Understanding WebSockets versus Ajax/REST for Java EE Developers Part II
From Resin 4.0 Wiki
Under Review and under construction...
WebSocket API Chat Room using JSR 356
This is a continuation of the first tutorial in this series (Part 1). In this tutorial, we show how to build a jQuery chat client and a full working, scalable chat server using Resin 4.0.26.
- ChatServlet
- (same as before)
- ChatWebSocketListener
- super simple, just posts ChatMessage to queue for ChatRoom
- ChatRoom
- Uses CDI (Java EE 6 Dependency injection)
- @ApplicationScoped, @Startup,
- manages a collection of ChatClientHandler, sends messages to them
- ChatMessage
- holds Message and WebSocket for current message
- ChatClientHandler
- sits on a writeQueue waiting for messages from queue, 1 Queue per HTML 5 / client
ChatWebSocketListener (* to 1) -> Read Queue (1) -> ChatRoom (1) -> Write Queue (*) -> ChatClientHandler (*)
Only ChatClientHandler uses WebSocketContext to write.
Only ChatWebSocketListener reads from WebSocket.
The ChatRoom responds to three messages, add client, remove client and send message.
void dispatchMessage(ChatMessage message) {
if (message.startsWith("remove client::::")) {
removeClient(clientId);
} else if (message.startsWith("send message::::")) {
doSendMessage(clientId, payload);
} else if (message.startsWith("add client::::")) {
launchNewClient(chatMessage, clientId);
}
Resin 4.0.27 and 4.0.28 should have some enhancements to further ease WebSocket development.
Registering WebSocket Protocol
ChatServlet.java
package com.caucho.websocket.example;
import java.io.IOException;
import java.util.concurrent.ExecutorService;
import javax.inject.Inject;
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.caucho.websocket.WebSocketServletRequest;
/**
* Servlet implementation class ChatServlet
*/
@WebServlet("/chat")
public class ChatServlet extends HttpServlet {
@Inject ChatRoom chatRoom;
@Inject ExecutorService executor;
/**
* Handle Websocket handshake.
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String protocol = request.getHeader("Sec-WebSocket-Protocol");
System.out.println("___________ doGet MEHTOD ________________ " + protocol);
if ("caucho-example-chat-protocol".equals(protocol)) {
System.out.println("___________ WEBSOCKET Handshake ________________ " + protocol);
response.setHeader("Sec-WebSocket-Protocol", "caucho-example-chat-protocol");
WebSocketServletRequest wsRequest = (WebSocketServletRequest) request;
wsRequest.startWebSocket(new ChatWebSocketListener(chatRoom));
}
}
}
WebSocketListener, delegating to queues
ChatWebSocketListener.java
package com.caucho.websocket.example;
import java.io.IOException;
import java.io.Reader;
import com.caucho.websocket.WebSocketContext;
import com.caucho.websocket.AbstractWebSocketListener;
public class ChatWebSocketListener extends AbstractWebSocketListener {
volatile boolean close;
ChatRoom chatRoom;
public ChatWebSocketListener(ChatRoom chatRoom) {
this.chatRoom = chatRoom;
}
@Override
public void onReadText(WebSocketContext context, Reader reader)
throws IOException {
System.out.println("___________ onReadText ________________ " );
char [] data = new char[4096];
reader.read(data);
String message = new String(data).trim();
System.out.println("ChatWebSocketListener::::" + message );
chatRoom.sendMessage(new ChatMessage(message, context));
}
@Override
public void onDisconnect(WebSocketContext context) throws IOException {
close=true;
}
}
Chat Room, handling message coordination
ChatRoom.java
package com.caucho.websocket.example;
import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executor;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import javax.ejb.Startup;
import javax.enterprise.context.ApplicationScoped;
@ApplicationScoped
@Startup
public class ChatRoom {
Map<String, ChatClientHandler> chatClients = new HashMap<String, ChatClientHandler>();
BlockingQueue<ChatMessage> readQueue = new ArrayBlockingQueue<ChatMessage>(2000);
Executor executor;
public ChatRoom() {
executor = new ThreadPoolExecutor(10, 20, 90, TimeUnit.SECONDS,
new ArrayBlockingQueue<Runnable>(1));
(new Thread(new Runnable() {
public void run() {
ChatRoom.this.run();
}
})).start();
}
private void run() {
while (true) {
try {
ChatMessage message = readQueue.poll(500, TimeUnit.MILLISECONDS);
if (message != null) {
dispatchMessage(message);
}
} catch (InterruptedException e) {
break;
}
}
}
private void launchNewClient(ChatMessage message, String client) {
System.out.println("launchNewClient::::" + client);
ChatClientHandler chatClientHandler = new ChatClientHandler(message.getContext(), client);
