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Spring中bean的生命周期(通俗易懂)

news 2025/9/9 15:36:36

具体流程

bean的生命周期分4个阶段：
1.实例化
2.属性赋值
3.初始化
4.销毁

实例化就是在内存中new()出一个对象，属性赋值就是给那些被@Autowired修饰的属性注入对象，销毁是在Spring容器关闭时触发，初始化的步骤比较多：

1.是否实现Aware的相关接口，调用重载方法
(BeanNameAware#setBeanName，
BeanClassLoaderAware#setBeanClassLoader，
BeanFactoryAware#setBeanFactory，
ApplicationContextAware#setApplicationContext)

2.是否有bean实现BeanPostProcessor接口，调用实现的postProcessBeforeInitialization方法(实现类加载时不调用自身实现的方法，调用其他实现类的)

3.是否实现InitializingBean接口，调用重载方法afterPropertiesSet方法

4.是否指定@Bean的initMethod属性，调用指定的方法(定义在bean对应的类里，不是配置类里)

5.是否有bean实现BeanPostProcessor接口，调用实现的postProcessAfterInitialization方法(和第2点同理)

话不多说，下面用代码来给出示例。

代码示例

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;public class A implements BeanNameAware, BeanFactoryAware, ApplicationContextAware, InitializingBean {public A() {System.out.println("a的构造函数");}@Overridepublic void setBeanName(String s) {System.out.println("初始化-setBeanName");}@Overridepublic void setBeanFactory(BeanFactory beanFactory) throws BeansException {System.out.println("初始化-setBeanFactory");}@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {System.out.println("初始化-setApplicationContext");}@Overridepublic void afterPropertiesSet() throws Exception {System.out.println("初始化-afterPropertiesSet");}public void init() {System.out.println("初始化-init");}}

import org.springframework.context.annotation.Bean;public class MyConfiguration  {@Bean(initMethod = "init")public A a() {return new A();}}

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Import;@Import(MyConfiguration.class)
public class BootStrap {public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(BootStrap.class);A bean = context.getBean(A.class);}}

运行启动类后，控制台打印：

在这里插入图片描述

这里单独再说下BeanPostProcessor，A类去实现它：

public class A implements BeanNameAware, BeanFactoryAware, ApplicationContextAware, InitializingBean, BeanPostProcessor{//...//其余的方法不动，就添加下面2个方法public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.println(beanName + "：初始化-beforeInitialization");return bean;}public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.println(beanName + "：初始化-afterInitialization");return bean;}}

再次运行启动类，控制台和之前的一样(A这个bean的初始化，没有调用实现的那2个方法)：

在这里插入图片描述

A类还原，不实现BeanPostProcessor；MyConfiguration类实现该接口：

import org.springframework.context.annotation.Bean;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;public class MyConfiguration implements BeanPostProcessor {@Bean(initMethod = "init")public A a() {return new A();}public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.println(beanName + "：初始化-beforeInitialization");return bean;}public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.println(beanName + "：初始化-afterInitialization");return bean;}}