概述
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 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:
2017-09-16 00:40:24.856 [restartedMain] INFO c.c.s.p.SpringLifeCycleProcessor - SpringLifeCycleProcessor start beanName=annotationBean
2017-09-16 00:40:24.860 [restartedMain] INFO c.c.spring.annotation.AnnotationBean - AnnotationBean start
2017-09-16 00:40:24.861 [restartedMain] INFO c.c.s.p.SpringLifeCycleProcessor - SpringLifeCycleProcessor end beanName=annotationBean
2017-09-16 00:40:24.864 [restartedMain] INFO c.c.s.aware.SpringLifeCycleAware - SpringLifeCycleAware start
2017-09-16 00:40:24.867 [restartedMain] INFO c.c.s.service.SpringLifeCycleService - SpringLifeCycleService start
2017-09-16 00:40:24.887 [restartedMain] INFO c.c.spring.SpringLifeCycle - SpringLifeCycle start
2017-09-16 00:40:25.062 [restartedMain] INFO o.s.b.d.a.OptionalLiveReloadServer - LiveReload server is running on port 35729
2017-09-16 00:40:25.122 [restartedMain] INFO o.s.j.e.a.AnnotationMBeanExporter - Registering beans for JMX exposure on startup
2017-09-16 00:40:25.140 [restartedMain] INFO com.crossoverjie.Application - Started Application in 2.309 seconds (JVM running for 3.681)
2017-09-16 00:40:25.143 [restartedMain] INFO com.crossoverjie.Application - start ok!
2017-09-16 00:40:25.153 [Thread-8] INFO o.s.c.a.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@3913adad: startup date [Fri Sep 16 00:40:23 CST 2017]; root of context hierarchy
2017-09-16 00:40:25.155 [Thread-8] INFO o.s.j.e.a.AnnotationMBeanExporter - Unregistering JMX-exposed beans on shutdown
2017-09-16 00:40:25.156 [Thread-8] INFO c.c.spring.SpringLifeCycle - SpringLifeCycle destroy
2017-09-16 00:40:25.156 [Thread-8] INFO c.c.s.service.SpringLifeCycleService - SpringLifeCycleService destroy
2017-09-16 00:40:25.156 [Thread-8] INFO c.c.spring.annotation.AnnotationBean - AnnotationBean destroy
作者: Zealon
崇尚简单,一切简单自然的事物都是美好的。