Java scheduled task test inherits TimerTask

First, introduce Java timer (java.util.Timer) It has the function of regularly executing planned tasks. By setting the interval of the timer, it will automatically execute after this interval. Pre-scheduled tasks (java.util. TimerTask)

For example: execute the task timer.schedule(TimerTask, 0, 60 * 60 * 1000) every hour.

The first parameter of the schedule() method is the task that needs to be executed. The type of this class is java.util.TimerTask, and the second parameter is execution. The waiting time before the task, where 0 means no waiting, the third parameter is the interval time, in milliseconds.

 /**
  * 定时任务测试类
  * @author admin
  *
  */
public class TimerScheduleDemo extends TimerTask { 
	 
	public TimerScheduleDemo() { 
	} 
	 
	@Override 
	public void run() { 
		print();
	} 
	 
	public static void main(String[] args) { 
		Timer timer = new Timer(); 
		long delay1 = 1 * 1000; 
		long period1 = 1000; 
		// 从现在开始 1*1000 秒钟之后，每隔 1 秒钟执行一次 
		timer.schedule(new TimerScheduleDemo(), delay1, period1); 
		/*long delay2 = 2 * 1000; 
		long period2 = 2000; 
		// 从现在开始 2 秒钟之后，每隔 2 秒钟执行一次 
		timer.schedule(new TimerScheduleDemo(), delay2, period2); */
	} 
	
	public static void print(){
		System.out.println("method start");
	}
	
}

But:

Since we hope that when the Web project starts, the timer can automatically start timing, so that throughout the life cycle of the Web project, tasks will be executed regularly, so start The timer class cannot be a general class. Here, the Servlet listener class is used to start the timer. By configuring this listener in the configuration file, let it automatically load and run when the project starts, and its survival period is the entire Web project life. Expect.

Task class main business code

/**
 * 定时器任务类:即调度任务类
 * @author admin
 */
public class DelFileTask extends TimerTask{


    private static boolean isRunning = false;    
    
    private ServletContext context = null;    
    
    public DelFileTask() {  
        super();  
    }  
      
    public DelFileTask(ServletContext context) {    
        this.context = context;    
    }    
    @Override  
    public void run() {  
          
        if (!isRunning) {  
               
            context.log("开始执行指定任务");   
            /** 
             * 自己的业务代码 
             */  
              
            isRunning = false;    
            context.log("指定任务执行结束");  
        } else {    
            context.log("上一次任务执行还未结束");    
       }  
    }  
	 
}

This class mainly inherits TimerTask and implements its run method

The following is the listening class that listens to the startup of the server and adds the task Go to the task stack

/**
 * servlet监听器:监听服务启动时执行调度任务
 * @author admin
 *
 */
public class ContextListener implements ServletContextListener{

	public ContextListener() { 
		
    }  
      
     private java.util.Timer timer = null;    
       
    /** 
     * 初始化定时器 
     * web 程序运行时候自动加载   
     */  
    @Override  
    public void contextInitialized(ServletContextEvent arg0) {  
          
    	/**
    	 * 设置一个定时器  
    	 */
        timer = new java.util.Timer(true);    
            
        arg0.getServletContext().log("定时器已启动");   
    
        /**
         * 定时器到指定的时间时,执行某个操作(如某个类,或方法)  
         */
        //设置执行时间  
        Calendar calendar =Calendar.getInstance();  
        int year = calendar.get(Calendar.YEAR);  
        int month = calendar.get(Calendar.MONTH);  
        int day =calendar.get(Calendar.DAY_OF_MONTH);//每天  
        //定制每天的16:10:00执行，  
        calendar.set(year, month, day, 16, 10, 00);  
        Date date = calendar.getTime();  
        System.out.println(date);  
        
        int period = 1000;  
        //每天的date时刻执行task，每隔persion 时间重复执行  
        timer.schedule(new DelFileTask(arg0.getServletContext()), date, period);
        
        //在 指定的date时刻执行task, 仅执行一次  
        //timer.schedule(new DelFileTask(arg0.getServletContext()), date);  
          
        arg0.getServletContext().log("已经添加任务调度表");    
          
    }  
  
    /** 
     * 销毁 
     */  
    @Override  
    public void contextDestroyed(ServletContextEvent arg0){  
  
        timer.cancel();  
        arg0.getServletContext().log("定时器销毁");  
    }  


}

This class is mainly used to set up a scheduler and let it execute tasks according to certain requirements.

The task class listener class has been implemented. The next step is to configure the listener in web.xml

  <listener>
  	<listener-class>ContextListener</listener-class>
  </listener>

At this point, a simple timer has basically been implemented and can run smoothly

Related recommendations:

How to use Java timer Timer-java tutorial

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