SpringBoot：Bean生命周期自定义初始化和销毁

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文章目录

前言

上篇文章详细讲诉了Bean的生命周期和作用域，在生命周期中提到了如何自定义初始化Bean，可能很多人不知道如何自定义初始化，这里详细补充讲解一下：使用@Bean注解指定初始化和销毁方法、实现InitializingBean接口和DisposableBean接口自定义初始化和销毁、@PostConstruct(初始化逻辑)和@PreDestroy(销毁逻辑)注解、使用BeanPostProcessor接口。

一、@Bean注解指定初始化和销毁方法

• 创建BeanTest类，自定义初始化方法和销毁方法。
• 在@Bean注解的参数中指定BeanTest自定义的初始化和销毁方法：
• 销毁方法只有在IOC容器关闭的时候才调用。

代码如下：

/**
 * @Version: 1.0.0
 * @Author: Dragon_王
 * @ClassName: dog
 * @Description: TODO描述
 * @Date: 2024/1/21 22:55
 */publicclassBeanTest{publicBeanTest(){System.out.println("BeanTest被创建");}publicvoidinit(){System.out.println("BeanTest被初始化");}publicvoiddestory(){System.out.println("BeanTest被销毁");}}/**
 * @Version: 1.0.0
 * @Author: Dragon_王
 * @ClassName: MyConfig
 * @Description: TODO描述
 * @Date: 2024/1/21 22:59
 */@Configuration@ComponentScan(("com.dragon.restart1"))publicclassMyConfig{@Bean(initMethod ="init",destroyMethod ="destory")publicBeanTestbeanTest(){returnnewBeanTest();}}//测试代码AnnotationConfigApplicationContext ct =newAnnotationConfigApplicationContext(MyConfig.class);System.out.println("IoC容器创建完成");

• 可以看到调用的是自定义的方法，这里解释一下，测试时，运行完代码块程序就结束了，所哟IoC容器就被关闭，所以调用了IoC销毁方法。同时可以看到初始化方法在对象创建完成后调用。
• 当组件的作用域为单例时在容器启动时即创建对象，而当作用域为原型（PROTOTYPE）时在每次获取对象的时候才创建对象。并且当作用域为原型（PROTOTYPE）时，IOC容器只负责创建Bean但不会管理Bean，所以IOC容器不会调用销毁方法。

二、实现InitializingBean接口和DisposableBean接口

看一下两接口的方法：

publicinterfaceInitializingBean{/**
     * Invoked by the containing {@code BeanFactory} after it has set all bean properties
     * and satisfied {@link BeanFactoryAware}, {@code ApplicationContextAware} etc.
     * <p>This method allows the bean instance to perform validation of its overall
     * configuration and final initialization when all bean properties have been set.
     * @throws Exception in the event of misconfiguration (such as failure to set an
     * essential property) or if initialization fails for any other reason
     * Bean都装配完成后执行初始化
     */voidafterPropertiesSet()throwsException;}====================================================================publicinterfaceDisposableBean{/**
     * Invoked by the containing {@code BeanFactory} on destruction of a bean.
     * @throws Exception in case of shutdown errors. Exceptions will get logged
     * but not rethrown to allow other beans to release their resources as well.
     */voiddestroy()throwsException;}

代码如下：

/**
 * @Version: 1.0.0
 * @Author: Dragon_王
 * @ClassName: BeanTest1
 * @Description: TODO描述
 * @Date: 2024/1/21 23:25
 */publicclassBeanTest1implementsInitializingBean,DisposableBean{@Overridepublicvoiddestroy()throwsException{System.out.println("BeanTest1销毁");}@OverridepublicvoidafterPropertiesSet()throwsException{System.out.println("BeanTest1初始化");}publicBeanTest1(){System.out.println("BeanTest1被创建");}}=========================@Configuration@ComponentScan(("com.dragon.restart1"))publicclassMyConfig{@BeanpublicBeanTest1beanTest1(){returnnewBeanTest1();}}

三、@PostConstruct(初始化逻辑)和@PreDestroy(销毁逻辑)注解

• 被@PostConstruct修饰的方法会在服务器加载Servlet的时候运行，并且只会被服务器调用一次，类似于Serclet的inti()方法。
• 被@PostConstruct修饰的方法会在构造函数之后，init()方法之前运行。
• 被@PreDestroy修饰的方法会在服务器卸载Servlet的时候运行，并且只会被服务器调用一次，类似于Servlet的destroy()方法。被@PreDestroy修饰的方法会在destroy()方法之后运行，在Servlet被彻底卸载之前。

