Spring 容器中的 Bean 是有生命周期的，Bean 的生命周期是指 Bean 创建----> 初始化----> 销毁的过程，并且 Spring 允许 Bean 在初始化完成后以及销毁前执行特定的操作。下面是常用的三种指定特定操作的方法：

通过元素的init-method/destroy-method属性指定初始化之后 /销毁之前调用的操作方法；
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；
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，它是使用了InitDestroyAnnotationBeanPostProcessor后置处理器来实现的。
使用BeanPostProcessor后置处理器。

这几种配置方式，执行顺序是怎样的呢？我们通过例子来研究下：

Bean的列子类：InitBeanAndDestroyBean.java

package com.chenfeng.xiaolyuh.entity;
 
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
 
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
 
public class InitBeanAndDestroyBean implements InitializingBean, DisposableBean {
	public String say() {
		return "Hello!" + this.getClass().getName();
	}
 
	public InitBeanAndDestroyBean() {
		System.out.println("执行InitBeanAndDestroyBean构造方法");
	}
 
	@Override
	public void destroy() throws Exception {
		System.out.println("接口-执行InitBeanAndDestroyBeanTest：destroy方法");
	}
 
	@Override
	public void afterPropertiesSet() throws Exception {
		System.out.println("接口-执行InitBeanAndDestroyBeanTest：afterPropertiesSet方法");
	}
 
	@PostConstruct
	public void postConstructstroy() {
		System.out.println("注解-执行InitBeanAndDestroyBeanTest：preDestroy方法");
	}
 
	@PreDestroy
	public void preDestroy() {
		System.out.println("注解--执行InitBeanAndDestroyBeanTest：preDestroy方法");
	}
 
	public void initMethod() {
		System.out.println("XML配置-执行InitBeanAndDestroyBeanTest：init-method方法");
	}
 
	public void destroyMethod() {
		System.out.println("XML配置-执行InitBeanAndDestroyBeanTest：destroy-method方法");
	}
}

Spring配置类MyConfig.java

@Configuration // 声明成配置文件
@ComponentScan("com.chenfeng.xiaolyuh") // 扫描包
public class MyConfig {
	
	// 测试Bean的几种初始化和销毁方式，和执行顺序
	@Bean(initMethod="initMethod", destroyMethod="destroyMethod")
	public InitBeanAndDestroyBean initBeanAndDestroyBean() {
		return new InitBeanAndDestroyBean();
	}
}

测试类SpringIocTest.java

public class SpringIocTest {
    // 使用容器
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class, CatEntity.class);
 
    @Test
    public void contextTest() {
    	// 测试Bean的三种初始化、销毁方式和执行顺序
    	System.out.println(context.getBean(InitBeanAndDestroyBean.class));
    }
    
    @After
    public void closeContext() {
    	context.close();
    }
 
}

打印结果：

执行InitBeanAndDestroyBean构造方法
20:46:58.845 [main] DEBUG org.springframework.context.annotation.CommonAnnotationBeanPostProcessor - Found init method on class [com.xiaolyuh.init.destory.InitBeanAndDestroyBean]: public void com.xiaolyuh.init.destory.InitBeanAndDestroyBean.postConstructstroy()
20:46:58.846 [main] DEBUG org.springframework.context.annotation.CommonAnnotationBeanPostProcessor - Found destroy method on class [com.xiaolyuh.init.destory.InitBeanAndDestroyBean]: public void com.xiaolyuh.init.destory.InitBeanAndDestroyBean.preDestroy()
20:46:58.846 [main] DEBUG org.springframework.context.annotation.CommonAnnotationBeanPostProcessor - Registered init method on class [com.xiaolyuh.init.destory.InitBeanAndDestroyBean]: org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleElement@318a3b24
20:46:58.846 [main] DEBUG org.springframework.context.annotation.CommonAnnotationBeanPostProcessor - Registered destroy method on class [com.xiaolyuh.init.destory.InitBeanAndDestroyBean]: org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor$LifecycleElement@a27dd7d7
20:46:58.847 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Eagerly caching bean 'initBeanAndDestroyBean' to allow for resolving potential circular references
后置处理器-执行：postProcessBeforeInitialization 方法 处理：initBeanAndDestroyBean
20:46:58.850 [main] DEBUG org.springframework.context.annotation.CommonAnnotationBeanPostProcessor - Invoking init method on bean 'initBeanAndDestroyBean': public void com.xiaolyuh.init.destory.InitBeanAndDestroyBean.postConstructstroy()
注解-执行InitBeanAndDestroyBeanTest：preDestroy方法
20:46:58.850 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Invoking afterPropertiesSet() on bean with name 'initBeanAndDestroyBean'
接口-执行InitBeanAndDestroyBeanTest：afterPropertiesSet方法
20:46:58.851 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Invoking init method  'initMethod' on bean with name 'initBeanAndDestroyBean'
XML配置-执行InitBeanAndDestroyBeanTest：init-method方法
后置处理器-执行 执行：postProcessAfterInitialization 方法 处理：initBeanAndDestroyBean
20:46:58.851 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Finished creating instance of bean 'initBeanAndDestroyBean'
20:46:58.851 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
20:46:58.883 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Unable to locate LifecycleProcessor with name 'lifecycleProcessor': using default [org.springframework.context.support.DefaultLifecycleProcessor@1838ccb8]
20:46:58.883 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor'
20:46:58.885 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Could not find key 'spring.liveBeansView.mbeanDomain' in any property source


