Spring Framework版本 5.3.4
1. BeanPostProcessor是干什么的？
BeanPostProcessor接口作用是：如果咱们须要在Spring容器实现Bean的实例化、配置和其余的初始化前后增加一些本人的逻辑解决，咱们就能够定义一个或者多个BeanPostProcessor接口的实现，而后注册到容器中。(相似于拦截器和过滤器)。 BeanPostProcessor分为三大类如下图：
- 实例化
- 初始化
- 销毁
Bean实例化会执行 InstantiationAwareBeanPostProcessor 、 SmartInstantiationAwareBeanPostProcessor 这两类处理器，Bean实例化后每个bean就会通过 BeanPostProcessor 、 MergedBeanDefinitionPostProcessor 实现的类的解决。Bean销毁会通过 DestructionAwareBeanPostProcessor 处理器。
Spring Bean的实例化图解：
在查看完 Aware 接口后，就开始调用 BeanPostProcessor 进行前置解决后置解决。上面来看一下Spring中的几类继承：
- AOP相干的
- bean 和 context相干的
- Spring Boot相干的实现
BeanPostProcessor是在Bean实例化后，在自定义初始化办法前后执行。
2. BeanPostProcessor
处理器定义了Bean 初始化 前后执行的办法。
public interface BeanPostProcessor { //自定义初始化办法之前执行 @Nullable default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { return bean; } //自定义初始化办法之后执行 @Nullable default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { return bean; }}代码示例地址：github.com/mxsm/spring…
代码演示：
public class MyBeanPostProcessor implements BeanPostProcessor { @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { System.out.println( " ----before----- " + beanName); return bean; } @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println( " ----after----- " + beanName); return bean; }}public class TestBean { private String name; public void init(){ System.out.println("TestBean---init()"); this.name = "test"; } public String getName() { return name; } public void setName(String name) { this.name = name; }}<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd"> <bean id="testBean" class="com.github.mxsm.bean.TestBean" init-method="init"/> <bean class="com.github.mxsm.processor.MyBeanPostProcessor" id="myBeanPostProcessor"/></beans>public class ApplicationBoot{ public static void main( String[] args ) { ApplicationContext applicationContext = new ClassPathXmlApplicationContext("application.xml"); TestBean testBean = applicationContext.getBean(TestBean.class); System.out.println(testBean.getName()); }}
通过代码能够看进去执行的后果。
3.InstantiationAwareBeanPostProcessor
该处理器定义了Bean 实例化 前后执行的办法。
public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor { //实例化之前 @Nullable default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException { //这里能够自定义代理类 return null; } //实例化后-然而执行在初始化之前 default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException { return true; } //解决bean的Properties值 @Nullable default PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException { return null; }}4.DestructionAwareBeanPostProcessor
该处理器了销毁Bean之前的操作。
public interface DestructionAwareBeanPostProcessor extends BeanPostProcessor { //bean销毁之前 void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException; //bean是否须要销毁 default boolean requiresDestruction(Object bean) { return true; }}5. 看一下Spring本身的实现
class ApplicationContextAwareProcessor implements BeanPostProcessor { private final ConfigurableApplicationContext applicationContext; private final StringValueResolver embeddedValueResolver; /** * Create a new ApplicationContextAwareProcessor for the given context. */ public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) { this.applicationContext = applicationContext; this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory()); } @Override @Nullable public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException { AccessControlContext acc = null; if (System.getSecurityManager() != null && (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware || bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware || bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) { acc = this.applicationContext.getBeanFactory().getAccessControlContext(); } if (acc != null) { AccessController.doPrivileged((PrivilegedAction<Object>) () -> { invokeAwareInterfaces(bean); return null; }, acc); } else { invokeAwareInterfaces(bean); } return bean; } private void invokeAwareInterfaces(Object bean) { if (bean instanceof Aware) { if (bean instanceof EnvironmentAware) { ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment()); } if (bean instanceof EmbeddedValueResolverAware) { ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver); } if (bean instanceof ResourceLoaderAware) { ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext); } if (bean instanceof ApplicationEventPublisherAware) { ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext); } if (bean instanceof MessageSourceAware) { ((MessageSourceAware) bean).setMessageSource(this.applicationContext); } if (bean instanceof ApplicationContextAware) { ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext); } } } @Override public Object postProcessAfterInitialization(Object bean, String beanName) { return bean; }}以后次要用来解决继承了 Aware 接口类。而后依据 Aware 接口的不同实现设置对应的接口对象
