javaee 使用监听器统计当前在线用户列表-编程知识

在这里插入图片描述
ServletContextListener 和 HttpSessionBindingListener 需要配和使用

TestServletContextListener

package com.yyy.listener;import java.util.ArrayList;
import java.util.List;import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;import com.yyy.po.Users;/*** Application Lifecycle Listener implementation class TestServletContextListener**/
@WebListener
public class TestServletContextListener implements ServletContextListener {/*** Default constructor. */public TestServletContextListener() {// TODO Auto-generated constructor stub}/*** @see ServletContextListener#contextDestroyed(ServletContextEvent)*/public void contextDestroyed(ServletContextEvent arg0)  { // TODO Auto-generated method stubSystem.out.println("服务器关闭了");}/*** @see ServletContextListener#contextInitialized(ServletContextEvent)*/public void contextInitialized(ServletContextEvent arg0)  { // TODO Auto-generated method stub// TODO Auto-generated method stub//初始化数据 变量  数据库连接信息  连接池的信息ServletContext application=  arg0.getServletContext();application.setAttribute("count", 0);//存放所有登录的用户List<Users> onLineUserList=new ArrayList<Users>();application.setAttribute("onLineUserList", onLineUserList);System.out.println("服务器启动了");}}

TestHttpSessionBindingListener

package com.yyy.listener;import java.util.List;import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;import com.yyy.po.Users;/*** Application Lifecycle Listener implementation class TestHttpSessionBindingListener**/
@WebListener
public class TestHttpSessionBindingListener implements HttpSessionBindingListener {private Users user;private List<Users> onLineUserList;/*** Default constructor. */public TestHttpSessionBindingListener() {// TODO Auto-generated constructor stub}public TestHttpSessionBindingListener(Users user) {this.user=user;// TODO Auto-generated constructor stub}public boolean isUserExists(){for(Users myuser:onLineUserList){if(myuser.getUname().equals(user.getUname()))return true;}return false;}public void printUserList(){System.out.println("当前用户列表:");for(Users user:onLineUserList){System.out.println(user.getUname());}}/*** @see HttpSessionBindingListener#valueBound(HttpSessionBindingEvent)*/@Overridepublic void valueBound(HttpSessionBindingEvent arg0)  { // TODO Auto-generated method stub// TODO Auto-generated method stubServletContext application= arg0.getSession().getServletContext();onLineUserList=  (List<Users>) application.getAttribute("onLineUserList");//判断当前用户是否在用户列表中,不存在  则添加到在线列表中		if(!isUserExists()){onLineUserList.add(user);System.out.println("用户:"+user.getUname()+"上线了");//存回到application变量application.setAttribute("onLineUserList", onLineUserList);//打印用户列表printUserList();}}/*** @see HttpSessionBindingListener#valueUnbound(HttpSessionBindingEvent)*/@Overridepublic void valueUnbound(HttpSessionBindingEvent arg0) {// TODO Auto-generated method stubServletContext application= arg0.getSession().getServletContext();if(isUserExists()){onLineUserList.remove(user);System.out.println("用户:"+user.getUname()+"下线了");//存回到application变量application.setAttribute("onLineUserList", onLineUserList);//打印用户列表printUserList();}}}

LoginServlet

package com.yyy.servlet;import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;import com.yyy.listener.TestHttpSessionBindingListener;
import com.yyy.po.Users;
import com.yyy.util.DbHelper;/*** Servlet implementation class LoginServlet*/
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {private static final long serialVersionUID = 1L;/*** @see HttpServlet#HttpServlet()*/public LoginServlet() {super();// TODO Auto-generated constructor stub}/*** @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)*/protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stub//response.getWriter().append("Served at: ").append(request.getContextPath());//获得用户信息String uname=request.getParameter("uname");String pwd=request.getParameter("pwd");//判断是否登录成功String sql="select * from user where uname=? && upwd=?";List<Object> paramList=new ArrayList<Object>();paramList.add(uname);paramList.add(pwd);	DbHelper dbHelper=new DbHelper();List<Map<String, Object>> map=  dbHelper.executeQuery(sql, paramList);if(map!=null && map.size()>0){Users user=new Users();user.setUname(uname);user.setUpwd(pwd);//登录成功//创建一个HttpSessionBindingListener对象用来监听当前用户TestHttpSessionBindingListener httpSessionBingingListener=new TestHttpSessionBindingListener(user);HttpSession session=request.getSession();session.setAttribute("user", httpSessionBingingListener);response.sendRedirect("index.jsp");}elseresponse.getWriter().println("用户名或密码出错");}/*** @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)*/protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubdoGet(request, response);}}