统计当前在线用户数量
1、ServletContext记录个数 package cn.demo.listener; import javax.servlet.ServletContext; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; public class MyServletContextListener implements ServletContextListener { @Override public void contextInitialized(ServletContextEvent sce) { // 容器一启动ServletContext对象就会创建，该方法就会执行 System.out.println("容器创建了..."); ServletContext servletContext = sce.getServletContext(); int count = 0; servletContext.setAttribute("count", count); } @Override public void contextDestroyed(ServletContextEvent sce) { // 容器销毁ServletContext对象就销毁