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JavaEE Online Number Management System

This blog is a summary of filter, listener, and servlet technologies, which implements simple functions such as displaying the number of online users, detailed information of online users, and the administrator's kick-off function

The detailed code is as follows

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 
 xmlns="http://java.sun.com/xml/ns/javaee" 
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
 http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
 <display-name></display-name> 
 <filter
 <filter-name>character</filter-name>
 <filter-class>cn.hncu.filter.CharacterFilter</filter-class>
 <init-param>
  <param-name>charset</param-name>
  <param-value>utf-8</param-value>
 </init-param>
 </filter>
 <filter
 <filter-name>login</filter-name>
 <filter-class>cn.hncu.filter.LoginFilter</filter-class>
 </filter>
 <filter-mapping>
 <filter-name>character</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>
 <filter-mapping>
 <filter-name>login</filter-name>
 <url-pattern>/servlet/*</url-pattern>
 <url-pattern>/jsps/*</url-pattern>
 <dispatcher>REQUEST</dispatcher>
 <dispatcher>FORWARD</dispatcher>
 </filter-mapping>
 <listener
 <listener-class>cn.hncu.listener.MySessionListener</listener-class>
 </listener>
 <servlet>
 <servlet-name>LoginServlet</servlet-name>
 <servlet-class>cn.hncu.servlet.LoginServlet</servlet-class>
 </servlet>
 <servlet>
 <servlet-name>ShowServlet</servlet-name>
 <servlet-class>cn.hncu.servlet.ShowServlet</servlet-class>
 </servlet>
 <servlet>
 <description>This is the description of my J2EE component</description>
 <display-name>This is the display name of my J2EE component</display-name>
 <servlet-name>KickOutServlet</servlet-name>
 <servlet-class>cn.hncu.servlet.KickOutServlet</servlet-class>
 </servlet>
 <servlet>
 <description>This is the description of my J2EE component</description>
 <display-name>This is the display name of my J2EE component</display-name>
 <servlet-name>LoginOutServlet</servlet-name>
 <servlet-class>cn.hncu.servlet.LoginOutServlet</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>LoginServlet</servlet-name>
 <url-pattern>/LoginServlet</url-pattern>
 </servlet-mapping>
 <servlet-mapping>
 <servlet-name>ShowServlet</servlet-name>
 <url-pattern>/servlet/ShowServlet</url-pattern>
 </servlet-mapping>
 <servlet-mapping>
 <servlet-name>KickOutServlet</servlet-name>
 <url-pattern>/servlet/KickOutServlet</url-pattern>
 </servlet-mapping>
 <servlet-mapping>
 <servlet-name>LoginOutServlet</servlet-name>
 <url-pattern>/servlet/LoginOutServlet</url-pattern>
 </servlet-mapping>
 <welcome-file-list>
 <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>
</web-app>

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
 <title>Online Users Management</title>
 </head>
 <body>
 <h2>Online Users Management</h2>
 <h3>Member Login</h3>
 <c:if test="${ empty sessionScope.user.name}" var="boo">
  <form action='<c:url value="/LoginServlet"></c:url>'>
   Name:<input type="text" name="name"><br/>
    <input type="submit" value="Login"><br/>
  </form>
 </c:if>
 <c:if test="${!boo}" >
  Welcome back,${ sessionScope.user.name}
  <c:if test="${ sessionScope.user.admin}" var="bo">
   Administrator
  </c:if>
  <c:if test="${!bo}" >
   Member
  </c:if>
 </c:if>
 <br/>
  <c:if test="${!boo}" var="boo">
  <a href='<c:url value="/servlet/ShowServlet"/>'>View Online Users</a><br/>
  <a href='<c:url value="/servlet/LoginOutServlet"/>'>Safe Exit</a><br/>
  </c:if>
 </body>
</html>

/jsps/show.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Online User Information</title>
<style type="text/css">
 table {
  color: green;
  border: 1px solid blue;
  border-collapse: collapse;
  width: 500px;
  margin: auto;
 }
 td {
  border: 1px solid blue;
 }
 th {
  border: 1px solid blue;
 }
 body {
  text-align: center;
 }
</style>
 <meta http-equiv="refresh" content="3">
</head>
<body>
 <table>
  <tr>
   <th>Name</th>
   <th>Online Time</th>
   <th>Last Access Time</th>
   <th>ip</th>
   <th>Operation</th>
  </tr>
  <c:forEach items="${requestScope.onlines}" var="online">
  <tr>
   <td>
    <c:if test="${!empty online.user }" var="boo">
      ${online.user.name }
    </c:if>
    <c:if test="${empty online.user }">
      Visitor
    </c:if>
   </td>
   <td>${online.createTime }</td>
   <td>${online.lastAccessedTime }</td>
   <td>${online.ip }</td>
   <td>
    <c:if test="${online.user!=sessionScope.user }"> 
     <c:if test="${!online.user.admin&&boo}">
       <a href='<c:url value="/servlet/KickOutServlet&63;id=${online.id}"/>'Kick out</a>
     </c:if>
    </c:if>
   </td>
  </tr>
  </c:forEach>
 </table>
</body>
</html>

