疑问：Spring 中构造器、init-method、@PostConstruct、afterPropertiesSet 孰先孰后，自动注入发生时间

一、前言

spring的一大优点就是扩展性很强，比如，在spring bean 的生命周期中，给我们预留了很多参与bean 的生命周期的方法。
大致梳理一下，有以下几种：

• 通过实现 InitializingBean/DisposableBean 接口来定制初始化之后/销毁之前的操作方法；
• 通过 <bean> 元素的 init-method/destroy-method属性指定初始化之后 /销毁之前调用的操作方法；
• 在指定方法上加上@PostConstruct 或@PreDestroy注解来制定该方法是在初始化之后还是销毁之前调用；
• 自定义 org.springframework.beans.factory.config.BeanPostProcessor ，来让 spring 回调我们的方法来参与 bean的生命周期。

但有个问题是，如果同时使用上面四种方式，会是什么结果？ 谁先，谁后呢？

二、验证

1、新建工程

我这边建立了测试工程，源码在文末：

xml中定义如下：

<bean class="com.ckl.springbeanlifecycle.DemoController" init-method="init" destroy-method="cleanUp"></bean>

重点是我们的DemoController，该类作为一个 bean，在xml中已经定义了，我们为该类，实现了各种接口，以及各种生命周期的相关注解：

 package com.ckl.springbeanlifecycle;

 import com.ckl.springbeanlifecycle.service.IDemoService;
 import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.beans.factory.annotation.Autowired;

 import javax.annotation.PostConstruct;
 import javax.annotation.PreDestroy;

 /**
  * desc:
  *
  * @author : caokunliang
  * creat_date: 2019/7/20 0020
  * creat_time: 18:45
  **/
 public class DemoController implements InitializingBean,DisposableBean {

     @Autowired
     private IDemoService iDemoService;

     public DemoController() {
         System.out.println();
         System.out.println("constructor ");
         System.out.println( "属性：" + iDemoService);
         System.out.println();
     }

     @Override
     public void destroy() throws Exception {
         System.out.println();
         System.out.println("implements DisposableBean interface");
         System.out.println( "属性iDemoService已注入：" + (iDemoService != null));
         System.out.println( "属性iDemoService已注入：" + iDemoService);
         System.out.println();
     }

     @Override
     public void afterPropertiesSet() throws Exception {
         System.out.println();
         System.out.println("afterPropertiesSet interface");
         System.out.println( "属性iDemoService已注入：" + (iDemoService != null));
         System.out.println( "属性iDemoService已注入：" + iDemoService);
         System.out.println();
     }

     @PostConstruct
     public void  postConstruct(){
         System.out.println();
         System.out.println("@PostConstrut....");
         System.out.println( "属性iDemoService已注入：" + (iDemoService != null));
         System.out.println( "属性iDemoService已注入：" + iDemoService);
         System.out.println();
     }

     @PreDestroy
     public void  preDestroy(){
         System.out.println();
         System.out.println("@PreDestroy.....");
         System.out.println( "属性iDemoService已注入：" + iDemoService);
         System.out.println();
     }

     public void init(){
         System.out.println();
         System.out.println("init-method by xml 配置文件");
         System.out.println( "属性iDemoService已注入：" + (iDemoService != null));
         System.out.println();
     }
     public void  cleanUp(){
         System.out.println();
         System.out.println("destroy-method by xml 配置文件");
         System.out.println( "属性iDemoService已注入：" + iDemoService);
         System.out.println();
     }
 }

因为我们还需要验证 org.springframework.beans.factory.config.BeanPostProcessor，所以我们自定义了一个 org.springframework.beans.factory.config.BeanPostProcessor：

 package com.ckl.springbeanlifecycle;

 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.stereotype.Component;

 import java.lang.reflect.Field;

 /**
  * desc:
  *
  * @author : caokunliang
  * creat_date: 2019/7/20 0020
  * creat_time: 18:52
  **/
 @Component
 public class MyBeanPostProcessor implements BeanPostProcessor {
     @Override
     public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
         if (bean instanceof DemoController){
             System.out.println();
             System.out.println("BeanPostProcessor:" + "postProcessBeforeInitialization");
             Field field = null;
             try {
                 field = bean.getClass().getDeclaredField("iDemoService");
                 field.setAccessible(true);
             } catch (NoSuchFieldException e) {
                 e.printStackTrace();
             }
             try {
                 Object o = field.get(bean);
                 System.out.println( "属性iDemoService已注入：" + (o != null));
                 System.out.println( "属性iDemoService已注入：" + o);
                 System.out.println();
             } catch (IllegalAccessException e) {
                 e.printStackTrace();
             }
         }
         return bean;
     }

