用Java自定義一個定時器

1.先定義一個監聽類：

import java.util.Date;
import java.util.Timer;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class DemoListener implements ServletContextListener {

    private Timer timer = new Timer();
    
    public void contextDestroyed(ServletContextEvent event) {
        timer.cancel();
    }

    public void contextInitialized(ServletContextEvent event) {
        Date firstTime = new Date(System.currentTimeMillis());
        int period = 5;
        // 設置定時的開始時間和周期
        timer.schedule(new DemoTask(), firstTime, period * 1000);
    }

}

2.制定定時任務類：

import java.net.UnknownHostException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.TimerTask;

import org.dom4j.DocumentException;

public class DemoTask extends TimerTask {
    public void doSomething() throws UnknownHostException, DocumentException, ParseException {
        // 調用動作
        
        
        System.out.println("定時調用動作成功--------------------------------------------------------------------");
    }

    public void run() {
        try {
            doSomething();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

3.web.xml配置監聽類

<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app>
    <display-name>DemoTimer</display-name>
    <listener>
        <listener-class>DemoListener</listener-class>
    </listener>
</web-app>