Java监听器，定时器

1、什么是监听器？

所谓的监听器就好像JS中所学的事件，以及Java程序贪食蛇中根据获取的键盘上不同的键值，来点击的时候改变蛇运动的方向。

2、监听器是怎么实现的？

了解这个之前，首先要了解一个小知识就是，源：监听的是谁；动作：触发条件；响应：当这个条件满足的时候会执行的函数。

3、具体代码如下(只是实现了其中的某些接口)：

package listener;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

@WebListener()
public class MyListener implements ServletContextAttributeListener,HttpSessionAttributeListener {


    @Override
    public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {
        System.out.println("属性被添加了");
    }

    @Override
    public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {
        System.out.println("属性被移除了");
    }

    @Override
    public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {
        System.out.println("属性被替换了");
    }

    @Override
    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("属性被添加了");
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("属性被移除了");
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("属性被替换了");
    }
}

补充：ServletContext对象：生命周期随着项目的启动而创建，随着项目的关闭而销毁。

4、什么是定时器？

比如说，我们想要让我所写的一篇文章在在某个时刻向一些地方进行推送，那么这个时候，我就需要用定时器

设置一个时间，在经过一段时间后就进行推送。

5、具体代码实现：

1、Timer

package listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.util.Calendar;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

public class ListenerDemo implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.HOUR_OF_DAY,14);//控制时
        calendar.set(Calendar.MINUTE,48);//控制分
        calendar.set(Calendar.SECOND,14);//控制秒
        Date date = calendar.getTime();//得出执行任务的时间
                /*定时器*/
        Timer timer = new Timer();
        timer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                System.out.println("1+1=2");
            }
        },date,1000*10);
             System.out.println("ServletContext创建了");
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("ServletContext销毁了");
    }
}

2、quartz

package org.quartz.examples.example4;
import java.util.Date;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.quartz.JobDetail;
import org.quartz.Scheduler;
import org.quartz.SchedulerFactory;
import org.quartz.SchedulerMetaData;
import org.quartz.SimpleTrigger;
import org.quartz.TriggerUtils;
import org.quartz.impl.StdSchedulerFactory;
/**
* This Example will demonstrate how job parameters can be
* passed into jobs and how state can be maintained
*
* @author Bill Kratzer
*/
public class JobStateExample {
public void run() throws Exception {
Log log = LogFactory.getLog(JobStateExample.class);
log.info("------- Initializing -------------------");
// First we must get a reference to a scheduler
SchedulerFactory sf = new StdSchedulerFactory();
Scheduler sched = sf.getScheduler();
log.info("------- Initialization Complete --------");
log.info("------- Scheduling Jobs ----------------");
// get a "nice round" time a few seconds in the future....
long ts = TriggerUtils.getNextGivenSecondDate(null, 10).getTime();
// job1 will only run 5 times, every 10 seconds
JobDetail job1 = new JobDetail("job1", "group1", ColorJob.class);
SimpleTrigger trigger1 = new SimpleTrigger("trigger1", "group1", "job1", "group1",
new Date(ts), null, 4, 10000);
// pass initialization parameters into the job
job1.getJobDataMap().put(ColorJob.FAVORITE_COLOR, "Green");
job1.getJobDataMap().put(ColorJob.EXECUTION_COUNT, 1);
// schedule the job to run
Date scheduleTime1 = sched.scheduleJob(job1, trigger1);
log.info(job1.getFullName() +
" will run at: " + scheduleTime1 +
" and repeat: " + trigger1.getRepeatCount() +
" times, every " + trigger1.getRepeatInterval() / 1000 + " seconds");
// job2 will also run 5 times, every 10 seconds
JobDetail job2 = new JobDetail("job2", "group1", ColorJob.class);
SimpleTrigger trigger2 = new SimpleTrigger("trigger2", "group1", "job2", "group1",
new Date(ts + 1000), null, 4, 10000);
// pass initialization parameters into the job
// this job has a different favorite color!
job2.getJobDataMap().put(ColorJob.FAVORITE_COLOR, "Red");
job2.getJobDataMap().put(ColorJob.EXECUTION_COUNT, 1);
// schedule the job to run
Date scheduleTime2 = sched.scheduleJob(job2, trigger2);
log.info(job2.getFullName() +
" will run at: " + scheduleTime2 +
" and repeat: " + trigger2.getRepeatCount() +
" times, every " + trigger2.getRepeatInterval() / 1000 + " seconds");
log.info("------- Starting Scheduler ----------------");
// All of the jobs have been added to the scheduler, but none of the jobs
// will run until the scheduler has been started
sched.start();
log.info("------- Started Scheduler -----------------");
log.info("------- Waiting 60 seconds... -------------");
try {
// wait five minutes to show jobs
Thread.sleep(60L * 1000L);
// executing...
} catch (Exception e) {
}
log.info("------- Shutting Down ---------------------");
sched.shutdown(true);
log.info("------- Shutdown Complete -----------------");
SchedulerMetaData metaData = sched.getMetaData();
log.info("Executed " + metaData.numJobsExecuted() + " jobs.");
}
public static void main(String[] args) throws Exception {
JobStateExample example = new JobStateExample();
example.run();
}
}

Java监听器，定时器

猜你喜欢