User.java(Object Value)

package cn.hncu.domain;
public class User {
 private String name;
 private boolean admin;
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public boolean isAdmin() {
  return admin;
 }
 public void setAdmin(boolean admin) {
  this.admin = admin;
 }
 @Override
 public String toString() {
  return "User [name=" + name + ", admin=" + admin + "]";
 }
}

MySessionListener.java(Listener)

package cn.hncu.listener;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class MySessionListener implements HttpSessionListener{
 @Override
 public void sessionCreated(HttpSessionEvent se) {
  Map<String, HttpSession> onlines= (Map<String, HttpSession>) se.getSession().getServletContext().getAttribute("onlines");
  if(onlines==null){
   onlines=Collections.synchronizedMap(new HashMap<String, HttpSession>());//Synchronize the lock on the map
   se.getSession().getServletContext().setAttribute("onlines",onlines);
  }
  onlines.put(se.getSession().getId(), se.getSession());
 }
 @Override
 public void sessionDestroyed(HttpSessionEvent se) {
  Map<String, HttpSession> onlines= (Map<String, HttpSession>) se.getSession().getServletContext().getAttribute("onlines");
  if(onlines.containsKey(se.getSession().getId())){
   onlines.remove(se.getSession().getId());
  }
 }
}

CharacterFilter.java(Character filter)}

package cn.hncu.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
public class CharacterFilter implements Filter {
 private String charset;
 @Override
 public void init(FilterConfig filterConfig) throws ServletException {
  charset=filterConfig.getInitParameter("charset");
 }
 @Override
 public void doFilter(ServletRequest request, ServletResponse response,
   FilterChain chain) throws IOException, ServletException {
  request.setCharacterEncoding(charset);
  response.setCharacterEncoding(charset);
  HttpServletRequest req=(HttpServletRequest) request;
  if(req.getSession().getAttribute("ip")==null){
   req.getSession().setAttribute("ip", req.getRemoteAddr());
  }
  chain.doFilter(request, response);
 }
 @Override
 public void destroy() {
 }
}

LoginFilter.java(Prevent tourists from accessing the filter)

package cn.hncu.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginFilter implements Filter {
 @Override
 public void init(FilterConfig filterConfig) throws ServletException {
 }
 @Override
 public void doFilter(ServletRequest request, ServletResponse response,
   FilterChain chain) throws IOException, ServletException {
  HttpServletRequest req=(HttpServletRequest) request;
  if(req.getSession().getAttribute("user")==null){
   ((HttpServletResponse)response).sendRedirect(req.getContextPath())+"/index.jsp");
   return;
  }
  chain.doFilter(request, response);
 }
 @Override
 public void destroy() {
 }
}

LoginServlet.java

package cn.hncu.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import cn.hncu.domain.User;
public class LoginServlet extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  doPost(request, response);
 }
 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  String name = request.getParameter("name");
  User user = (User) request.getSession().getAttribute("user");
  if (user == null && name != null && name.trim().length() > 0) {//Encapsulate User
   user = new User();
   user.setName(name);
   if(name.equals("admin")){
    user.setAdmin(true);
   }
  }
  request.getSession().setAttribute("user", user);
  response.sendRedirect(request.getContextPath())+"/index.jsp");
 }
}

ShowServlet.java

package cn.hncu.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class ShowServlet extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  doPost(request, response);
 }
 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  Map<String, HttpSession> onlines=(Map<String, HttpSession>) request.getServletContext().getAttribute("onlines");
  List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();//Encapsulate Online into list
  if (onlines!=null) {
   Iterator<HttpSession> it = onlines.values().iterator();
   while (it.hasNext()) {
    HttpSession s = it.next();
    Map<String, Object> map = new HashMap<String, Object>();
    map.put("id", s.getId());
    SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss);
    map.put("createTime", sdf.format(new Date(s.getCreationTime())));
    map.put("lastAccessedTime", sdf.format(new Date(s.getLastAccessedTime())) );
    map.put("ip", s.getAttribute("ip"));//ip information is supplemented in characterFilter
    map.put("user", s.getAttribute("user"));
    list.add(map);
   }
  }
  request.setAttribute("onlines", list);
  request.getRequestDispatcher("/jsps/show.jsp()).forward(request, response);
 }
}

KickOutServlet.java

package cn.hncu.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class KickOutServlet extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  doPost(request, response);
 }
 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  String id=request.getParameter("id");
  Map<String, HttpSession> onlines=(Map<String, HttpSession>) request.getServletContext().getAttribute("onlines");
  if (onlines!=null) {
   if (onlines.containsKey(id)) {
    onlines.get(id).invalidate();
   }
  }
  request.getRequestDispatcher("/servlet/ShowServlet()).forward(request, response);
 }
}

LoginOutServlet.java

package cn.hncu.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginOutServlet extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  doPost(request, response);
 }
  public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
   request.getSession().invalidate();
   response.sendRedirect(request.getContextPath())+"/index.jsp");
 }
}

That's all for this article. I hope it will be helpful to everyone's learning and that everyone will support the Yelling Tutorial more.

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