1.BeanPostProcessor原理

先說，bean的后置處理器BeanPostProcessor接口中兩個方法：

• postProcessBeforeInitialization:在初始化之前工作
• postProcessAfterInitialization:在初始化之后工作

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BeanPostProcessor原理

• populateBean(beanName, mbd, instanceWrapper);//給bean進行屬性賦值
• 調用initializeBean方法，執行后置處理器和指定的初始化方法。（詳細過程見下面源碼）
• 后置處理器BeanPostProcessor執行過程是，遍歷得到容器中所有的BeanPostProcessor；挨個執行beforeInitialization，一但返回null，跳出for循環，不會執行后面的BeanPostProcessor.postProcessorsBeforeInitialization

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核心執行方法initializeBean：

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean

initializeBean

{

applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);

invokeInitMethods(beanName, wrappedBean, mbd);執行自定義初始化

applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);

}

/*** Initialize the given bean instance, applying factory callbacks* as well as init methods and bean post processors.* <p>Called from {@link #createBean} for traditionally defined beans,* and from {@link #initializeBean} for existing bean instances.* @param beanName the bean name in the factory (for debugging purposes)* @param bean the new bean instance we may need to initialize* @param mbd the bean definition that the bean was created with* (can also be {@code null}, if given an existing bean instance)* @return the initialized bean instance (potentially wrapped)* @see BeanNameAware* @see BeanClassLoaderAware* @see BeanFactoryAware* @see #applyBeanPostProcessorsBeforeInitialization* @see #invokeInitMethods* @see #applyBeanPostProcessorsAfterInitialization*/protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {if (System.getSecurityManager() != null) {AccessController.doPrivileged((PrivilegedAction<Object>) () -> {invokeAwareMethods(beanName, bean);return null;}, getAccessControlContext());}else {//調用實現XXAware接口的方法invokeAwareMethods(beanName, bean);}Object wrappedBean = bean;if (mbd == null || !mbd.isSynthetic()) {//后置處理器--前置方法wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);}try {//調用@bean或者<bean>標簽中指定的初始化方法invokeInitMethods(beanName, wrappedBean, mbd);}catch (Throwable ex) {throw new BeanCreationException((mbd != null ? mbd.getResourceDescription() : null),beanName, "Invocation of init method failed", ex);}if (mbd == null || !mbd.isSynthetic()) {//后置處理器--后置方法wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);}return wrappedBean;}//后置處理器--前置方法@Overridepublic Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)throws BeansException {Object result = existingBean;for (BeanPostProcessor processor : getBeanPostProcessors()) {Object current = processor.postProcessBeforeInitialization(result, beanName);if (current == null) {return result;}result = current;}return result;}//后置處理器--后置方法 處理方式都是會遍歷所有的后置處理器，調用前置或后置方法@Overridepublic Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)throws BeansException {Object result = existingBean;for (BeanPostProcessor processor : getBeanPostProcessors()) {Object current = processor.postProcessAfterInitialization(result, beanName);if (current == null) {return result;}result = current;}return result;}

2.BeanPostProcessor 后置處理器在Spring底層中有那些應用

Spring底層對 BeanPostProcessor 的使用；

bean賦值，注入其他組件，@Autowired，生命周期注解功能，@Async,xxx BeanPostProcessor;

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3.BeanPostProcessor 使用

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public class BeanLife {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "BeanLife{" +"name='" + name + '\'' +'}';}public BeanLife() {System.out.println("構造方法：BeanLife--->construct...");}}/*** @author tuchuanbiao* @Date 2019/4/3 19:58** 后置處理器：初始化前后進行處理工作* 將后置處理器加入到容器中** 這里采用@Bean方式注入，也可以直接使用@Component*/ //@Component //一定要將后置處理器注入到容器中 public class MyBeanPostProcessor implements BeanPostProcessor {@Nullable@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.println("bean后置處理器：MyBeanPostProcessor......postProcessBeforeInitialization");return bean;}@Nullable@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.println("bean后置處理器：MyBeanPostProcessor......postProcessAfterInitialization");return bean;} }@Configuration public class BeanLifeCycleConfig {@Bean(value = "beanLife")public BeanLife life() {BeanLife beanLife = new BeanLife();beanLife.setName("張三");System.out.println(beanLife);return beanLife;}@Beanpublic MyBeanPostProcessor myBeanPostProcessor(){return new MyBeanPostProcessor();} }//測試類public class BeanLifeCycleTest {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanLifeCycleConfig.class);System.out.println("applicationContext ..... 初始化結束");System.out.println("applicationContext ..... 準備關閉");applicationContext.close();System.out.println("applicationContext ..... 已關閉");}}運行結果： 構造方法：BeanLife--->construct... BeanLife{name='張三'} bean后置處理器：MyBeanPostProcessor......postProcessBeforeInitialization bean后置處理器：MyBeanPostProcessor......postProcessAfterInitialization applicationContext ..... 初始化結束 applicationContext ..... 準備關閉 applicationContext ..... 已關閉

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