Spring入门学习（Bean的生命周期） 第九节

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Bean的生命周期

1. 创建需要的类Car.java

   package com.fafa.spring.beans.cycle;
   
   public class Car {
   
   	public Car(){
   		System.out.println("Car's constructor...");
   	}
   	
   	private String brand;
   
   	public void setBrand(String brand) {
   		System.out.println("setBrand...");
   		this.brand = brand;
   	}
   	
   	public void init2(){
   		System.out.println("init...");
   	}
   	
   	public void destroy(){
   		System.out.println("destroy....");
   	}
   
   	@Override
   	public String toString() {
   		return "Car [brand=" + brand + "]";
   	}
   }
   

2. 创建配置文件beans-cycle.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="car" class="com.fafa.spring.beans.cycle.Car"
   		init-method="init2" destroy-method="destroy">
   		<property name="brand" value="Audi"></property>
   	</bean>
   	
   	<!-- 
   		实现 BeanPostProcessor 接口，并具体提供
   		Object postProcessBeforeInitialization(Object bean, String beanName)：init-method 之前被调用
   		Object postProcessAfterInitialization(Object bean, String beanName)：init-method 之后被调用
   		两个方法的实现 
   		bean：bean实例本身
   		beanName：IOC容器配置的bean名字
   		返回值：是实际上返回给用户的那个bean，注意：可以在以上两个方法中修改返回的bean，甚至返回一个新的bean
   	-->
   </beans>
   

3. 创建测试方法：

   @Test
   public void testCycle(){
   	ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("classpath*:beans-cycle.xml");
   	Car car = (Car) ctx.getBean("car");
   	System.out.println(car);
   	ctx.close();
   }
   

   测试结果：

   Car's constructor...
   setBrand...
   init...
   Car [brand=Audi]
   十二月 31, 2018 8:13:08 下午 org.springframework.context.support.ClassPathXmlApplicationContext doClose
   信息: Closing org.springframework.context.support.ClassPathXmlApplicationContext@25ed7c33: startup date [Mon Dec 31 20:13:08 CST 2018]; root of context hierarchy
   destroy....
   

4. 创建一个MyBeanPostProcessor类继承自BeanPostProcessor类，此时可以对特定的一些bean做处理：

   package com.fafa.spring.beans.cycle;
   import org.springframework.beans.BeansException;
   import org.springframework.beans.factory.config.BeanPostProcessor;
   
   public class MyBeanPostProcessor implements BeanPostProcessor {
   
   	public Object postProcessBeforeInitialization(Object bean, String beanName)
   			throws BeansException {
   		System.out.println("postProcessBeforeInitialization:" + bean + ", " + beanName);
   		if("car".equals(beanName)){
   			//...
   		}
   		return bean;
   	}
   
   	public Object postProcessAfterInitialization(Object bean, String beanName)
   			throws BeansException {
   		System.out.println("postProcessAfterInitialization:" + bean + ", " + beanName);
   		Car car = new Car();
   		car.setBrand("Ford");
   		return car;
   	}
   }
   

   在XML中加入：

   <!-- 配置bean的后置处理器，不需要配置id，IOC容器自动识别是一个BeanPostProcessor-->
   <bean class="com.fafa.spring.beans.cycle.MyBeanPostProcessor"></bean>
   

    测试结果：
   

   Car's constructor...
   setBrand...
   postProcessBeforeInitialization:Car [brand=Audi], car
   init...
   postProcessAfterInitialization:Car [brand=Audi], car
   Car's constructor...
   setBrand...
   Car [brand=Ford]
   destroy....