shiro：LifecycleBeanPostProcessor的作用

在springboot中整合shiro的时候，在配置项中往往需要配置LifecycleBeanPostProcessor，他是用来管理shiro一些bean的生命周期

    @Bean("lifecycleBeanPostProcessor")
    public LifecycleBeanPostProcessor lifecycleBeanPostProcessor() {
        return new LifecycleBeanPostProcessor();
    }
    
    @Bean
	@DependsOn({"lifecycleBeanPostProcessor"})
    public DefaultAdvisorAutoProxyCreator defaultAdvisorAutoProxyCreator() {
        DefaultAdvisorAutoProxyCreator proxyCreator = new DefaultAdvisorAutoProxyCreator();
        proxyCreator.setProxyTargetClass(true);
        return proxyCreator;
    }

• DefaultAdvisorAutoProxyCreator是用来扫描上下文，寻找所有的Advistor(通知器），将这些Advisor应用到所有符合切入点的Bean中。所以必须在lifecycleBeanPostProcessor创建之后创建
• @DependsOn({“lifecycleBeanPostProcessor”})：创建DefaultAdvisorAutoProxyCreator 之前先创建LifecycleBeanPostProcessor

LifecycleBeanPostProcessor.java

public class LifecycleBeanPostProcessor implements DestructionAwareBeanPostProcessor, PriorityOrdered {
 
         .........................
         //省略。。。
 
 
    public Object postProcessBeforeInitialization(Object object, String name) throws BeansException {
        if (object instanceof Initializable) {
                ((Initializable) object).init();
        }
        return object;
    }
 
 
    public Object postProcessAfterInitialization(Object object, String name) throws BeansException {
        // Does nothing after initialization
        return object;
    }
 
    public void postProcessBeforeDestruction(Object object, String name) throws BeansException {
      if (object instanceof Destroyable) {
             ((Destroyable) object).destroy();
        }
    }
}

这里可以发现LifecycleBeanPostProcessor这个类实现了DestructionAwareBeanPostProcessor，

DestructionAwareBeanPostProcessor.java

public interface DestructionAwareBeanPostProcessor extends BeanPostProcessor {
    void postProcessBeforeDestruction(Object var1, String var2) throws BeansException;

    default boolean requiresDestruction(Object bean) {
        return true;
    }
}

这里可以发现DestructionAwareBeanPostProcessor这个类实现了BeanPostProcessor

BeanPostProcessor.java

public interface BeanPostProcessor {
    @Nullable
    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    @Nullable
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

再看看spring在初始化bean的时候：

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        //省略。。。
 
        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }
 
        //省略。。。
 
            invokeInitMethods(beanName, wrappedBean, mbd);
 
       //省略。。。
 
        if (mbd == null || !mbd.isSynthetic()) {
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }

其中applyBeanPostProcessorsBeforeInitialization和applyBeanPostProcessorsAfterInitialization就对应执行的是LifecycleBeanPostProcessor的postProcessBeforeInitialization和postProcessAfterInitialization，这里只举初始化的例子，销毁bean同理可得。

所有，可以知道LifecycleBeanPostProcessor将Initializable和Destroyable的实现类统一在其内部自动分别调用了Initializable.init()和Destroyable.destroy()方法，从而达到管理shiro bean生命周期的目的。