，会在invokeBeanFactoryPostProcessors中最先获取。
继续往下执行，随后会判断postProcessor类型是否是BeanDefinitionRegistryPostProcessor类型，如果是会最先得到处理，调用其postProcessBeanDefinitionRegistry方法。
所以E1类是实现了BeanDefinitionRegistryPostProcessor接口，并且通过api增加，就在这里最先打印日志。
继续执行，来到了处理实现了PriorityOrdered接口的类。
继续执行，下面来处理实现了Ordered接口的类
继续执行到了，循环处理部分，此处会处理在J类中增加的I类。
继续执行，开始处理实现了BeanDefinitionRegistryPostProcessor接口父类的postProcessBeanFactory方法
下一步接口处理通过最开始采集到的regularPostProcessors中的BeanFactoryPostProcessor，此时这个里面只有一个E类，我们通过api接口添加
到这里为止，BeanDefinitionRegistryPostProcessor接口的类已经处理完毕。
接口处理BeanFactoryPostProcessor接口的类，会把实现了BeanDefinitionRegistryPostProcessor接口的类也找出来，因为BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子类
后面是同样的操作，先处理实现了PriorityOrdered接口的类，再处理Ordered的类，最后出来其他类。加了@Order注解的类，是当做没有实现排序类处理，所以加@Order注解对于排序在这里同样是没用的，跟BeanPostProcessor一样。
最后，清除缓存的合并Bean definitions，为什么要清除？好像是在并发环境下会获取到老的Bean。见：https://github.com/spring-projects/spring-framework/issues/18841
至于对BeanDefinition的修改，在G类里面将F对应的Bean类修改为F1，最后从容器中获取的Bean也是确实变成了F1。
本文参与 腾讯云自媒体同步曝光计划，分享自作者个人站点/博客。
原始发表：2024-06-10，如有侵权请联系 cloudcommunity@tencent.com 删除
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