shiro学习之LifecycleBeanPostProcessor的作用

在使用spring整合shiro的系统中，配置bean的时候往往要配置LifecycleBeanPostProcessor，一直没有深究这个的具体作用，只大概知道是用来管理shiro一些bean的生命周期。今天查了一下源码，总算揭开它的神秘面纱。

先来看看日常的配置：

id="lifecycleBeanPostProcessor" class="org.apache.shiro.spring.LifecycleBeanPostProcessor" />

id="annotationProxy"
class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"
depends-on="lifecycleBeanPostProcessor">
<property name="proxyTargetClass" value="true" />

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，所以用了depends-on=”lifecycleBeanPostProcessor”>
。

再看看LifecycleBeanPostProce：

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();
        }
    }
}

DestructionAwareBeanPostProcessor是什么?再深究：

public interface DestructionAwareBeanPostProcessor extends BeanPostProcessor {

    void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException;
}

BeanPostProcessor:

public interface BeanPostProcessor {
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}

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。

从此，可知道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。