Spring之后置处理器

 
Spring的后置处理器是Spring对外开发的重要扩展点，允许我们接入Bean的实例化流程中，以达到动态注册BeanDefinition、动态修改BeanDefinition、动态修改Bean的作用。
 
BeanFactoryPostProcessor
 

BeanFactory的后置处理器，在BeandefinitionMap填充完毕之后，Bean实例化之前执行。
BeanFactoryPostProcessor是一个接口规范，用于对BeanDefinition进行操作（注册、修改、删除）。

package org.springframework.beans.factory.config;

import org.springframework.beans.BeansException;

public interface BeanFactoryPostProcessor {

    void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

BeanFactoryPostProcessor

应用

方式一：自定义BeanFactoryPostProcessor接口实现类：实现BeanFactoryPostProcessor接口，并将实现类注册到Spring中，Spring就可以自动调用postProcessBeanFactory方法.

package com.blueStarWei.processor;

import org.springframework.beans.BeansException;

import org.springframework.beans.factory.config.BeanDefinition;

import org.springframework.beans.factory.config.BeanFactoryPostProcessor;

import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;

import org.springframework.beans.factory.support.DefaultListableBeanFactory;

import org.springframework.beans.factory.support.RootBeanDefinition;

import org.springframework.stereotype.Component;

@Component

public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

        // 注册

        BeanDefinition definition = new RootBeanDefinition();

        definition.setBeanClassName("com.blueStarWei.ObjectBeanFactory");

        //必须强制转换为DefaultListableBeanFactory才能注册\删除

        DefaultListableBeanFactory defaultListableBeanFactory = (DefaultListableBeanFactory) beanFactory;

        defaultListableBeanFactory.registerBeanDefinition("myBeanFactory",definition);

        //删除

        defaultListableBeanFactory.removeBeanDefinition("user");

        //修改

        BeanDefinition person = beanFactory.getBeanDefinition("person");

        person.setScope(BeanDefinition.SCOPE_PROTOTYPE);

    }

}

方式二：自定义BeanDefinitionRegistryPostProcessor接口实现类：BeanDefinitionRegistryPostProcessor接口是BeanFactoryPostProcessor接口的子接口，主要用于注册BeanDefinition。【先调用postProcessBeanDefinitionRegistry(),再调用postProcessBeanFactory()】

package com.blueStarWei.processor;

import org.springframework.beans.BeansException;

import org.springframework.beans.factory.config.BeanDefinition;

import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;

import org.springframework.beans.factory.support.BeanDefinitionRegistry;

import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;

import org.springframework.beans.factory.support.RootBeanDefinition;

import org.springframework.stereotype.Component;

@Component

public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {

    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {

        System.out.println(">>>>>>>1. postProcessBeanDefinitionRegistry");

        BeanDefinition definition = new RootBeanDefinition();

        definition.setBeanClassName("com.blueStarWei.ObjectBeanFactory");

        registry.registerBeanDefinition("myBeanFactory",definition);

    }

    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

        System.out.println(">>>>>>>>>>2. postProcessBeanFactory");

    }

}

注意：当方式一与方式二同时使用时，调用顺序为：
BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry()
BeanDefinitionRegistryPostProcessor.postProcessBeanFactory()
BeanFactoryPostProcessor.postProcessBeanFactory()

BeanPostProcessor

Bean的后置处理器，一般在Bean的初始化前后执行。Bean实例化之后，填充到单例池singletonObjects之前执行，会进行Bean的初始化。

BeanPostProcessor是一个接口规范，用于对Bean进行修改。

package org.springframework.beans.factory.config;

import org.springframework.beans.BeansException;

public interface BeanPostProcessor {

   /**

    * 在Bean的初始化之前执行

    */

   Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

   /**

    * 在Bean的初始化之后执行

    */

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

}

BeanPostProcessor

应用

使用动态代理进行Bean的功能增强

package com.blueStarWei.processor;

import org.springframework.beans.BeansException;

import org.springframework.beans.factory.config.BeanPostProcessor;

import java.lang.reflect.Proxy;

public class MyBeanPostProcessor implements BeanPostProcessor {

    @Override

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

        return bean;

    }

    /**

     * 打印方法调用时间日志

     * 注意：使用jdk自带的Proxy只能对有接口的类进行动态代理,直接代理POJO会报类型ClassCastException

     *

     */

    @Override

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

        Object beanProxy = Proxy.newProxyInstance(

                bean.getClass().getClassLoader(),

                bean.getClass().getInterfaces(),

                (proxy, method, args) -> {

                    long startTime = System.currentTimeMillis();

                    Object result = method.invoke(bean, args);

                    long endTime = System.currentTimeMillis();

                    System.out.println(beanName + "." + method.getName() + "执行时间：" + (endTime - startTime) + "ms.");

                    return result;

                }

        );

        return beanProxy;

    }

}

Spring之后置处理器的相关教程结束。