Stateful HelloWorld

Let us make HellowWorld 'stateful' - i.e. make it maintain some data ("state") between requests.

We will store the exact time a request is received. If the next request is received later than a certain threshold, we can potentially timeout the session. Many websites do this for security.

In this example, we will not actually timeout - we just want to demonstrate how to maintain 'state'.

We will maintain a simple Hashtable which maps the user ID (that we get from the cookie) to the time the request is received.

Here is what HelloWorld looks like now:

 package org.confucius;  
   
 import java.io.IOException;  
 import java.util.Date;  
 import java.util.HashMap;  
 import javax.servlet.ServletException;  
 import javax.servlet.http.Cookie;  
 import javax.servlet.http.HttpServlet;  
 import javax.servlet.http.HttpServletRequest;  
 import javax.servlet.http.HttpServletResponse;  
   
 public class HelloWorld extends HttpServlet {  
      private static int nextUserId = 0;  
      private static HashMap<String, Date> requestsTracker = new HashMap<String, Date>();  
   
      public void doGet(HttpServletRequest request, HttpServletResponse response)  
                throws ServletException, IOException {  
           String cookieValue = getCookieValue(request.getCookies(), "userId");  
   
           if (cookieValue == null) {  
                cookieValue = String.valueOf(nextUserId);  
                Cookie userCookie = new Cookie("userId", cookieValue);  
                response.addCookie(userCookie);  
                nextUserId++;  
           }  
   
           Date now = new Date();  
           response.getWriter().write(  
                     "Your last request was received on: "  
                               + requestsTracker.get(cookieValue) + ", updating to: "  
                               + now);  
           requestsTracker.put(cookieValue, now);  
      }  
   
      private String getCookieValue(Cookie[] cookies, String cookieName) {  
           if (cookies == null)  
                return null;  
   
           for (int i = 0; i < cookies.length; i++) {  
                Cookie cookie = cookies[i];  
                if (cookieName.equals(cookie.getName()))  
                     return (cookie.getValue());  
           }  
           return null;  
      }  
 }  

Build HelloWorld.war, deploy it, then point your browser to:
http://localhost:8080/HelloWorld/home

Each time you refresh the browser, you will see the time that the last request was received.