## Spring Bean 生命周期


### 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：

![](https://i.loli.net/2018/09/20/5ba2e83a54fd9.jpeg)

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:

```java
@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：

```java
@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:

```java
@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:

```xml
<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。

```java
@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：

```java
@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。