HttpsessionListener 实现在线人数统计

最近在学servlet jsp,用的林信良先生的 jsp&servlet 这本书,在第五章有道在线人数统计的课后题完成,做一次记录.

实际效果:

一:用户类:

package cc.openhome.controler;

public class User {
    private String name;
    private String sessionId;
    private String ip;
    private String firstTime;
    private String userAgent;
    public User(){

    }

    public String getName() {
        return name;
    }

    public String getIp() {
        return ip;
    }

    public String getSessionId() {
        return sessionId;
    }

    public String getFirstTime() {
        return firstTime;
    }

    public String getUserAgent() {
        return userAgent;
    }

    public void setUserAgent(String userAgent) {
        this.userAgent = userAgent;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setFirstTime(String firstTime) {
        this.firstTime = firstTime;
    }

    public void setIp(String ip) {
        this.ip = ip;
    }

    public void setSessionId(String sessionId) {
        this.sessionId = sessionId;
    }

}

二:登录页面:

package cc.openhome.controler;

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 java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.*;

@WebServlet("/login.do")
public class Login extends HttpServlet {

   private ArrayList<User> ulist;
   private Map<String,String> users;
   public Login(){
       users = new HashMap<String,String>();
       users.put("liming","123456");
       users.put("小猪","123456");
       users.put("小林","123456");
   }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        req.setCharacterEncoding("UTF-8");
        String uname = req.getParameter("user");
        String pssd = req.getParameter("pwd");

        String page = "login.html";

        if (users.containsKey(uname) && users.get(uname).equals(pssd)) {
            req.getSession().setAttribute("uname", uname);
            String sessionId = req.getSession().getId();
            ArrayList<User> ulist = (ArrayList<User>) getServletContext().getAttribute("ulist");
            if(ulist == null){
                ulist = new ArrayList<User>();
                getServletContext().setAttribute("ulist",ulist);
            }
            User u = new User();
            u.setSessionId(sessionId);
            u.setName(uname);
            u.setIp(req.getRemoteAddr());
            SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:MM:ss");
            u.setFirstTime(df.format(new Date()));
            u.setUserAgent(req.getHeader("user-agent"));
            ulist.add(u);
            page = "welcome.view";
        }
        resp.sendRedirect(page);
    }
}

三:统计在线人数:

package cc.openhome.controler;

import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.util.List;

@WebListener
public class OnlineUserCounter implements HttpSessionListener {
    private static int counter;

    public static int getCounter(){
        return counter;
    }

    @Override
    public void sessionCreated(HttpSessionEvent se) {
        System.out.println("新建session: "+se.getSession().getId());

    }

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        HttpSession session = se.getSession();
        ServletContext application = session.getServletContext();
        String username = (String) session.getAttribute("username");

        List ulist = (List)
                application.getAttribute("ulist");
        ulist.remove(username);
        System.out.println(username+"已经退出!");

    }
}

四:登录成功页面显示

package cc.openhome.view;

import cc.openhome.controler.User;
import cc.openhome.controler.OnlineUserCounter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

@WebServlet("/welcome.view")
public class Welcome extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        resp.setContentType("text/html;charset=UTF-8");
        PrintWriter out = resp.getWriter();
        HttpSession session = req.getSession(false);
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.01'" +
                "Transitional//EN");
        out.println("<html>");
        out.println("<head>");
        out.println("<title>欢迎</title>");
        out.println("</head>");
        out.println("<body>");

        ArrayList<User> ul = (ArrayList <User>) getServletContext().getAttribute("ulist");
        out.println("<h1> 目前在线人数 "+ ul.size() +"人</h1>");
            Iterator<User> it = ul.iterator();
            while (it.hasNext()){
                User u = it.next();
                out.println("<h4>id: "+ u.getSessionId() +" </h4>");
                out.println("<h4>用户: "+ u.getName()+" </h4>");
                out.println("<h4>ip: "+ u.getIp() +" </h4>");
                out.println("<h4>访问时间: "+ u.getFirstTime() +" </h4>");
                out.println("<h4>浏览器信息: "+ u.getUserAgent() +" </h4>");
                out.println("<br>");
            }

        out.println("</body>");
        out.println("</html>");
        out.close();

        }
}

五:登录的前端页面:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>登录</title>
</head>
<body>
<form action="login.do" method="post">
    用户名: <input type="text" name="user"><br>
    密码:  <input type="password" name="pwd"><br>
    提交: <input type= "submit">
</form>
</body>
</html>

六:实际效果:

七:总结

1.httpsessionListener 工作机制

2,ArrayList 使用

八:不足之处:

1页面展示用的是:在servlet中用的html,还没有学习jsp.

2.已知问题:同一个用户同时登录,重新显示为一新用户,后面再改

参考资料:

http://www.cnblogs.com/shencheng/archive/2011/01/07/1930227.html

https://blog.csdn.net/su20145104009/article/details/53217201

本人菜鸟一枚,如有问题请大神不吝赐教!