Spring Bean 的初始化和銷燬的三種方式

Spring 容器中的 Bean 是有生命週期的，Bean 的生命週期是指 Bean 建立----> 初始化----> 銷燬 的過程，而且 Spring 容許 Bean 在初始化完成後以及銷燬前執行特定的操做。 下面是經常使用的三種指定特定操做的方法：

1. 經過<bean> 元素的init-method/destroy-method屬性指定初始化以後 /銷燬以前調用的操做方法；
2. 經過實現InitializingBean/DisposableBean 接口來定製初始化以後/銷燬以前的操做方法； 
3. 在指定方法上加上@PostConstruct或@PreDestroy註解來制定該方法是在初始化以後仍是銷燬以前調用，它是使用了InitDestroyAnnotationBeanPostProcessor後置處理器來實現的。
4. 使用BeanPostProcessor後置處理器。

這幾種配置方式，執行順序是怎樣的呢？咱們經過例子來研究下：

Bean的列子類：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("執行InitBeanAndDestroyBean構造方法");
	}
 
	@Override
	public void destroy() throws Exception {
		System.out.println("接口-執行InitBeanAndDestroyBeanTest：destroy方法");
	}
 
	@Override
	public void afterPropertiesSet() throws Exception {
		System.out.println("接口-執行InitBeanAndDestroyBeanTest：afterPropertiesSet方法");
	}
 
	@PostConstruct
	public void postConstructstroy() {
		System.out.println("註解-執行InitBeanAndDestroyBeanTest：preDestroy方法");
	}
 
	@PreDestroy
	public void preDestroy() {
		System.out.println("註解--執行InitBeanAndDestroyBeanTest：preDestroy方法");
	}
 
	public void initMethod() {
		System.out.println("XML配置-執行InitBeanAndDestroyBeanTest：init-method方法");
	}
 
	public void destroyMethod() {
		System.out.println("XML配置-執行InitBeanAndDestroyBeanTest：destroy-method方法");
	}
}

Spring配置類MyConfig.java

@Configuration // 聲明成配置文件
@ComponentScan("com.chenfeng.xiaolyuh") // 掃描包
public class MyConfig {
	
	// 測試Bean的幾種初始化和銷燬方式，和執行順序
	@Bean(initMethod="initMethod", destroyMethod="destroyMethod")
	public InitBeanAndDestroyBean initBeanAndDestroyBean() {
		return new InitBeanAndDestroyBean();
	}
}

測試類SpringIocTest.java

public class SpringIocTest {
    // 使用容器
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(MyConfig.class, CatEntity.class);
 
    @Test
    public void contextTest() {
    	// 測試Bean的三種初始化、銷燬方式和執行順序
    	System.out.println(context.getBean(InitBeanAndDestroyBean.class));
    }
    
    @After
    public void closeContext() {
    	context.close();
    }
 
}

打印結果：

執行InitBeanAndDestroyBean構造方法
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
後置處理器-執行：postProcessBeforeInitialization 方法 處理：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()
註解-執行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-執行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-執行InitBeanAndDestroyBeanTest：init-method方法
後置處理器-執行 執行：postProcessAfterInitialization 方法 處理：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  開始
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  結束


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()
註解--執行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-執行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-執行InitBeanAndDestroyBeanTest：destroy-method方法


關閉IOC容器---->

從執行結果能夠看出： 

• Bean在實例化的過程當中：Constructor > BeanPostProcessor.postProcessBeforeInitialization() > @PostConstruct > InitializingBean > init-method > BeanPostProcessor.postProcessAfterInitialization() > 容器初始化完成
• Bean在銷燬的過程當中：@PreDestroy > DisposableBean > destroy-method > 銷燬容器

若是Bean不是單例的，那麼Spring不會去管理Bean，Spring 容器中只會存一個Bean標示。Bean的建立和初始化是在獲取Bean的時候發生，而且在再容器關閉時不會調用Bean的銷燬方法。非單例狀況下，Bean的銷燬是依靠GC。

源碼

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

spring-boot-student-spring 工程

layering-cache

爲監控而生的多級緩存框架 layering-cache這是我開源的一個多級緩存框架的實現，若是有興趣能夠看一下下