IOC容器完成初始化---->




打印 Spring 容器中的Bean  开始
org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalRequiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.event.internalEventListenerProcessor
org.springframework.context.event.internalEventListenerFactory
myConfig
initBeanBeanPostProcessor
initBeanAndDestroyBean
打印 Spring 容器中的Bean  结束


20:46:58.990 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'initBeanAndDestroyBean'
com.xiaolyuh.init.destory.InitBeanAndDestroyBean@5ba88be8
20:46:58.991 [main] INFO org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@5af97850: startup date [Mon Aug 26 20:46:58 CST 2019]; root of context hierarchy
20:46:58.991 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean 'lifecycleProcessor'
20:46:58.992 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Destroying singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@78691363: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.event.internalEventListenerProcessor,org.springframework.context.event.internalEventListenerFactory,myConfig,initBeanBeanPostProcessor,initBeanAndDestroyBean]; root of factory hierarchy
20:46:58.992 [main] DEBUG org.springframework.context.annotation.CommonAnnotationBeanPostProcessor - Invoking destroy method on bean 'initBeanAndDestroyBean': public void com.xiaolyuh.init.destory.InitBeanAndDestroyBean.preDestroy()
注解--执行InitBeanAndDestroyBeanTest：preDestroy方法
20:46:58.992 [main] DEBUG org.springframework.beans.factory.support.DisposableBeanAdapter - Invoking destroy() on bean with name 'initBeanAndDestroyBean'
接口-执行InitBeanAndDestroyBeanTest：destroy方法
20:46:58.993 [main] DEBUG org.springframework.beans.factory.support.DisposableBeanAdapter - Invoking destroy method 'destroyMethod' on bean with name 'initBeanAndDestroyBean'
XML配置-执行InitBeanAndDestroyBeanTest：destroy-method方法


关闭IOC容器---->

从执行结果可以看出：

Bean在实例化的过程中：Constructor > BeanPostProcessor.postProcessBeforeInitialization() > @PostConstruct > InitializingBean > init-method > BeanPostProcessor.postProcessAfterInitialization() > 容器初始化完成
Bean在销毁的过程中：@PreDestroy > DisposableBean > destroy-method > 销毁容器

如果Bean不是单例的，那么Spring不会去管理Bean，Spring 容器中只会存一个Bean标示。Bean的创建和初始化是在获取Bean的时候发生，并且在再容器关闭时不会调用Bean的销毁方法。非单例情况下，Bean的销毁是依靠GC。

源码

https://github.com/wyh-spring-ecosystem-student/spring-boot-student/tree/releases

spring-boot-student-spring 工程

layering-cache

为监控而生的多级缓存框架 layering-cache这是我开源的一个多级缓存框架的实现，如果有兴趣可以看一下下

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Spring Bean 的初始化和销毁的三种方式(Spring Bean 的生命周期)

源码

layering-cache

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