- Spring IOC 容器可以管理 Bean 的生命周期, Spring 允许在 Bean 生命周期的特定点执行定制的任务.
- 通过构造器或工厂方法创建 Bean 实例
- 为 Bean 的属性设置值和对其他 Bean 的引用
- 调用 Bean 的初始化方法
- Bean 可以使用了
- 当容器关闭时, 调用 Bean 的销毁方法
- 在 Bean 的声明里设置 init-method 和 destroy-method 属性, 为 Bean 指定初始化和销毁方法.
- 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.
- Bean 后置处理器对 IOC 容器里的所有 Bean 实例逐一处理, 而非单一实例. 其典型应用是: 检查 Bean 属性的正确性或根据特定的标准更改 Bean 的属性.
- 对Bean 后置处理器而言, 需要实现BeanPostProcessor接口. 在初始化方法被调用前后, Spring 将把每个 Bean 实例分别传递给上述接口的以下两个方法:
public class Car { public Car() { System.out.println("Car的无参构造器"); } public void setBrand(String brand) { System.out.println("setBrand......"); this.brand = brand; } private String brand; public void init() { System.out.println("init......"); } public void destroy() { System.out.println("destroy......"); } @Override public String toString() { return "Car [brand=" + brand + "]"; } }
package com.atguigu.spring.beans.cycle; import org.springframework.beans.BeansException; import org.springframework.beans.factory.config.BeanPostProcessor; public class MyBeanPostProcessor implements BeanPostProcessor { @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println("postProcessAfterInitialization:" + bean + "," + beanName); Car car = new Car(); car.setBrand("吉利"); return car; } @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { System.out.println("postProcessBeforeInitialization:" + bean + "," + beanName); if("car".equals(beanName)){ //... } return bean; } }
<?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.atguigu.spring.beans.cycle.Car" init-method="init" destroy-method="destroy"> <property name="brand" value="aodi"></property> </bean> <!-- 实现BeanPostProcessor这个接口,并具体提供两个方法的实现 postProcessBeforeInitialization(Object bean, String beanName)方法:init-method之前被调用 postProcessAfterInitialization(Object bean, String beanName)方法:init-method之后被调用 bean:bean实例本身 beanName:IOC容器配置的bean 的名字. 还回值:是实际上还回给用户的那个bean,注意:可以在以上两个方法中修改还回的bean,甚至还回一个新的bean --> <!-- 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.atguigu.spring.beans.cycle.MyBeanPostProcessor"></bean> </beans>
package com.atguigu.spring.beans.cycle; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Main { public static void main(String[] args) { ClassPathXmlApplicationContext apc = new ClassPathXmlApplicationContext("beans-cycle.xml"); Car car = (Car) apc.getBean("car"); System.out.println(car); //关闭IOC apc.close(); } }
结果:
六月 10, 2018 5:35:01 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh 信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@6193b845: startup date [Sun Jun 10 17:35:01 CST 2018]; root of context hierarchy 六月 10, 2018 5:35:01 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions 信息: Loading XML bean definitions from class path resource [beans-cycle.xml] Car的无参构造器 setBrand...... postProcessBeforeInitialization:Car [brand=aodi],car init...... postProcessAfterInitialization:Car [brand=aodi],car Car的无参构造器 setBrand...... Car [brand=吉利] 六月 10, 2018 5:35:02 下午 org.springframework.context.support.AbstractApplicationContext doClose 信息: Closing org.springframework.context.support.ClassPathXmlApplicationContext@6193b845: startup date [Sun Jun 10 17:35:01 CST 2018]; root of context hierarchy destroy......