java web 项目中通过session 统计在线访问人数

import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class UserOnlineListener implements HttpSessionListener {
static int count = 0；

@Override
public void sessionCreated(HttpSessionEvent arg0) {
System.out.println(this.getClass().toString()
+ "sessionCreated(HttpSessionEvent arg0)");
count ++;

}

@Override
public void sessionDestroyed(HttpSessionEvent arg0) {
System.out.println(this.getClass().toString()
+ "sessionDestroyed(HttpSessionEvent arg0)");
if(count>0) count --;

}

}

<!-- 监听在线用户 -->
<listener>
<listener-class>
cn.cnic.dep.util.UserOnlineListener
</listener-class>
</listener>

<!-- Session超时定义,单位为分钟 -->
<session-config>
<session-timeout>30</session-timeout>
</session-config>