unable to send notifications to a specific loggedin user using servlet 3.0 and spring mvc 3.0. gson

[Zia Ul Mustafa]

I made an application and i can send the message/notification to all loggedin users immediately. But the problem is that i am unable to send notifications to a specific user; as an example facebook chat.

I am using Servlets 3.0, Spring MVC 3.0, GSon and AJAX Jquery.

Here is my code:

web.xml

<web-app id="WebApp_ID" version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

<display-name>Spring Web MVC Application</display-name>

<servlet>
    <servlet-name>mvc-dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>
<servlet>
    <description>
    </description>
    <display-name>ChatServlet</display-name>
    <servlet-name>ChatServlet</servlet-name>
    <servlet-class>com.servlet.ChatServlet</servlet-class>
</servlet>


<servlet-mapping>
    <servlet-name>mvc-dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>
<servlet-mapping>
    <servlet-name>ChatServlet</servlet-name>
    <url-pattern>/ChatServlet</url-pattern>
</servlet-mapping>


<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/mvc-dispatcher-servlet.xml</param-value>
</context-param>

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

</web-app>

CONTROLLER

package com.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class HelloController {

@RequestMapping(value="/welcome", method = RequestMethod.GET)
public String printWelcome(ModelMap model) {

    model.addAttribute("message", "Spring 3 MVC Hello World");
    return "hello";
}

@RequestMapping(value="/", method = RequestMethod.GET)
public String chatServlet(ModelMap model) {

    return "index";
}

}

SERVLET

package com.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;




/**
 * Servlet implementation class ChatServlet
 */
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.LinkedBlockingQueue;

import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.ServletConfig;
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 com.google.gson.Gson;

@WebServlet(urlPatterns = "/chat", asyncSupported = true)
public class ChatServlet extends HttpServlet {

    private static final long serialVersionUID = -277914015930424042L;

    private Map<String, AsyncContext> asyncContexts = new ConcurrentHashMap<String, AsyncContext>();
    private BlockingQueue<String> messages = new LinkedBlockingQueue<String>();
    private Thread notifier = new Thread(new Runnable() {
            public void run() {
                    while (true) {
                            try {
                                    // Waits until a message arrives
                                    String message = messages.take();

                                    // Sends the message to all the AsyncContext's response
                                    for (AsyncContext asyncContext : asyncContexts.values()) {
                                            try {

                                                    sendMessage(asyncContext.getResponse().getWriter(), message);
                                            } catch (Exception e) {
                                                    asyncContexts.values().remove(asyncContext);
                                            }
                                    }
                            } catch (InterruptedException e) {
                                    break;
                            }
                    }
            }
    });

    private void sendMessage(PrintWriter writer, String message) throws IOException {
            // default message format is message-size ; message-data ;
            writer.print(message.length());
            writer.print(";");
            writer.print(message);
            writer.print(";");
            writer.flush();
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
    }

    @Override
    public void init(ServletConfig config) throws ServletException {
            super.init(config);
            notifier.start();
    }

    // GET method is used to establish a stream connection
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
                    throws ServletException, IOException {

            // Content-Type header
            response.setContentType("text/plain");
            response.setCharacterEncoding("utf-8");

            // Access-Control-Allow-Origin header
            response.setHeader("Access-Control-Allow-Origin", "*");

            PrintWriter writer = response.getWriter();

            // Id
            final String id = UUID.randomUUID().toString();
            writer.print(id);
            writer.print(';');

            // Padding
            for (int i = 0; i < 1024; i++) {
                    writer.print(' ');
            }
            writer.print(';');
            writer.flush();

            final AsyncContext ac = request.startAsync();
            ac.addListener(new AsyncListener() {
                    public void onComplete(AsyncEvent event) throws IOException {
                            asyncContexts.remove(id);
                    }

                    public void onTimeout(AsyncEvent event) throws IOException {
                            asyncContexts.remove(id);
                    }

                    public void onError(AsyncEvent event) throws IOException {
                            asyncContexts.remove(id);
                    }

                    public void onStartAsync(AsyncEvent event) throws IOException {

                    }

            });
            asyncContexts.put(id, ac);
    }

    // POST method is used to communicate with the server
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
                    throws ServletException, IOException {
            request.setCharacterEncoding("utf-8");

            AsyncContext ac = asyncContexts.get(request.getParameter("metadata.id"));
            if (ac == null) {
                    return;
            }

            // close-request
            if ("close".equals(request.getParameter("metadata.type"))) {
                    ac.complete();
                    return;
            }

