Factory hook that allows for custom modification of new bean instances,e.g. checking for marker interfaces or wrapping them with proxies.
允許自定義修改的新的對象實例的工廠鉤子，檢查標記性接口或者包裝成一個代理對象。
ApplicationContexts can autodetect BeanPostProcessor beans in their bean definitions and apply them to any beans subsequently created. Plain bean factories allow for programmatic registration of post-processors,applying to all beans created through this factory.
ApplicationContexts可以在bean定義中自動檢測BeanPostProcessor的beans并且將它們應用與隨后創建的實例類中。 純bean實例工廠允許后處理器的編程注冊，適用于通過該工廠創建的所有bean實例。
Typically, post-processors that populate beans via marker interfaces or the like will implement {@link #postProcessBeforeInitialization}, while post-processors that wrap beans with proxies will normallyimplement {@link #postProcessAfterInitialization}.
通常，通過標記接口等填充bean的后處理器將實現{@link #postProcessBeforeInitialization方法}，而用代理機構包裝bean的后處理器通常會補充{@link #postProcessAfterInitialization方法}。
定義一個實體類：
public class Car {
private ApplicationContext applicationContext;
@Autowired
public void setApplication(ApplicationContext applicationContext) {
System.out.println("=========set=========");
this.applicationContext = applicationContext;
}
public void show(){
System.out.println("================show=========="+applicationContext.getClass());
}
public void init(){
System.out.println("===== Car init ==========");
}
}
@Configuration
public class MyConfig {
@Bean(initMethod="init")
public Car createCar(){
return new Car();
}
}
@Component
public class EchoBeanPostProcessor implements BeanPostProcessor{
/**
* 是在bean依賴裝配（屬性設置完）完成之后觸發
* 這里可以對指定的bean做一些處理，比如說，返該對象的代理對象
*/
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("=========postProcessBeforeInitialization=========" + bean.getClass());
//返回具體實例的代理對象
return bean;
}
/**
* 是在bean init方法執行之后觸發的
*/
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("=========postProcessAfterInitialization=========" + bean.getClass());
return bean;
}
}
測試：
public class Test {
public static void main(String[] args) {
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext("com.zhihao.miao.bean.demo9");
Car car = context.getBean(Car.class);
System.out.println(car);
context.close();
}
}
打印結果：
=========postProcessBeforeInitialization=========class org.springframework.context.event.EventListenerMethodProcessor
=========postProcessAfterInitialization=========class org.springframework.context.event.EventListenerMethodProcessor
=========postProcessBeforeInitialization=========class org.springframework.context.event.DefaultEventListenerFactory
=========postProcessAfterInitialization=========class org.springframework.context.event.DefaultEventListenerFactory
=========postProcessBeforeInitialization=========class com.zhihao.miao.bean.demo9.MyConfig$$EnhancerBySpringCGLIB$$dbdd1e75
=========postProcessAfterInitialization=========class com.zhihao.miao.bean.demo9.MyConfig$$EnhancerBySpringCGLIB$$dbdd1e75
=========set=========
=========postProcessBeforeInitialization=========class com.zhihao.miao.bean.demo9.Car
===== Car init ==========
=========postProcessAfterInitialization=========class com.zhihao.miao.bean.demo9.Car
com.zhihao.miao.bean.demo9.Car@2d127a61
Apply this BeanPostProcessor to the given new bean instance before any bean initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
or a custom init-method). The bean will already be populated with property values.
The returned bean instance may be a wrapper around the original.
在任何bean初始化回調之前將此BeanPostProcessor應用于給定的新bean實例（如InitializingBean的afterPropertiesSet（也相當于初始化方法）或自定義init方法）。 該bean將已經使用屬性值進行填充。返回的bean實例可能是原始實例的封裝。
Apply this BeanPostProcessor to the given new bean instance after any bean
initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
or a custom init-method). The bean will already be populated with property values.
The returned bean instance may be a wrapper around the original.
在任何bean之后，將此BeanPostProcessor應用于給定的新Bean實例初始化回調（如InitializingBean的 afterPropertiesSet或自定義init方法）。 該bean將已經使用屬性值進行填充。返回的bean實例可能是原始實例的封裝。
In case of a FactoryBean, this callback will be invoked for both the FactoryBean
instance and the objects created by the FactoryBean (as of Spring 2.0). The
post-processor can decide whether to apply to either the FactoryBean or created
objects or both through corresponding {@code bean instanceof FactoryBean} checks.
在FactoryBean的情況下，被回調指定在FactoryBean實例或者FactoryBean創建的實例（從Spring 2.0開始）。該后處理器可以決定是應用于FactoryBean還是創建對象或兩者通過相應的{@code bean instanceof FactoryBean}檢查。
This callback will also be invoked after a short-circuiting triggered by a
{@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,in contrast to all other BeanPostProcessor callbacks.
回調函數將被執行在InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation的短路觸發，與所有的BeanPostProcessor回調函數相反。
自己寫一個demo
定義一個接口SpringContextAware，只要類實現這個接口SpringContextAware，就會自動得把ApplicationContext對象注入到當前對象的屬性中。是不是很類似ApplicationContextAware的實現原理
定義接口：
@Component
public interface SpringContextAware {
void setApplicationContext(ApplicationContext applicationContext);
}
自己定義實例類繼承SpringContextAware接口：
@Component
public class Dog implements SpringContextAware {
private ApplicationContext applicationContext;
public void setApplicationContext(ApplicationContext applicationContext) {
this.applicationContext = applicationContext;
}
public void show(){
System.out.println("dog:"+applicationContext.getClass());
}
}
定義一個類實現BeanPostProcessor，然后在postProcessBeforeInitialization中判斷是否是實現SpringContextAware接口的實例
@Component
public class ContextBeanPostProcessor implements BeanPostProcessor {
@Autowired
private ApplicationContext applicationContext;
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if(bean instanceof SpringContextAware){
SpringContextAware sca = (SpringContextAware)bean;
sca.setApplicationContext(applicationContext);
}
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
// TODO Auto-generated method stub
return bean;
}
}
打印結果：
dog:class org.springframework.context.annotation.AnnotationConfigApplicationContext