6. BeanPostProcessor Spring源码剖析
首先明确一点 BeanPostProcessor 实现的类都是Spring容器中的一个Bean。在 AbstractApplicationContext#refresh 是最重要的一个办法：
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { //省了局部代码 try { //省了局部代码 // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); //省了局部代码 } catch (BeansException ex) { } finally { //省了局部代码 } }}protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) { //通过PostProcessorRegistrationDelegate类的静态方法解决 PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);}上面看一下 PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this); 办法
public static void registerBeanPostProcessors( ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) { String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false); // Register BeanPostProcessorChecker that logs an info message when // a bean is created during BeanPostProcessor instantiation, i.e. when // a bean is not eligible for getting processed by all BeanPostProcessors. int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length; beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount)); //解决分为三类：1 PriorityOrdered实现 2 Ordered 第三类就是一般的 List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>(); List<BeanPostProcessor> internalPostProcessors = new ArrayList<>(); List<String> orderedPostProcessorNames = new ArrayList<>(); List<String> nonOrderedPostProcessorNames = new ArrayList<>(); 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); } } // 解决PriorityOrdered实现 sortPostProcessors(priorityOrderedPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors); // 解决 Ordered实现. 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); } } sortPostProcessors(orderedPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, orderedPostProcessors); // 解决失常的 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); } } registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors); //注册MergedBeanDefinitionPostProcessor sortPostProcessors(internalPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, internalPostProcessors); // Re-register post-processor for detecting inner beans as ApplicationListeners, // moving it to the end of the processor chain (for picking up proxies etc). beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext)); }通过该办法将 BeanPostProcessor 的以上几种实现类都注册到Spring中。
而后在生成Bean的时候去执行， AbstractAutowireCapableBeanFactory.createBean 创立Bean
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException { //省略代码 try { // 执行实例化之前办法. Object bean = resolveBeforeInstantiation(beanName, mbdToUse); if (bean != null) { return bean; } //省略代码 } } protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) { Object bean = null; if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) { if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { Class<?> targetType = determineTargetType(beanName, mbd); if (targetType != null) { //执行InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation(实例化之前办法) bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName); if (bean != null) { //执行InstantiationAwareBeanPostProcessor#postProcessAfterInitialization(初始化后的办法) bean = applyBeanPostProcessorsAfterInitialization(bean, beanName); } } } mbd.beforeInstantiationResolved = (bean != null); } return bean; }通过代码能够晓得 resolveBeforeInstantiation 办法是执行实例化之前的办法。如果实例化之前的办法返回了对应Bean那么间接执行初始化后的办法。实例化 InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation 办法执行返回Bean为空就调用 AbstractAutowireCapableBeanFactory#doCreateBean 办法。在这个办法外面有如下几个重要的办法：
- AbstractAutowireCapableBeanFactory#applyMergedBeanDefinitionPostProcessors 办法
- 执行 MergedBeanDefinitionPostProcessor#postProcessMergedBeanDefinition 办法
- AbstractAutowireCapableBeanFactory#populateBean 办法
- 执行 InstantiationAwareBeanPostProcessor#postProcessAfterInstantiation 办法，如果后面办法返回true，执行办法 InstantiationAwareBeanPostProcessor#postProcessProperties 办法
- AbstractAutowireCapableBeanFactory#initializeBean 办法
- 执行 BeanPostProcessor#postProcessBeforeInitialization 办法，而后执行 AbstractAutowireCapableBeanFactory#invokeInitMethods 办法(包含实现了InitializingBean接口的办法或者有注解@PostConstruct的办法)，而后执行 BeanPostProcessor#postProcessAfterInitialization
7. 总结
BeanPostProcessor 次要用来解决Bean外部的注解。比方Spring本人实现的@Autowired、@Value， @EJB，@WebServiceRef，@PostConstruct，@PreDestroy等
自定义相似于@Value，@Autowired的注解，次要用于Java类变量或者办法上的注解 次要用于解决Bean外部的注解实现，次要是变量或者办法下面的注解