Spring IoC之Bean的生命周期 | IT宅-帅旋的专业知识分享

如上图：

1. 启动容器后，会对scope为singleton并且非懒加载的bean进行实例化(getBean方法触发实例化)；
2. 按照BeanDefinition定义信息配置信息，注入所有属性；
3. 如果实现了BeanNameAware接口，会调用接口的setBeanName方法，传入该bean的唯一标识，以便获取该bean的唯一标识；
4. 如果实现了BeanFactoryAware接口，会调用该接口的setBeanFactory方法，传入该bean的BeanFactory，以便获取bean的BeanFactory；
5. 如果实现了ApplicationContextAware接口，会调用该接口的setApplicationContext方法，传入该bean的ApplicationContext，以便获取该Bean的ApplicationContext；
6. 如果实现了BeanPostProcessor接口，则会回调该接口的postProcessBeforeInitialization方法；
7. 如果实现了InitializingBean接口，会调用该接口的afterPropertiesSet方法；
8. 如果配置了init-method方法，则执行此方法；
9. 如果实现了BeanPostProcessor接口，则会回调该接口的postProcessAfterInitialization方法；
10. 这个时候，就可以正式使用该bean了，对于scope为singleton的bean，Spring的ioc容器中会缓存一份该bean的实例，而对于prototype的bean，每次调用都会new一个新的对象，该对象的生命周期交给调用方管理，不由Spring容器管理；
11. 容器关闭的时候，如果bean实现了DisposableBean接口，则会回调该接口的destroy方法；
12. 如果bean配置了destroy-method方法，会执行此方法。

Spring Bean的生命周期中，主要包含三个阶段：初始化阶段，使用阶段，销毁阶段。其中初始化阶段和销毁阶段主要通过以下回调方式进行介入调整：3个Aware接口，两类BeanPostProcessor(自定义BeanPostProcessor和基于注解的CommonAnnotationBeanPostProcessor)，InitializingBean，DisposableBean，以及两个基于xml配置的方法(init-method, destroy-method)。如下图：

注意：需要在xml文件中需要以下配置以便开启CommonAnnotationBeanPostProcessor支持：

context:annotation-config/

这个配置会自动注册以下的post-processor： AutowiredAnnotationBeanPostProcessor, CommonAnnotationBeanPostProcessor, PersistenceAnnotationBeanPostProcessor, 还有前面提到的 RequiredAnnotationBeanPostProcessor。

参考：2.9、基于注解的容器配置

@Autowired, @Inject, @Resource以及@Value注解是通过BeanPostProcessor实现的，所以你不可以在你自己的BeanPostProcessor或者BeanFactoryPostProcessor中使用这些注解，而应该通过XML或者@Bean注解来配置。

下面是一个bean生命周期的实例：

LifeCycleBean，使用以上生命周期中各个回调方法：

/**
 * Created by arthinking on 17/11/2019.
 */
public class LifeCycleBean implements BeanNameAware, BeanFactoryAware, ApplicationContextAware, InitializingBean, DisposableBean {

    @Override
    public void setBeanName(String name) {
        System.out.println("==== 1.BeanNameAware.setBeanName: " + name);
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("==== 2.BeanFactoryAware.setBeanFactory: " + beanFactory);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("==== 3.ApplicationContextAware.setApplicationContext: " + applicationContext);
    }

    // ==== 4.BeanPostProcessor.postProcessBeforeInitialization

    /**
     * 由CommonAnnotationBeanPostProcessor处理, 相当于xml中的init-method配置
     */
    @PostConstruct
    public void initBean() {
        System.out.println("==== 5.CommonAnnotationBeanPostProcessor.postConstruct");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("==== 6.InitializingBean.afterPropertiesSet");
    }

    public void initMethod() {
        System.out.println("==== 7.init-method");
    }

    // ==== 8.BeanPostProcessor.postProcessAfterInitialization

    /**
     * 由CommonAnnotationBeanPostProcessor处理, 相当于xml中的destroy-method配置
     */
    @PreDestroy
    public void destroyBean() {
        System.out.println("==== 9.CommonAnnotationBeanPostProcessor.preDestroy");
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("==== 10.DisposableBean.destroy");
    }

    public void destroyMethod() {
        System.out.println("==== 11.destroy-method");
    }

}

自定义BeanPostProcessor：

/**
 * Created by arthinking on 17/11/2019.
 */
@Service
public class BeanPostService implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof LifeCycleBean) {
            System.out.println("==== 4.BeanPostProcessor.postProcessBeforeInitialization: " + beanName);
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof LifeCycleBean) {
            System.out.println("==== 8.BeanPostProcessor.postProcessAfterInitialization: " + beanName);
        }
        return bean;
    }

}

xml配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean name="lifeCycleBean" class="com.itzhai.spring.demo.beans.LifeCycleBean" init-method="initMethod" destroy-method="destroyMethod"/>
</beans>

输出结果如下：

2019-11-17 17:06:44.658  INFO 59661 --- [           main] .w.s.a.s.AnnotationActionEndpointMapping : Supporting [WS-Addressing August 2004, WS-Addressing 1.0]
==== 1.BeanNameAware.setBeanName: lifeCycleBean
==== 2.BeanFactoryAware.setBeanFactory: org.springframework.beans.factory.support.DefaultListableBeanFactory@76f4b65: ...
==== 3.ApplicationContextAware.setApplicationContext: org.springframework.web.context.support.GenericWebApplicationContext@e25951c, started on Sun Nov 17 17:06:42 CST 2019
==== 4.BeanPostProcessor.postProcessBeforeInitialization: lifeCycleBean
==== 5.CommonAnnotationBeanPostProcessor.postConstruct
==== 6.InitializingBean.afterPropertiesSet
==== 7.init-method
==== 8.BeanPostProcessor.postProcessAfterInitialization: lifeCycleBean
...
2019-11-17 17:06:49.385  INFO 59661 --- [extShutdownHook] o.s.s.concurrent.ThreadPoolTaskExecutor  : Shutting down ExecutorService 'applicationTaskExecutor'
==== 9.CommonAnnotationBeanPostProcessor.preDestroy
==== 10.DisposableBean.destroy
==== 11.destroy-method

Process finished with exit code 0

References

Top 50 Spring Interview Questions You Must Prepare In 2019

Spring Context and Bean Lifecycle callbacks: practical examples of usage

[Spring 20面试题]([https://github.com/Homiss/Java-interview-questions/blob/master/框架/Spring 面试题.md](https://github.com/Homiss/Java-interview-questions/blob/master/框架/Spring 面试题.md))