做一个合格的程序猿之浅析Spring IoC源码（四）分析BeanPostProcessor(1)

BeanPostProcessor是什么呢，有什么作用呢，打开源代码先看看

这个接口的注释中原作者说明了该接口的作用：

“工厂钩子允许用户自定义修改创建的bean实例，应用上下文可以在ben的定义中自动检测beanPostProecessor，并且将其应用于随后创建的任意bean中，并且可以通过factory给其他的类进行注册然后使用”

说白了，就是我们可以自定义的去修改spring给我们创建的类，给了我们一个二次修改bean的机会，这种设计思路与spring的“开闭原则”相符合，没有过度分装，举例来说，我们根据beanDefinition去查找一个Teacher,找到之后spring给我们实例化这个Teacher，但是我们用这个teacher的时候，发现这个teacher会抽烟，我们可以修改这个老师会抽烟的属性，这样就得到了一个完美的老师，这个完美的老师授课结束后，我们再告诉他你可以接着抽烟了，所以spring给我们想的还是很周到的~

 

再看这个接口定义的2个方法

BeanPostProcessor这个接口就2个方法，根据这2个方法的名称，我们就大概知道这2个方法的做什么的了

postProcessBeforeInitialization在“初始化之前处理”

postProcessAfterInitialization在“初始化之后处理”

废话不多说，我们就实现一个上面讲述的例子，大家更加深入的理解一下BeanPostProcessor这个作用

Teacher.java

package org.study.spring.beanpostprocessor.demo;public class Teacher {/** * 老师的姓名 */private String name;/** * 年龄 */private int age;/** * 是否抽烟 */private boolean smoking;/** * 老师教授的课程 */private String language;/** * 临时变量，默认抽烟 */private boolean tempSmoking = true;    public Teacher() {} public boolean isTempSmoking() {return tempSmoking;}public void setTempSmoking(boolean tempSmoking) {this.tempSmoking = tempSmoking;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public boolean isSmoking() {return smoking;}public void setSmoking(boolean smoking) {this.smoking = smoking;}public String getLanguage() {return language;}public void setLanguage(String language) {this.language = language;}public void teach(){System.out.println("I am :"+name+" and I will teach you :"+language + " and I "+(tempSmoking?"will":"will not")+" smoking");}}

ChangeTeacherSmokingBeanPostProcessor.java

package org.study.spring.beanpostprocessor.demo;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;public class ChangeTeacherSmokingBeanPostProcessor implements BeanPostProcessor{/** * 初始化之前处理 */public Object postProcessBeforeInitialization(Object bean, String beanName)throws BeansException {/** * 只处理该bean的类型是Teacher的 */if(bean instanceof Teacher){Teacher teacher = (Teacher)bean;/** * 实例化之前，要吧所有抽烟的都改成不抽烟的 */if(teacher.isSmoking()){((Teacher)bean).setTempSmoking(false);}}return bean;}public Object postProcessAfterInitialization(Object bean, String beanName)throws BeansException {return bean;}}

bean-post-processor-teacher.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"xmlns:mybatis-spring="http://mybatis.org/schema/mybatis-spring"xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jee="http://www.springframework.org/schema/jee"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsdhttp://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.2.xsdhttp://mybatis.org/schema/mybatis-spring http://mybatis.org/schema/mybatis-spring-1.2.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd">         <bean id="teacher" class="org.study.spring.beanpostprocessor.demo.Teacher">          <property name="name" value="孔浩"/>          <property name="age" value="32"/>          <property name="smoking" value="true"/>          <property name="language" value="java"/>        </bean>                <bean id="changeTeacher" class="org.study.spring.beanpostprocessor.demo.ChangeTeacherSmokingBeanPostProcessor"/>          </beans>

ChangeTeacherSmokingBeanPostProcessorTest.java

package org.study.spring.beanpostprocessor.demo;import org.junit.Test;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class ChangeTeacherSmokingBeanPostProcessorTest{@Testpublic void test2() throws Exception{ ApplicationContext applicationContext = new ClassPathXmlApplicationContext("bean-post-processor-teacher.xml"); Teacher teacher = applicationContext.getBean("teacher",Teacher.class); teacher.teach(); }}

运行结果

上面的例子只是说明，spring在初始化之前，给了我们开发者二次修改的机会，beanPostProcessor这个类是“spring”开闭原则的典型实现，下一节详细讲述它在项目中的具体运用~