chatClients.put(chatClientHandler.getName(), chatClientHandler);
executor.execute(chatClientHandler);
doSendMessage(chatClientHandler.getName(), chatClientHandler.getName() + " has join the chat room");
}
private void dispatchMessage(ChatMessage message) {
String strMessage = message.getMessage();
String[] strings = strMessage.split("::::");
String clientId = strings[1];
if (strMessage.startsWith("remove client::::")) {
removeClient(clientId);
} else if (strMessage.startsWith("send message::::")) {
doSendMessage(clientId, strings[2]);
} else if (strMessage.startsWith("add client::::")) {
launchNewClient(message, clientId);
}
else {
System.err.println("ACK... Don't understand your message!!!!! " + message);
}
}
private void doSendMessage(String client, String message) {
String sendMessage = String.format("%s : %s", client, message);
System.out.printf("sendMessage::Sending message %s\n", sendMessage );
Iterator<ChatClientHandler> iterator = chatClients.values().iterator();
while (iterator.hasNext()) {
ChatClientHandler chatClientHandler = iterator.next();
if (client.equals(chatClientHandler.getName())) //comment this if you don't want to echo back messages
continue;
if (chatClientHandler.isError()) {
iterator.remove();
try {
chatClientHandler.close();
} catch (IOException e) {
}
continue;
}
if (!chatClientHandler.isAlive()) { //Could be kicked out of executor pool. Kick it back in.
try {
executor.execute(chatClientHandler);
} catch (RejectedExecutionException ree) {
iterator.remove();
}
continue;
}
System.out.printf("sendMessage::Sending message %s to %s\n", sendMessage, chatClientHandler.getName() );
chatClientHandler.sendMessage(sendMessage);
}
}
private void removeClient(String client) {
System.out.println("removeClient::::[" + client + "]::::");
ChatClientHandler chatClientHandler = chatClients.get(client);
if (chatClientHandler != null) {
System.out.println("removeClient:::: found " + client + " to remove.");
doSendMessage(chatClientHandler.getName(), chatClientHandler.getName() + " has become bored with this chat room");
chatClients.remove(client);
try {
chatClientHandler.close();
} catch (IOException e) {
}
}
}
public void sendMessage(ChatMessage message) {
try {
readQueue.offer(message, 100, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
throw new IllegalStateException ("Unable to add message to queue");
}
}
}
ChatMessage.java
package com.caucho.websocket.example;
import com.caucho.websocket.WebSocketContext;
public class ChatMessage {
String message;
WebSocketContext context;
public ChatMessage(String message, WebSocketContext context) {
this.message = message;
this.context = context;
}
public final String getMessage() {
return message;
}
public final WebSocketContext getContext() {
return context;
}
}
Managing the outgoing WebSocket streams
ChatClientHandler.java
package com.caucho.websocket.example;
import java.io.Closeable;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import com.caucho.websocket.WebSocketContext;
/**
* ChatClientHandler handles queued messages that are going to the client.
* @author r hightower
*
*/
public class ChatClientHandler implements Runnable, Closeable{
/** Name of the client. */
String name;
/** WebSocketContext to send messages to the browser client.*/
WebSocketContext context;
/** Queue that ChatClientHandler are monitoring. When a message comes in on this queue, ChatClientHandler sends it.*/
BlockingQueue<String> writeQueue = new ArrayBlockingQueue<String>(2000);
/** Keeps track if the thread for this ChatClientHandler is alive. */
volatile boolean alive;
/** Keeps track if their has been an error sending the message so the ChatRoom can clean it up. */
volatile boolean error;
/** The reason for the error */
String reason;
/** Flag to indicate whether we should close or not. */
volatile boolean close;
public ChatClientHandler(WebSocketContext context, String name) {
this.context = context;
this.name = name;
}
/** Chat room calls this method to send a message. */
public void sendMessage(String sendMessage) {
System.out.println("ChatClientHandler::::" + sendMessage);
this.writeQueue.offer(sendMessage);
}
@Override
public void run() {
alive = true;
reason = "";
while (true) {
try {
if (Thread.currentThread().isInterrupted()) {
alive=false;
break;
}
if (close) {
break;
}
/* Get a message, send a message to client if not null. */
String message = writeQueue.poll(1000, TimeUnit.SECONDS);
if (message!=null) {
System.out.printf("ChatClientHandler::::run loop::::SENDING MESSAGE %s to %s\n", message, name);
PrintWriter out = context.startTextMessage();
out.print(message);
out.close(); //Close sends the message to browser.
