Spring IoC 容器 - Bean 后置处理器 - 《编程知识库》

Bean 后置处理器允许在调用初始化方法前后对 Bean 进行额外的处理
在**Spring**容器通过插入一个或多个**BeanPostProcessor**的实现来完成实例化，配置和初始化一个bean之后实现一些自定义逻辑回调方法
配置多个**BeanPostProcessor**接口，通过设置**BeanPostProcessor**实现的Ordered接口提供的**Order**属性来控制这些**BeanPostProcessor**接口的执行顺序，实现**Ordered.getOrder()**方法，返回值越小，执行顺序越靠前
在自定义的的**BeanPostProcessor**接口实现类中，要实现以下的两个抽象方法**BeanPostProcessor.postProcessBeforeInitialization(Object, String)**和**BeanPostProcessor.postProcessAfterInitialization(Object, String)**，注意命名要准确，否则会出现：**“ The type InitHelloWorld must implement the inherited abstract method BeanPostProcessorpostProcessBeforeInitialization(Object, String) ”**之类的错误
案例代码：
Person.java

package com.baklib.custom;
public class Person {
    private String name;
    private String carType;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getCarType() {
        return carType;
    }
    public void setCarType(String carType) {
        this.carType = carType;
    }
    public void buyCar(){
        System.out.println(this.getName()+"购买了"+this.getCarType()+"!");
    }
    public void init(){
        System.out.println("进入4S店");
    }
    public void destroy(){
        System.out.println("离开4S店");
    }
}

InitPerson0.java

package com.baklib.custom;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.Ordered;
public class InitPerson0 implements BeanPostProcessor, Ordered {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(this.getClass()+" BeforeInitialization0: "+beanName+"\tOrder: "+this.getOrder());
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(this.getClass()+" AfterInitialization0: "+beanName+"\tOrder: "+this.getOrder());
        return bean;
    }
    @Override
    public int getOrder() {
        return 5;
    }
}

InitPerson1.java

package com.baklib.custom;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.Ordered;
public class InitPerson1 implements BeanPostProcessor, Ordered {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(this.getClass()+" BeforeInitialization1: "+beanName+"\tOrder: "+this.getOrder());
        return bean;
    }
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println(this.getClass()+" AfterInitialization1: "+beanName+"\tOrder: "+this.getOrder());
        return bean;
    }
    @Override
    public int getOrder() {
        return 3;
    }
}

MainApp.java

package com.baklib.custom;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class MainApp {
    public static void main(String[] args) {
        AbstractApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
        Person person = (Person) context.getBean("person");
        person.buyCar();
        context.registerShutdownHook();
    }
}

配置文件 Beans.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="person" class="com.baklib.custom.Person" init-method="init" destroy-method="destroy">
        <property name="name" value="张三" />
        <property name="carType" value="小轿车" />
    </bean>
    <bean class="com.baklib.custom.InitPerson0" />
    <bean class="com.baklib.custom.InitPerson1" />
</beans>

编写完以上代码，就可以运行这个程序，运行结束后，可以在控制台看到下面的信息

class com.baklib.custom.InitPerson1 BeforeInitialization1: person    Order: 3
class com.baklib.custom.InitPerson0 BeforeInitialization0: person    Order: 5
进入4S店
class com.baklib.custom.InitPerson1 AfterInitialization1: person    Order: 3
class com.baklib.custom.InitPerson0 AfterInitialization0: person    Order: 5
张三购买了小轿车!
离开4S店