Spring之Bean的生命周期

简介

1.SpringIOC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
2.SpringIOC容器对Bean的生命周期进行管理的过程：
	-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它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
3.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

代码示例

car.java

package com.lanoug.Bean.Circle;
public class Car {
	
	public Car() {
		System.out.println("Car's constructor...");
	}
	
	private String brand;

	public void setBrand(String brand) {
		System.out.println("Car's setBrand...");
		this.brand = brand;
	}
	
	public void init() {
		System.out.println("Car's init...");
	}

	public void destroy() {
		System.out.println("Car's destroy...");
	}
	@Override
	public String toString() {
		return "Car [brand=" + brand + "]";
	}	
}

beans-circle.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.lanoug.Bean.Circle.Car" init-method="init" destroy-method="destroy">
		<property name="brand" value="Baoma"></property>
	</bean>
</beans>

Test.java

package com.lanoug.Bean.Circle;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
	public static void main(String[] args) {
		ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("beans-circle.xml");
		Car car = (Car)ctx.getBean("car");
		System.out.println(car);
		// 关闭IOC容器
		ctx.close();
	}
}

运行结果

Bean后置处理器

简介

1.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
2.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。
3.对Bean后置处理器而言，需要实现Interface 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种方法：
postProcessBeforeInitialization(Object bean,String beanName)
postProcessAfterInitialization(Object bean,String beanName)

添加后置处理器之后的Bean的生命周期

Spring IOC容器对Bean的生命周期进行管理的过程：
1.通过构造器或工厂方法创建Bean实例
2.为Bean的属性设置值和对其它Bean的引用
3.将Bean的实例传递给Bean的后置处理器的postProcessBeforeInitialization方法
4.调用Bean的初始化方法
5.将Bean的实例传递给Bean的后置处理器的postProcessAfterInitialization方法
6.Bean可以使用了
7.当容器关闭时，调用Bean的销毁方法

MyBeanPostProcessor.java

package com.lanoug.Bean.Circle;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class MyBeanPostProcessor implements BeanPostProcessor {
	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) 
			throws BeansException {
		System.out.println("postProcessBeforeInitialization:" + bean + "," + beanName);
		if("car".equals(beanName)) {
			//.....
		}
		return bean;
	}
	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) 
			throws BeansException {
		System.out.println("postProcessAfterInitialization:" + bean + "," + beanName);
		return bean;
	}
}

beans-circle.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.lanoug.Bean.Circle.Car" init-method="init" destroy-method="destroy">
		<property name="brand" value="Baoma"></property>
	</bean>
	<!-- 
		实现BeanPostProcessor接口,并具体提供
		postProcessBeforeInitialization(Object bean, String beanName):init-method 之前被调用
		postProcessAfterInitialization(Object bean, String beanName):init-method 之后被调用
		的实现
		bean:bean 实例本身
		beanName:IOC容器中配置的bean的名字
		返回值:是实际上返回给用户的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
	 -->
	 <!-- 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.lanoug.Bean.Circle.MyBeanPostProcessor">	
	</bean>
</beans>

Test.java

package com.lanoug.Bean.Circle;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
	public static void main(String[] args) {
		ClassPathXmlApplicationContext ctx = new ClassPathXmlApplicationContext("beans-circle.xml");
		Car car = (Car)ctx.getBean("car");
		System.out.println(car);
		// 关闭IOC容器
		ctx.close();
	}
}

运行结果

信息: Loading XML bean definitions from class path resource [beans-circle.xml]
Car's constructor...
Car's setBrand...
postProcessBeforeInitialization:Car [brand=Baoma],car
Car's init...
postProcessAfterInitialization:Car [brand=Baoma],car
Car [brand=Baoma]
一月 02, 2019 9:42:13 下午 org.springframework.context.support.ClassPathXmlApplicationContext doClose
信息: Closing org.springframework.context.support.ClassPathXmlApplicationContext@63c12fb0: startup date [Wed Jan 02 21:42:13 CST 2019]; root of context hierarchy
Car's destroy...