代码如下：

/**
 * @Version: 1.0.0
 * @Author: Dragon_王
 * @ClassName: BeanTest2
 * @Description: TODO描述
 * @Date: 2024/1/21 23:32
 */publicclassBeanTest2{publicBeanTest2(){System.out.println("BeanTest2被创建");}@PostConstructpublicvoidinit(){System.out.println("BeanTest2被初始化");}@PreDestroypublicvoiddestory(){System.out.println("BeanTest2被销毁");}}========================//@Configuration@ComponentScan(("com.dragon.restart1"))publicclassMyConfig{@BeanpublicBeanTest2beanTest2(){returnnewBeanTest2();}}

四、BeanPostProcessor接口

BeanPostProcessor又叫Bean的后置处理器，是Spring框架中IOC容器提供的一个扩展接口，在Bean初始化的前后进行一些处理工作。

BeanPostProcessor的源码如下：

publicinterfaceBeanPostProcessor{/**
     * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
     * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
     * or a custom init-method). The bean will already be populated with property values.
     * The returned bean instance may be a wrapper around the original.
     * <p>The default implementation returns the given {@code bean} as-is.
     * @param bean the new bean instance
     * @param beanName the name of the bean
     * @return the bean instance to use, either the original or a wrapped one;
     * if {@code null}, no subsequent BeanPostProcessors will be invoked
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     */@Nullable//bean初始化方法调用前被调用defaultObjectpostProcessBeforeInitialization(Object bean,String beanName)throwsBeansException{return bean;}/**
     * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
     * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
     * or a custom init-method). The bean will already be populated with property values.
     * The returned bean instance may be a wrapper around the original.
     * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
     * instance and the objects created by the FactoryBean (as of Spring 2.0). The
     * post-processor can decide whether to apply to either the FactoryBean or created
     * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
     * <p>This callback will also be invoked after a short-circuiting triggered by a
     * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
     * in contrast to all other BeanPostProcessor callbacks.
     * <p>The default implementation returns the given {@code bean} as-is.
     * @param bean the new bean instance
     * @param beanName the name of the bean
     * @return the bean instance to use, either the original or a wrapped one;
     * if {@code null}, no subsequent BeanPostProcessors will be invoked
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     * @see org.springframework.beans.factory.FactoryBean
     */@Nullable//bean初始化方法调用后被调用defaultObjectpostProcessAfterInitialization(Object bean,String beanName)throwsBeansException{return bean;}

代码如下：

/**
 * @Version: 1.0.0
 * @Author: Dragon_王
 * @ClassName: MyBeanPostProcess
 * @Description: TODO描述
 * @Date: 2024/1/21 23:40
 */@ComponentpublicclassMyBeanPostProcessimplementsBeanPostProcessor{@OverridepublicObjectpostProcessBeforeInitialization(Object bean,String beanName)throwsBeansException{System.out.println("postProcessBeforeInitialization..."+beanName+"=>"+bean);return bean;}@OverridepublicObjectpostProcessAfterInitialization(Object bean,String beanName)throwsBeansException{System.out.println("postProcessAfterInitialization..."+beanName+"=>"+bean);return bean;}}============================@Configuration@ComponentScan(("com.dragon.restart1"))publicclassMyConfig{@BeanpublicBeanTest1beanTest1(){returnnewBeanTest1();}@BeanpublicBeanTest2beanTest2(){returnnewBeanTest2();}}

运行结果如下：

BeanTest1被创建
postProcessBeforeInitialization...beanTest1=>com.dragon.restart1.BeanTest1@111d5c97BeanTest1初始化
postProcessAfterInitialization...beanTest1=>com.dragon.restart1.BeanTest1@111d5c97BeanTest2被创建
postProcessBeforeInitialization...beanTest2=>com.dragon.restart1.BeanTest2@29c17c3dBeanTest2被初始化
postProcessAfterInitialization...beanTest2=>com.dragon.restart1.BeanTest2@29c17c3dIoC容器创建完成
BeanTest2被销毁
BeanTest1销毁

通过上述运行结果可以发现使用BeanPostProcessor的运行顺序为：
IOC容器实例化Bean---->调用BeanPostProcessor的postProcessBeforeInitialization方法---->调用bean实例的初始化方法---->调用BeanPostProcessor的postProcessAfterInitialization方法。

总结

以上就是Bean生命周期自定义初始化和销毁的讲解。