Spring源码阅读——BeanFactoryPostProcessor与BeanPostProcessor

摘要

Spring IoC容器允许BeanFactoryPostProcessor在容器实例化任何bean之前读取bean的定义(配置元数据)，并可以修改它。

BeanFactoryPostProcessor：

BeanFactory的后置处理器（处理的对象是BeanFactory），BeanFactoryPostProcessor是在spring容器加载了bean的定义文件之后，在bean实例化之前执行的

BeanPostProcessor：

Bean的后置处理器（处理的对象是Bean）；可以在spring容器实例化bean之后，在执行bean的初始化方法前后，添加一些自己的处理逻辑。

使用

定义一个bean

package top.yuyufeng.learn.spring.bean;

/**
 * @author yuyufeng
 * @date 2018/10/10.
 */
public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

   //getters and setters
}

定义 BeanFactoryPostProcessor

package top.yuyufeng.learn.spring.postprocessor;

import org.springframework.beans.BeansException;
import org.springframework.beans.MutablePropertyValues;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;
import top.yuyufeng.learn.spring.bean.Person;


/**
 * @author yuyufeng
 * @date 2018/10/10.
 */
@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        String[] beanNames = beanFactory.getBeanDefinitionNames();
        for (String beanName : beanNames) {
            BeanDefinition bd = beanFactory.getBeanDefinition(beanName);
            if (bd.getBeanClassName().equals(Person.class.getName())) {
                System.out.println("#ProcessBeanFactory " + beanName);
                MutablePropertyValues mp = bd.getPropertyValues();
                mp.add("age", 0);
            }
        }
    }
}

定义BeanPostProcessor

package top.yuyufeng.learn.spring.postprocessor;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;
import top.yuyufeng.learn.spring.bean.Person;

/**
 * @author yuyufeng
 * @date 2018/10/10.
 */
@Component
public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (bean.getClass().equals(Person.class)) {
            Person person = (Person) bean;
            person.setName(person.getName() + "bf");
            System.out.println("#MyBeanPostProcessor.Before " + beanName);
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (bean.getClass().equals(Person.class)) {
            Person person = (Person) bean;
            person.setName(person.getName() + "af");
            System.out.println("#MyBeanPostProcessor. After  " + beanName);
        }
        return bean;
    }
}

配置Spring启动xml : spring-process.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <bean id="propertyPlaceholderConfigurerDao"
          class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="order" value="1"/>
        <property name="ignoreUnresolvablePlaceholders" value="true"/>
        <property name="locations">
            <list>
                <value>classpath:config.properties</value>
            </list>
        </property>
    </bean>

    <context:component-scan base-package="top.yuyufeng.learn.spring.postprocessor"/>

    <bean id="person1" class="top.yuyufeng.learn.spring.bean.Person">
        <constructor-arg index="0" value="小鱼"/>
        <constructor-arg index="1" value="25"/>
    </bean>

    <bean id="person2" class="top.yuyufeng.learn.spring.bean.Person">
        <constructor-arg index="0" value="小小"/>
        <constructor-arg index="1" value="26"/>
    </bean>
</beans>

调试：

package top.yuyufeng.learn.spring.postprocessor;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import top.yuyufeng.learn.spring.bean.Person;

/**
 * @author yuyufeng
 * @date 2018/10/10.
 */
public class App {
    public static void main(String[] args) {
        ApplicationContext ac = new ClassPathXmlApplicationContext("spring/spring-process.xml");

        Person p1 = (Person) ac.getBean("person1");
        System.out.println(p1);

        Person p2 = (Person) ac.getBean("person2");
        System.out.println(p2);
    }
}

运行结果：
#ProcessBeanFactory person1
#ProcessBeanFactory person2
#MyBeanPostProcessor.Before person1
#MyBeanPostProcessor. After person1
#MyBeanPostProcessor.Before person2
#MyBeanPostProcessor. After person2
Person{name=‘小鱼bfaf’, age=0}
Person{name=‘小小bfaf’, age=0}

我们在BeanFactoryPostProcessor，隐藏了Person对象的年龄，再去初始化对象的。在初始化的前后也可以做一些操作。

Spring的生命周期

看我们调试的打印顺序，我们来看下Spring的生命周期（去配置 init-method和实现InitializingBean接口）
顺序为：

ProcessBeanFactory
BeanPostProcessor.Before
afterPropertiesSet
initMethod
BeanPostProcessor. After