     @Override
     public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
         if (bean instanceof DemoController){
             System.out.println();
             System.out.println("BeanPostProcessor:" + "postProcessAfterInitialization");
             Field field = null;
             try {
                 field = bean.getClass().getDeclaredField("iDemoService");
                 field.setAccessible(true);
             } catch (NoSuchFieldException e) {
                 e.printStackTrace();
             }
             try {
                 Object o = field.get(bean);
                 System.out.println( "属性iDemoService已注入：" + (o != null));
                 System.out.println( "属性iDemoService已注入：" + o);
                 System.out.println();
             } catch (IllegalAccessException e) {
                 e.printStackTrace();
             }
         }
         return bean;
     }
 }

2、运行

初始化时的顺序如下：

关闭容器时，执行顺序为：

3、扩展

可能部分朋友，还有这样的需求，即，在程序启动完成后，做点事情，比如，预热缓存之类的，那么，你可以这样：

 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.event.ContextRefreshedEvent;
 import org.springframework.stereotype.Service;

 /**
  * desc:
  *
  * @author : caokunliang
  * creat_date: 2018/11/20 0020
  * creat_time: 14:50
  **/
 @Service
 public class InitRunner implements ApplicationListener<ContextRefreshedEvent> {

     @Override
     public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
         //root application context
         if (contextRefreshedEvent.getApplicationContext().getParent() == null) {
             /**
              * 这里既是 root 容器初始化完毕后，会进入该分支，
              */
              todo。。。

         }else {
             /**
              * 如果是spring mvc的话， dispatchServlet对应的 applicationContext 会进入这个分支
              */

             ApplicationContext applicationContext = contextRefreshedEvent.getApplicationContext();
             todo。。。
         }

     }
 }

上面是针对启动时做的事情，关闭时，如果想做点事情，可以这样：

 package com.ceiec.webservice.init;

 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.context.ApplicationListener;
 import org.springframework.context.event.ContextClosedEvent;
 import org.springframework.stereotype.Service;

 /**
  * desc:
  *
  * @author : caokunliang
  * creat_date: 2018/11/20 0020
  * creat_time: 14:50
  **/
 @Service
 public class CloseRunner implements ApplicationListener<ContextClosedEvent> {
     private static final Logger logger = LoggerFactory.getLogger(CloseRunner.class);

     @Override
     public void onApplicationEvent(ContextClosedEvent contextClosedEvent) {
         logger.info("clean resources when close applicationContext");
         if(contextClosedEvent.getApplicationContext().getParent() == null){

         }

     }
 }

4、spring boot 的扩展

针对spring boot，也可以注册我们的 listener来参与生命周期。

实现 org.springframework.boot.SpringApplicationRunListener 即可，并将自定义的 listener 配置到 meta-inf 下的 spring.factories 文件。

举例如下：

 package com.ceiec.router.config;

 import com.ceiec.router.config.servletconfig.MyServletContext;
 import lombok.Data;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.SpringApplicationRunListener;
 import org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.env.MapPropertySource;
 import org.springframework.core.env.MutablePropertySources;
 import org.springframework.core.env.PropertySource;

 import javax.servlet.ServletContext;
 import java.util.Map;

 /**
  * desc:
  *
  * @author : caokunliang
  * creat_date: 2019/5/24 0024
  * creat_time: 20:07
  **/
 @Data
 @Slf4j
 public class MyListener implements SpringApplicationRunListener {

     public MyListener(SpringApplication application, String[] args) {
         super();
     }

     @Override
     public void starting() {

     }

     @Override
     public void environmentPrepared(ConfigurableEnvironment environment) {
         MutablePropertySources propertySources = environment.getPropertySources();
         for (PropertySource<?> propertySource : propertySources) {
             Object value = propertySource.getProperty("spring.liveBeansView.mbeanDomain");

             if (value != null) {
                 MapPropertySource source = (MapPropertySource) propertySource;
                 Map<String, Object> map = source.getSource();
                 map.remove("spring.liveBeansView.mbeanDomain");

                 log.info("spring.liveBeansView.mbeanDomain: after: {}",propertySource.getProperty("spring.liveBeansView.mbeanDomain"));
             }
         }
     }

     @Override
     public void contextPrepared(ConfigurableApplicationContext context) {
         log.info("contextPrepared");
         ServletContext servletContext = new MyServletContext();
         ServletWebServerApplicationContext applicationContext = (ServletWebServerApplicationContext) context;
         applicationContext.setServletContext(servletContext);
     }

     @Override
     public void contextLoaded(ConfigurableApplicationContext context) {
         //Not used.
     }

     @Override
     public void started(ConfigurableApplicationContext context) {

     }

     @Override
     public void running(ConfigurableApplicationContext context) {

     }

     @Override
     public void failed(ConfigurableApplicationContext context, Throwable exception) {

     }

 }

源码在交友网站： https://github.com/cctvckl/spring-bean-lifecycle