简介
Bean的初始化方法和销毁方法是Bean生命周期级别的；而Lifecycle是容器生命周期级别的。如果我们想在容器本身的生命周期（比如容器启动完成后、停止之前）事件上做一些工作，可以使用LifeCycle接口。
源码
public interface Lifecycle {
void start();
void stop();
boolean isRunning();
}
- start：如果类A没在运行（isRunning返回false），则走该方法；否则不走该方法
- stop：如果类A在运行（isRunning返回true），则走该方法；否则不走该方法
- isRunning：返回true表示类A已经运行，返回false表示类A没运行
简单示例
isRunning返回true
代码
package com.example.config;
import org.springframework.context.Lifecycle;
import org.springframework.stereotype.Component;
@Component
public class MyLifeCycle implements Lifecycle {
@Override
public void start() {
System.out.println("start");
}
@Override
public void stop() {
System.out.println("stop");
}
@Override
public boolean isRunning() {
System.out.println("isRunning");
return true;
}
}
结果
启动时无打印
关闭时：
isRunning stop
isRunning返回false
package com.example.config;
import org.springframework.context.Lifecycle;
import org.springframework.stereotype.Component;
@Component
public class MyLifeCycle implements Lifecycle {
@Override
public void start() {
System.out.println("start");
}
@Override
public void stop() {
System.out.println("stop");
}
@Override
public boolean isRunning() {
System.out.println("isRunning");
return false;
}
}
结果
启动时无打印
关闭时
isRunning
改动isRunning值
我本以为，手动改isRunning返回值即可让它既执行start()又执行stop()，但我错了，如下所示：
package com.example.config;
import org.springframework.context.Lifecycle;
import org.springframework.stereotype.Component;
@Component
public class MyLifeCycle implements Lifecycle {
private volatile boolean running = false;
@Override
public void start() {
System.out.println("start");
running = true;
}
@Override
public void stop() {
System.out.println("stop");
}
@Override
public boolean isRunning() {
System.out.println("isRunning");
return running;
}
}
结果
启动时无打印
关闭时：
isRunning
显式调用start()
在上边“简单示例” 可以发现，无论怎么搞，都调用不到start()方法！！。有人说必须显式去调用它，如下所示：
public static void main(String[] args) {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(
"com.example.config.MyLifecycle");
ctx.start();
ctx.close();
}
但是，我只看到如下输出：
19:20:23.914 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@3ab39c39 19:20:23.924 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor' 19:20:23.944 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor' 19:20:23.944 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory' 19:20:23.944 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor' 19:20:23.944 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalCommonAnnotationProcessor' 19:20:23.964 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Found key 'spring.liveBeansView.mbeanDomain' in PropertySource 'systemProperties' with value of type String 19:20:23.974 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@3ab39c39, started on Tue Mar 09 19:20:23 CST 2021 19:20:23.974 [main] DEBUG org.springframework.core.env.PropertySourcesPropertyResolver - Found key 'spring.liveBeansView.mbeanDomain' in PropertySource 'systemProperties' with value of type String
对此，该有一张黑人问号脸。。。留到以后再看为什么会这样吧
请先 ！