【Java】Spring Bean的一生

Spring Bean的一生

When you work directly in Java, you can do anything you like with your objects and do not always need to rely on the container lifecycle.

前言:

在Ioc容器启动后相应的Bean并没有立即实例化，此时Ioc容器仅仅拥有所有对象的BeanDefinition(Bean对象在Spring中的描述,包含该Bean在容器中实例化所需的信息，通过解析xml/javaconfig后所得)

Spring Bean生命周期的管理

Spring bean factory能管理Beans的生命周期，通过实现InitializingBean和DisposableBean

这两个接口都只声明一个方法让我们可以初始化/关闭bean中的资源

当然在整个生命周期中也提供了一些Call Back Methods,这些方法类似于Servlet中的监听器的实现

  • 当Bean处于post-initialization阶段时，我们可以通过实现InitializingBean接口来实现afterPropertiesSet()
  • 当Bean处于pre-destruction 阶段时，我们可以实现DisposableBean 接口来实现destroy()方法

Spring Bean的生命周期图

Code Time

以Rick类交给Spring容器管理，方法顺序为其在Spring容器中的执行顺序

Rick.java

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public class Rick implements InitializingBean, DisposableBean {
    public Rick(){
        System.out.println("Rick is in [Rick] - Rick()");
    }

    public void customInit(){
        System.out.println("Rick is in [Rick] - customInit()");
    }

    @PostConstruct
    public void postConstruct(){
        System.out.println("Rick is in [@PostConstruct] - postConstruct()");
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("Rick is in [InitializingBean] - afterPropertiesSet()");
    }

    @PreDestroy
    public void preDestroy(){
        System.out.println("Rick is in [@PreDestroy] - preDestroy()");
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("Rick is in [DisposableBean] - destroy()");
    }

    public void customDestroy(){
        System.out.println("Rick is in [Rick] - customDestroy()");
    }
}

加入BeanPostProcess

RickBeanPostProcess.java

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public class RickBeanPostProcess implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof Rick) {
            System.out.println("Rick is in [BeanPostProcessor] - postProcessBeforeInitialization()");
        }

        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean instanceof Rick) {
            System.out.println("Rick is in [BeanPostProcessor] - postProcessAfterInitialization()");
        }
        return bean;
    }
}

配置类

RickConfig.java

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@Configuration
public class RickConfig {

    /**
     * 指定自定义初始化方法和自定义销毁方法
     * @return Rick
     */
    @Bean(initMethod = "customInit",destroyMethod = "customDestroy")
    public Rick rick(){
        return new Rick();
    }

    @Bean
    public RickBeanPostProcess rickBeanPostProcess(){
        return new RickBeanPostProcess();
    }
}

测试类

Client.java

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public class Client {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(RickConfig.class);
        ((AnnotationConfigApplicationContext) applicationContext).close();
    }
}

最终结果如下

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Rick is in [Rick] - Rick()
Rick is in [BeanPostProcessor] - postProcessBeforeInitialization()
Rick is in [@PostConstruct] - postConstruct()
Rick is in [InitializingBean] - afterPropertiesSet()
Rick is in [Rick] - customInit()
Rick is in [BeanPostProcessor] - postProcessAfterInitializa
Rick is in [@PreDestroy] - preDestroy()
Rick is in [DisposableBean] - destroy()
Rick is in [Rick] - customDestroy()

参考

Spring Framework Documentation

Spring Bean Life Cycle Explained

Spring Bean Life Cycle

Spring Boot Bean生命周期

Spring的Bean生命周期理解