前言
Spring Bean 的生命周期在整个 Spring 中占有很重要的位置，掌握这些可以加深对 Spring 的理解。
首先看下生命周期图：
再谈生命周期之前有一点需要先明确：
Spring 只帮我们管理单例模式 Bean 的完整生命周期，对于 prototype 的 bean ，Spring 在创建好交给使用者之后则不会再管理后续的生命周期。
注解方式
在 bean 初始化时会经历几个阶段，首先可以使用注解 @PostConstruct, @PreDestroy 来在 bean 的创建和销毁阶段进行调用:
@Component public class AnnotationBean { private final static Logger LOGGER = LoggerFactory.getLogger(AnnotationBean.class); @PostConstruct public void start(){ LOGGER.info("AnnotationBean start"); } @PreDestroy public void destroy(){ LOGGER.info("AnnotationBean destroy"); } }
InitializingBean, DisposableBean 接口
还可以实现 InitializingBean,DisposableBean 这两个接口，也是在初始化以及销毁阶段调用：
@Service public class SpringLifeCycleService implements InitializingBean,DisposableBean{ private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleService.class); @Override public void afterPropertiesSet() throws Exception { LOGGER.info("SpringLifeCycleService start"); } @Override public void destroy() throws Exception { LOGGER.info("SpringLifeCycleService destroy"); } }
自定义初始化和销毁方法
也可以自定义方法用于在初始化、销毁阶段调用:
@Configuration public class LifeCycleConfig { @Bean(initMethod = "start", destroyMethod = "destroy") public SpringLifeCycle create(){ SpringLifeCycle springLifeCycle = new SpringLifeCycle() ; return springLifeCycle ; } } public class SpringLifeCycle{ private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycle.class); public void start(){ LOGGER.info("SpringLifeCycle start"); } public void destroy(){ LOGGER.info("SpringLifeCycle destroy"); } }
以上是在 SpringBoot 中可以这样配置，如果是原始的基于 XML 也是可以使用:
<bean class="com.crossoverjie.spring.SpringLifeCycle" init-method="start" destroy-method="destroy"> </bean>
来达到同样的效果。
实现 *Aware 接口
*Aware 接口可以用于在初始化 bean 时获得 Spring 中的一些对象，如获取 Spring 上下文等。
@Component public class SpringLifeCycleAware implements ApplicationContextAware { private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleAware.class); private ApplicationContext applicationContext ; @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { this.applicationContext = applicationContext ; LOGGER.info("SpringLifeCycleAware start"); } }
这样在 springLifeCycleAware 这个 bean 初始化会就会调用 setApplicationContext 方法，并可以获得 applicationContext 对象。
BeanPostProcessor 增强处理器
实现 BeanPostProcessor 接口，Spring 中所有 bean 在做初始化时都会调用该接口中的两个方法，可以用于对一些特殊的 bean 进行处理：
@Component public class SpringLifeCycleProcessor implements BeanPostProcessor { private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleProcessor.class); /** * 预初始化 初始化之前调用 * @param bean * @param beanName * @return * @throws BeansException */ @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { if ("annotationBean".equals(beanName)){ LOGGER.info("SpringLifeCycleProcessor start beanName={}",beanName); } return bean; } /** * 后初始化 bean 初始化完成调用 * @param bean * @param beanName * @return * @throws BeansException */ @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { if ("annotationBean".equals(beanName)){ LOGGER.info("SpringLifeCycleProcessor end beanName={}",beanName); } return bean; } }
执行之后观察结果：
018-03-21 00:40:24.856 [restartedMain] INFO c.c.s.p.SpringLifeCycleProcessor - SpringLifeCycleProcessor start beanName=annotationBean 2018-03-21 00:40:24.860 [restartedMain] INFO c.c.spring.annotation.AnnotationBean - AnnotationBean start 2018-03-21 00:40:24.861 [restartedMain] INFO c.c.s.p.SpringLifeCycleProcessor - SpringLifeCycleProcessor end beanName=annotationBean 2018-03-21 00:40:24.864 [restartedMain] INFO c.c.s.aware.SpringLifeCycleAware - SpringLifeCycleAware start 2018-03-21 00:40:24.867 [restartedMain] INFO c.c.s.service.SpringLifeCycleService - SpringLifeCycleService start 2018-03-21 00:40:24.887 [restartedMain] INFO c.c.spring.SpringLifeCycle - SpringLifeCycle start 2018-03-21 00:40:25.062 [restartedMain] INFO o.s.b.d.a.OptionalLiveReloadServer - LiveReload server is running on port 35729 2018-03-21 00:40:25.122 [restartedMain] INFO o.s.j.e.a.AnnotationMBeanExporter - Registering beans for JMX exposure on startup 2018-03-21 00:40:25.140 [restartedMain] INFO com.crossoverjie.Application - Started Application in 2.309 seconds (JVM running for 3.681) 2018-03-21 00:40:25.143 [restartedMain] INFO com.crossoverjie.Application - start ok! 2018-03-21 00:40:25.153 [Thread-8] INFO o.s.c.a.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@3913adad: startup date [Wed Mar 21 00:40:23 CST 2018]; root of context hierarchy 2018-03-21 00:40:25.155 [Thread-8] INFO o.s.j.e.a.AnnotationMBeanExporter - Unregistering JMX-exposed beans on shutdown 2018-03-21 00:40:25.156 [Thread-8] INFO c.c.spring.SpringLifeCycle - SpringLifeCycle destroy 2018-03-21 00:40:25.156 [Thread-8] INFO c.c.s.service.SpringLifeCycleService - SpringLifeCycleService destroy 2018-03-21 00:40:25.156 [Thread-8] INFO c.c.spring.annotation.AnnotationBean - AnnotationBean destroy
直到 Spring 上下文销毁时则会调用自定义的销毁方法以及实现了 DisposableBean 的 destroy() 方法。
