一、Bean 生命周期
Spring bean的生命周期很容易理解。当bean被实例化时，可能需要执行一些初始化以使其进入可用状态。类似地，当不再需要bean并从容器中移除bean时，可能需要进行一些清理。
虽然，在bean实例化及其销毁之间存在幕后发生的活动列表，但本章仅讨论两个重要的bean生命周期回调方法，这些方法在bean初始化及其销毁时是必需的。
要定义bean的设置和拆卸，我们只需使用initmethod和/或destroy-method参数声明<bean> 。init-method属性指定在实例化时立即在bean上调用的方法。类似地，destroy-method指定在从容器中删除bean之前调用的方法。
示例如下:
(1)编写HelloWord.java
package com.tutorialspoint;
public class HelloWorld {
private String message;
public void setMessage(String message){
this.message = message;
}
public void getMessage(){
System.out.println("Your Message : " + message);
}
public void init(){
System.out.println("Bean is going through init.");
}
public void destroy() {
System.out.println("Bean will destroy now.");
}
}
(2)编写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-4.0.xsd">
<bean id = "helloWorld" class = "com.tutorialspoint.HelloWorld" init-method = "init"
destroy-method = "destroy">
<property name = "message" value = "Hello World!"/>
</bean>
</beans>
(3)编写MainApp.java
package com.tutorialspoint;
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");
HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
obj.getMessage();
context.registerShutdownHook();
}
}
二、Bean Post 处理器
该BeanPostProcessor接口定义，你可以实现提供自己的实例化逻辑，依赖解析逻辑等，您还可以实现一些自定义的逻辑Spring容器完成实例化，配置，并通过在一个或多个堵塞初始化Bean后回调方法BeanPostProcessor实现。
您可以配置多个BeanPostProcessor接口，并且您可以通过设置订单属性来控制这些BeanPostProcessor接口的执行顺序，前提是BeanPostProcessor实现了Ordered接口。
BeanPostProcessors在bean（或对象）实例上运行，这意味着Spring IoC容器实例化一个bean实例，然后BeanPostProcessor接口完成它们的工作。
一个ApplicationContext的自动检测与该执行中定义的任何Bean的BeanPostProcessor接口，并注册这些Bean类如后处理器，被通过在容器创建bean的适当调用。
示例如下:
(1)编写HelloWorld.java
package com.tutorialspoint;
public class HelloWorld {
private String message;
public void setMessage(String message){
this.message = message;
}
public void getMessage(){
System.out.println("Your Message : " + message);
}
public void init(){
System.out.println("Bean is going through init.");
}
public void destroy(){
System.out.println("Bean will destroy now.");
}
}
(2)编写InitHelloWorld.java
package com.tutorialspoint;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.BeansException;
public class InitHelloWorld implements BeanPostProcessor {
public Object postProcessBeforeInitialization(Object bean, String beanName)
throws BeansException {
System.out.println("BeforeInitialization : " + beanName);
return bean; // you can return any other object as well
}
public Object postProcessAfterInitialization(Object bean, String beanName)
throws BeansException {
System.out.println("AfterInitialization : " + beanName);
return bean; // you can return any other object as well
}
}
(3)编写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-4.0.xsd">
<bean id = "helloWorld" class = "com.tutorialspoint.HelloWorld"
init-method = "init" destroy-method = "destroy">
<property name = "message" value = "Hello World!"/>
</bean>
<bean class = "com.tutorialspoint.InitHelloWorld" />
</beans>
(4)编写MainApp.java
package com.tutorialspoint;
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");
HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
obj.getMessage();
context.registerShutdownHook();
}
}
(5)运行MainApp.java中的main方法测试
结果如图:
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