一、实现原理：向JVM注册ShutdownHook,ShutdownHook用法如下：

package cn.edu.tju;

public class ShutdownHookTest {
  public static void main(String[] args) {
    Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
      @Override
      public void run() {
        System.out.println("this is a shutdown hook to jvm");
      }
    }));
    System.out.println("Hello,this is my world!");
  }
}

二、实现
创建bean，实现ExitCodeGenerator

getExitCodeGenerator(){
        return () -> 888;

    }

程序退出时，返回的code就为888