https://blog.csdn.net/u011734144/article/details/72600932
http://www.cnblogs.com/lucas2/p/9430169.html
BeanPostProcessor：bean的后置处理器。在bean初始化前后进行一些处理工作。
public interface BeanPostProcessor {
/**
* Apply this BeanPostProcessor to the given new bean instance <i>before</i> 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.
* @param bean the new bean instance
* @param beanName the name of the bean
* @return the bean instance to use, either the original or a wrapped one;
* if {@code null}, no subsequent BeanPostProcessors will be invoked
* @throws org.springframework.beans.BeansException in case of errors
* @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
* 初始化之前工作
*/
Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
/**
* Apply this BeanPostProcessor to the given new bean instance <i>after</i> 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.
* <p>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.
* <p>This callback will also be invoked after a short-circuiting triggered by a
* {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
* in contrast to all other BeanPostProcessor callbacks.
* @param bean the new bean instance
* @param beanName the name of the bean
* @return the bean instance to use, either the original or a wrapped one;
* if {@code null}, no subsequent BeanPostProcessors will be invoked
* @throws org.springframework.beans.BeansException in case of errors
* @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
* @see org.springframework.beans.factory.FactoryBean
* 初始化之后工作
*/
Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}例子
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;
/**
* 后置处理器：初始化前后进行处理工作
* 将后置处理器加入到容器中
* @author lfy
*/
@Component
public class MyBeanPostProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("postProcessBeforeInitialization..."+beanName+"=>"+bean);
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("postProcessAfterInitialization..."+beanName+"=>"+bean);
return bean;
}
}import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
//@Component
public class Car implements InitializingBean, DisposableBean {
private String name;
public Car(String name) {
this.name = name;
System.out.println("car constructor...");
}
public void initMethod() {
System.out.println("car name: " + name);
System.out.println("car ... initMethod...");
}
public void destoryMethod() {
System.out.println("car ... destoryMethod...");
}
@Override
public void destroy() throws Exception {
System.out.println("car ...DisposableBean... destory");
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("car...InitializingBean...afterPropertiesSet");
}
@PostConstruct
public void postConstruct() {
System.out.println("car...postConstruct");
}
@PreDestroy
public void preDestory() {
System.out.println("car...preDestory");
}
}import com.atguigu.bean.Car;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
/**
* bean的生命周期：
* bean创建---初始化----销毁的过程
* 容器管理bean的生命周期；
* 我们可以自定义初始化和销毁方法；容器在bean进行到当前生命周期的时候来调用我们自定义的初始化和销毁方法
*
* 构造（对象创建）
* 单实例：在容器启动的时候创建对象
* 多实例：在每次获取的时候创建对象\
*
* BeanPostProcessor.postProcessBeforeInitialization
* 初始化：
* 对象创建完成，并赋值好，调用初始化方法。。。
* BeanPostProcessor.postProcessAfterInitialization
* 销毁：
* 单实例：容器关闭的时候
* 多实例：容器不会管理这个bean；容器不会调用销毁方法；
*
*
* 遍历得到容器中所有的BeanPostProcessor；挨个执行beforeInitialization，
* 一但返回null，跳出for循环，不会执行后面的BeanPostProcessor.postProcessorsBeforeInitialization
*
* BeanPostProcessor原理
* populateBean(beanName, mbd, instanceWrapper);给bean进行属性赋值
* initializeBean
* {
* applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
* invokeInitMethods(beanName, wrappedBean, mbd);执行自定义初始化
* applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
*}
*
*
*
* 1）、指定初始化和销毁方法；
* 通过@Bean指定init-method和destroy-method；
* 2）、通过让Bean实现InitializingBean（定义初始化逻辑），
* DisposableBean（定义销毁逻辑）;
* 3）、可以使用JSR250；
* @PostConstruct：在bean创建完成并且属性赋值完成；来执行初始化方法
* @PreDestroy：在容器销毁bean之前通知我们进行清理工作
* 4）、BeanPostProcessor【interface】：bean的后置处理器；
* 在bean初始化前后进行一些处理工作；
* postProcessBeforeInitialization:在初始化之前工作
* postProcessAfterInitialization:在初始化之后工作
*
* Spring底层对 BeanPostProcessor 的使用；
* bean赋值，注入其他组件，@Autowired，生命周期注解功能，@Async,xxx BeanPostProcessor;
*
* @author lfy
*
*/
@ComponentScan("com.atguigu.bean")
@Configuration
public class MainConfigOfLifeCycle {
@Bean(initMethod="initMethod",destroyMethod="destoryMethod")
public Car car(){
return new Car("audi");
}
}import com.atguigu.config.MainConfigOfLifeCycle;
import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class IOCTest_LifeCycle {
@Test
public void test01(){
//1、创建ioc容器
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class);
System.out.println("容器创建完毕");
//关闭容器
applicationContext.close();
}
}运行结果
从结果可以看出，spring管理的bean，会先执行postProcessBeforeInitialization，然后再执行初始化方法，如：@PostConstruct > InitializingBean > init-method
初始化：对象创建完成，并赋值好，调用初始化方法（@PostConstruct > InitializingBean > init-method）
初始化之前，调用BeanPostProcessor.postProcessBeforeInitialization
初始化之后，调用BeanPostProcessor.postProcessAfterInitialization
跟踪源码：
AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigOfLifeCycle.class)=>
refresh();=>
finishBeanFactoryInitialization(beanFactory);=>
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));=>
doGetBean(name, requiredType, null, false);=>
sharedInstance = getSingleton=>
return createBean(beanName, mbd, args);=>
Object beanInstance = doCreateBean(beanName, mbdToUse, args);=>
populateBean先为属性赋值，然后initializeBean
applyBeanPostProcessorsBeforeInitialization方法，遍历得到容器中所有的BeanPostProcessor，挨个执行beforeInitialization。一旦返回null，跳出for循环，不会执行后面的beanProcessor.postProcessAfterInitialization。
小总结
* BeanPostProcessor原理
* populateBean(beanName, mbd, instanceWrapper);给bean进行属性赋值
* initializeBean
* {
* applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
* invokeInitMethods(beanName, wrappedBean, mbd);执行自定义初始化
* applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
*}