Spring源码阅读——BeanFactoryPostProcessor与BeanPostProcessor

拼搏现实的明天。 2022-05-08 08:44 220阅读 0赞

## 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