            // send-request
            Date date = new Date();

            Map<String, String> data = new LinkedHashMap<String, String>();

                data.put("username", request.getParameter("username"));
                data.put("message", request.getParameter("message"));

            try {
                    messages.put(new Gson().toJson(data));
            } catch (InterruptedException e) {
                    throw new IOException(e);
            }
    }

    @Override
    public void destroy() {
            messages.clear();
            asyncContexts.clear();
            notifier.interrupt();
    }

}

INDEX.JSP

<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>

<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE html>
<html>
    <head>
            <title>MVC - Servlet 3</title>
            <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

            <script src="<c:url value="/resources/js/jquery-1.5.0.js" />"></script>
            <script src="<c:url value="/resources/js/jquery.stream-1.2.js" />"></script>

<!--                 <script type="text/javascript" src="/WEB-INF/js/jquery-1.5.0.js"></script> -->
<!--                 <script type="text/javascript" src="/WEB-INF/js/jquery.stream-1.2.js"></script> -->
  <script type="text/javascript">
            $.stream.setup({enableXDR: true});
            var chat = {
                    lastUsername: "Servlet Date Example in MVC", 
                    username: $.trim(window.prompt("Username?")) || "Anonymous" + $(window).width()
            };

            var date = new Date();
            $(function() {
                    $.stream("chat", {
                            type: "http",
                            dataType: "json",
                            context: $("#content")[0],
                            open: function(event, stream) {
//                                         $("#editor .message").removeAttr("disabled").focus();
                                    stream.send({username: chat.username, message: date.toTimeString()});
                            },
                            message: function(event) {
                                    if (chat.lastUsername !== event.data.username) {
                                            $("<p />").addClass("user").text(chat.lastUsername = event.data.username).appendTo(this);
                                    }

                                    $("<p />").addClass("message").text(event.data.message).appendTo(this);
                                    this.scrollTop = this.scrollHeight;
                            },
//                                 error: function() {
//                                         $("#editor .message").attr("disabled", "disabled");
//                                 },
//                                 close: function() {
//                                         $("#editor .message").attr("disabled", "disabled");
//                                 }
                    });

//                         $("#editor .user").text(chat.username);
//                         $("#editor .message").keyup(function(event) {
//                                 if (event.which === 13 &&                    $.trim(this.value)) {
//                                         $.stream().send({username: chat.username, message: this.value});
//                                         this.value = "";
//                                 }
//                         });

                    $(window).resize(function() {
//                                 var content =     $("#content").height($(window).height() - $("#editor").outerHeight(true) - 15)[0];
                            var content = $("#content").height($(window).height());
                            content.scrollTop = content.scrollHeight;
                    }).resize();
            });
            </script>
            <style>
            body {padding: 0; margin: 0; min-width: 320px; font-family: 'Trebuchet MS','Malgun Gothic',Verdana,Helvetica,Arial,sans-serif; font-size: 62.5%; color: #333333}
            .content {height: 100%; overflow-y: auto; padding: 14px 15px 0 25px;}
            .content p {margin: 0; padding: 0;}
            .content .user {font-size: 1.8em; color: #3e3e3e; font-weight: bold; letter-spacing: -1px; margin-top: 0.5em;}
            .content .message {font-size: 1.3em; color: #444444; line-    height: 1.7em; word-wrap: break-word;}
/*                 .editor {margin: 0 25px 15px 25px;} */
/*                 .editor .user {font-size: 1.5em; display: inline-block; margin: 1em;} */
/*                 .editor input {font-family: 'Trebuchet MS','Malgun Gothic',Verdana,Helvetica,Arial,sans-serif;} */
/*                 .editor .message {width: 100%; height: 28px; line-height: 28px; border: medium none; border-color: #E5E5E5 #DBDBDB #D2D2D2; border-style: solid; border-width: 1px;} */
            </style>
    </head>
    <body>
            <div id="content" class="content">
                    <p class="user"><span>Welcome</span></p>
                    <p class="message"></p>
            </div>
<!--                 <div id="editor" class="editor"> -->
<!--                         <p class="user"></p> -->
<!--                         <form action="#" onsubmit="return false;"> -->
<!--                                 <input class="message" type="text" disabled="disabled" /> -->
<!--                         </form> -->
<!--                 </div> -->
    </body>
</html>

I am working on a live project; that's why I am in hurry to find accurate solution. Thanks in advance. Please help me waiting for solution.