}
} catch (InterruptedException e) {
alive = false; //Our thread is interrupted. We can be resumed.
break;
} catch (IOException e) {
alive = false;
error = true;
reason = e.getMessage();
e.printStackTrace();
break;
}
}
}
public String getName() {
return name;
}
public boolean isAlive() {
return alive;
}
public boolean isError() {
return error;
}
public String getReason() {
return reason;
}
@Override
public void close() throws IOException {
close = true;
if (context!=null) {
if (error) {
context.disconnect();
} else {
context.close();
}
}
}
}
Simple JavaScript clients that use WebSocket to send messages to chat
rick.html
<html>
<head>
<title>RICK TEST CLIENT</title>
<script language="javascript" type="text/javascript">
/* http://dev.w3.org/html5/websockets/ */
var socket = null;
function sendChatMessage() {
document.getElementById("span_result").innerHTML = "";
socket.send("send message::::Rick Hightower::::Hi Bob");
}
function handleChatMessageWebSocketResponse(msg) {
document.getElementById("span_result").innerHTML = msg.data;
}
function initSocket() {
if (socket == null) {
socket = new WebSocket("ws://localhost:8080/web-socket-example/chat", "caucho-example-chat-protocol");
socket.onmessage = handleChatMessageWebSocketResponse;
}
socket.onerror = function(msg) {
document.getElementById("error_result").innerHTML = "ERROR:" + msg;
}
socket.onopen = function() {
document.getElementById("span_result").innerHTML = "Socket Status: "
+ socket.readyState + " (open)";
}
socket.onclose = function() {
document.getElementById("span_result").innerHTML = "Socket Status: "
+ socket.readyState + " (Closed)";
}
}
initSocket();
function connectRick() {
document.getElementById("span_result").innerHTML = "CONNECT RICK";
socket.send("add client::::Rick Hightower");
}
function clearSend() {
document.getElementById("span_result").innerHTML = "";
}
function disconnectRick() {
document.getElementById("span_result").innerHTML = "CONNECT RICK";
socket.send("remove client:::Rick Hightower");
}
</script>
</head>
<body>
<h1>RICK TEST CHAT</h1>
<br />
<a href="javascript:connectRick();">CONNECT RICK</a>
<br />
<a href="javascript:sendChatMessage();">Send Hi Bob</a>
<br />
<a href="javascript:disconnectRick();">DISCONNECT RICK</a>
<br />
<a href="javascript:clearSend();">Clear send results</a>
<br />
<span id="span_result"></span>
<span id="error_result"></span>
</body>
</html>
bob.html
<html>
<head>
<title>BOB TEST CLIENT</title>
<script language="javascript" type="text/javascript">
/* http://dev.w3.org/html5/websockets/ */
var socket = null;
function sendChatMessage() {
document.getElementById("span_result").innerHTML = "";
socket.send("send message::::Bob Deanna::::Hi Rick");
}
function handleChatMessageWebSocketResponse(msg) {
document.getElementById("span_result").innerHTML = msg.data;
}
function initSocket() {
if (socket == null) {
socket = new WebSocket("ws://localhost:8080/web-socket-example/chat", "caucho-example-chat-protocol");
socket.onmessage = handleChatMessageWebSocketResponse;
}
socket.onerror = function(msg) {
document.getElementById("error_result").innerHTML = "ERROR:" + msg;
}
socket.onopen = function() {
document.getElementById("span_result").innerHTML = "Socket Status: "
+ socket.readyState + " (open)";
}
socket.onclose = function() {
document.getElementById("span_result").innerHTML = "Socket Status: "
+ socket.readyState + " (Closed)";
}
}
initSocket();
function connectBob() {
document.getElementById("span_result").innerHTML = "CONNECT BOB";
socket.send("add client::::Bob Deanna");
}
function clearSend() {
document.getElementById("span_result").innerHTML = "";
}
