web.xml中配置：
<listener>
<listener-class>com.mcm.listener.ServletContextListenerImpl</listener-class>
</listener>
<listener>
<listener-class>com.mcm.listener.HttpSessionListenerImpl</listener-class>
</listener>
ServletContextListenerImpl类：
package com.mcm.listener;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class ServletContextListenerImpl implements ServletContextListener {
public void contextDestroyed(ServletContextEvent event) {
ServletContext application = event.getServletContext();
application.removeAttribute("onLineNum");
}
public void contextInitialized(ServletContextEvent event) {
int num = 0;
ServletContext application = event.getServletContext();
application.setAttribute("onLineNum", num);
}
}
HttpSessionListenerImpl类：
package com.mcm.listener;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class HttpSessionListenerImpl implements HttpSessionListener {
public void sessionCreated(HttpSessionEvent event) {
ServletContext application = event.getSession().getServletContext();
Integer num = (Integer) application.getAttribute("onLineNum");
if(num != null){
int count = num;
count = count + 1;
application.setAttribute("onLineNum", count);
}
}
public void sessionDestroyed(HttpSessionEvent event) {
ServletContext application = event.getSession().getServletContext();
Integer num = (Integer) application.getAttribute("onLineNum");
int count = num;
count = count - 1;
application.setAttribute("onLineNum", count);
}
}
index.jsp中：
当前在线人数：${onLineNum }
结果：
