一.多线程基本篇-1.11 钩子程序

小咪咪 2022-12-10 01:20 98阅读 0赞

## 1.使用场景 ##

*  当程序正常退出,系统调用 System.exit方法
 *  虚拟机被关闭时
 *  程序抛出异常时
 *  可通过这些钩子在jvm关闭的时候进行内存清理、资源回收等工作

通过我们的程序中运行完之后都会进行一些清理工作,比如关闭数据库资源,同步等操作。这时我们的钩子函数addShutdownHook有了用武之地。

## 2.用法 ##

Runtime.getRuntime().addShutdownHook(Thread thread)

## 3.实战 ##

public
     class CaptureException{
        public static void main(String[] args){
            Runtime.getRuntime().addShutdownHook(new Thread(()->{
                System.out.println("The application will exit");
                notifyAndRelease();
            } ));
            
            int i = 0;
            while (true){
                 try{
                     Thread.sleep(1_000L);
                 }catch(Throwable e){
                   //ignore
                 }
                 System.out.println("I am working...");             
                 i++;
                 if (i > 20) throw new RuntimeException("error");
            }
    
        }
       
        public static void notifyAndRelease(){
           System.out.println("notify to the admin");
           try{
                Thread.sleep(1_000L);
           }catch(Throwable e){
             //ignore
           }
           System.out.println("Will release resource(file,socket,connections)");
           try{
                Thread.sleep(1_000L);
           }catch(Throwable e){
             //ignore
           }
    
           System.out.println("Release done");
         
              
        }
    } 
    
    
    -------------------------------------------------------------------------------------------
    kill 128964
    [root@localhost java]# java -cp . CaptureException
    I am working...
    ...
    I am working...
    
    The application will exit
    notify to the admin
    I am working...
    Will release resource(file,socket,connections)
    I am working...
    Exception in thread "main" java.lang.RuntimeException: error
            at CaptureException.main(CaptureException.java:17)
    Release done
    -------------------------------------------------------------------------------------------