HttpSessionListener实现session定时扫描仪

package cn.lfd.web.listener;

import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Timer;
import java.util.TimerTask;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
/*
* session定时扫描仪
*/
public class SessionScanerListener implements HttpSessionListener,ServletContextListener {
private List<HttpSession> list = Collections.synchronizedList(new LinkedList<HttpSession>());//定义好装HttpSession的集合
private Object lock = new Object();//锁
@Override
public void contextInitialized(ServletContextEvent sce) {
Timer timer = new Timer();
timer.schedule(new MyTask(list,lock), 0, 1000*60);//计时器 一分钟扫描一下session
}

@Override
public void sessionCreated(HttpSessionEvent se) {
HttpSession session = se.getSession();
synchronized (lock) {
list.add(session);//session一被创建就加到集合中
}

System.out.println("创建");
}

@Override
public void sessionDestroyed(HttpSessionEvent se) {
System.out.println("摧毁");

}

@Override
public void contextDestroyed(ServletContextEvent sce) {
// TODO Auto-generated method stub

}
}

class MyTask extends TimerTask{//要定时执行的任务
private List<HttpSession> list;
private Object lock;

MyTask(List<HttpSession> list,Object lock) {
this.list = list;
this.lock = lock;
}
@Override
public void run() {
synchronized (lock) {//使list集合在添加的时候不会执行删除，解决并发问题
ListIterator<HttpSession> it = list.listIterator();
while(it.hasNext()) {
HttpSession session = (HttpSession) it.next();
if(System.currentTimeMillis()-session.getLastAccessedTime()>=1000*60) {//判断session多久没有使用
session.invalidate();//一分钟没有使用的session自动摧毁,减轻系统压力
it.remove();
}
}
}
}
}