Bean的初始化流程

技术2024-01-25 94

通过main函数启动spring容器加载bean时，会有以下流程：

1、通过实现BeanFactoryPostProcessor并覆盖postProcessBeanFactory()可以在spring容器初始化时拿到ConfigurableListableBeanFactory的实例，ConfigurableListableBeanFactory是所有bean的容器，也是BeanFactory的基础实现。此处可以对ConfigurableListableBeanFactory做扩展。

2、执行当前bean的构造函数

3、实现了BeanNameAware的接口会执行setBeanName()可以拿到bean的id

4、实现了BeanFactoryAware的接口会执行setBeanFactory()可以拿到beanFactory实例

5、执行init-method即@PostConstruct

6、实现了InitializingBean的接口的会执行afterPropertiesSet()，该方法没有参数，仅仅是作为通知

7、继承了InstantiationAwareBeanPostProcessorAdapter并重写了其中的postProcessBeforeInstantiation方法则会拿到bean的Class类型实例和beanName

8、继承了InstantiationAwareBeanPostProcessorAdapter并重写了其中的postProcessAfterInstantiation方法则会拿到bean的实例和beanName

9、继承了InstantiationAwareBeanPostProcessorAdapter并重写了其中的postProcessPropertyValues方法则会拿到bean的实例、bean的名称、属性值、属性描述符

10、继承了InstantiationAwareBeanPostProcessorAdapter并重写了其中的postProcessAfterInitialization方法则会拿到bean的实例和beanName

11、执行destroy前的回调

12、destroy之后的回调

一个栗子：

github:https://github.com/a422478514/java-practice/tree/master/src/main/java/com/daquan/_202007/_01/spring/beanlifecycle

MyBean:

import org.springframework.beans.BeansException; import org.springframework.beans.PropertyValues; import org.springframework.beans.factory.*; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.config.BeanPostProcessor; import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor; import org.springframework.stereotype.Service; import javax.annotation.PostConstruct; import javax.annotation.PreDestroy; import java.beans.PropertyDescriptor; @Service public class MyBean implements BeanPostProcessor, InstantiationAwareBeanPostProcessor, BeanNameAware, BeanFactoryAware, InitializingBean, DisposableBean { @Autowired private MyBeanFactoryPostProcessor myBeanFactoryPostProcessor; public MyBean(){ System.out.println("MyBean"); } @PostConstruct public void init(){ System.out.println("init"); } @PreDestroy public void preDestroy(){ System.out.println("preDestroy"); } @Override public void setBeanFactory(BeanFactory beanFactory) throws BeansException { System.out.println("setBeanFactory"); } @Override public void setBeanName(String s) { System.out.println("setBeanName"); } @Override public void destroy() throws Exception { System.out.println("destroy"); } @Override public void afterPropertiesSet() throws Exception { System.out.println("afterPropertiesSet"); } }

MyBeanFactoryPostProcessor:

import org.springframework.beans.BeansException; import org.springframework.beans.factory.config.BeanFactoryPostProcessor; import org.springframework.beans.factory.config.ConfigurableListableBeanFactory; import org.springframework.stereotype.Service; @Service public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor { @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException { System.out.println("configurableListableBeanFactory"); } }

MyInstantiationAwareBeanPostProcessor

import org.springframework.beans.BeansException; import org.springframework.beans.PropertyValues; import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessorAdapter; import org.springframework.stereotype.Service; import java.beans.PropertyDescriptor; /** * 通过继承InstantiationAwareBeanPostProcessorAdapter并覆盖其中的方法来实现多个扩展 */ @Service public class MyInstantiationAwareBeanPostProcessor extends InstantiationAwareBeanPostProcessorAdapter { // 接口方法、实例化Bean之前调用 @Override public Object postProcessBeforeInstantiation(Class beanClass,String beanName) throws BeansException { System.out.println("postProcessBeforeInstantiation"); return null; } // 接口方法、实例化Bean之后调用 @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println("postProcessAfterInitialization"); return bean; } // 接口方法、设置某个属性时调用 @Override public PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException { System.out.println("postProcessPropertyValues"); return pvs; } @Override public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException { System.out.println("postProcessAfterInstantiation"); return true; } }

TestMyBeanLifecycle

import org.springframework.context.support.ClassPathXmlApplicationContext; public class TestMyBeanLifecycle { public static void main(String[] args) { System.out.println("加载spring容器"); ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext("application.xml"); MyBean myBean = (MyBean) classPathXmlApplicationContext.getBean("myBean"); //执行下优雅关机，否则bean的destroy方法不会被调用 classPathXmlApplicationContext.registerShutdownHook(); } }

application.xml

<?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 http://www.springframework.org/schema/beans/spring-beans-4.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.1.xsd"> <context:annotation-config />  <context:component-scan base-package="com.daquan._202007._01.spring.beanlifecycle" /> </beans>

运行结果：

configurableListableBeanFactory MyBean setBeanName setBeanFactory init afterPropertiesSet postProcessBeforeInstantiation postProcessAfterInstantiation postProcessPropertyValues postProcessAfterInitialization postProcessBeforeInstantiation postProcessAfterInstantiation postProcessPropertyValues postProcessAfterInitialization preDestroy destroy

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