function disconnectBob() {
document.getElementById("span_result").innerHTML = "CONNECT BOB";
socket.send("remove client::::Bob Deanna");
}
</script>
</head>
<body>
<h1>BOB TEST CHAT</h1>
<br />
<a href="javascript:connectBob();">CONNECT BOB</a>
<br />
<a href="javascript:sendChatMessage();">Send Hi Rick</a>
<br />
<a href="javascript:disconnectBob();">DISCONNECT BOB</a>
<br />
<a href="javascript:clearSend();">Clear send results</a>
<br />
<span id="span_result"></span>
<span id="error_result"></span>
</body>
</html>
Creating a jQuery prototype to get the user interactions down
chat_proto_no_web_socket.html
<html>
<head>
<title>Chat Client</title>
<link rel="stylesheet" type="text/css" href="css/style.css" media="screen" />
<script type="text/javascript" src="scripts/jquery-1.7.1.js"></script>
<script type="text/javascript">
var ENTER_KEY = '13';
var chatUserSession = {"version":"1.0"};
function chat_Login () {
chatUserSession.userName = $("#userName").val();
$("#loginDiv").hide(500);
$('#header').text("Chat Client (logging in...) : " + chatUserSession.userName);
$('#statusBarPara1').text(chatUserSession.userName + " is logging in...");
$("#inputArea").show(500);
$("#statusBar").show(500);
$("#chatInput").focus();
}
$(document).ready(function() {
$("#inputArea").hide();
$("#userName").focus();
$("#statusBar").css("border", "1 px solid black");
$("#statusBar").click(function(){
$("#statusBar").hide(300);
});
$("#chatInput").keypress(function(event) {
var keycode = (event.keyCode ? event.keyCode : event.which);
if(keycode == ENTER_KEY){
var textMessage = $("#chatInput").val();
$("#chatInput").val("");
$("#hint").hide(500);
$("#chatHistory").prepend("<p>" + textMessage + "</p>");
}
event.stopPropagation();
});
$("#login").click(function(event) {
chat_Login();
event.stopPropagation();
});
$("#userName").keypress(function(event) {
var keycode = (event.keyCode ? event.keyCode : event.which);
if(keycode == ENTER_KEY){
chat_Login();
event.stopPropagation();
}
});
});
</script>
</head>
<body>
<h1 id="header">Chat Client</h1>
<div id="statusBar">
<p id="statusBarPara1">Welcome to Chat App, Click to hide</p>
</div>
<div id="loginDiv">
User name <input id="userName" type="text" /> <input id="login" type="submit" value="Login" />
</div>
<div id="inputArea">
<p id="hint">Type your message here and then hit return</p>
<input id="chatInput" type="text" value="" />
</div>
<div id="chatHistoryDiv">
<p id="chatHistory"></p>
</div>
</body>
</html>
Creating a jQuery and WebSocket full featured chat application
chat.html (Uses full websocket API)
<html>
<head>
<title>Chat Client</title>
<link rel="stylesheet" type="text/css" href="css/style.css"
media="screen" />
<script type="text/javascript" src="scripts/jquery-1.7.1.js"></script>
<script type="text/javascript">
var ENTER_KEY = '13';
var TOKEN_DELIM = "::::";
function buildWebSocketURL() {
var url = document.URL;
var parts = url.split('/');
var scheme = parts[0];
var hostPort = parts[2];
var wssScheme = null;
if (scheme=="http:") {
wssScheme="ws:";
} else if (scheme=="https:") {
wssScheme="wss:";
}
wssUrl = wssScheme + "//" + hostPort + "/web-socket-example/chat";
return wssUrl;
}
var chatUserSession = {
version : "1.0",
webSocketProtocol : "caucho-example-chat-protocol",
webSocketURL : buildWebSocketURL(),
webSocket : null,//WebSocket
userName : null
};
function chat_sendMessage(message) {
$("#chatHistory").prepend("<p style='color:green'> ME : " + message + "</p>");
chatUserSession.webSocket.send("send message" + TOKEN_DELIM
+ chatUserSession.userName + TOKEN_DELIM + message);
}
function chat_joinChat() {
chatUserSession.webSocket.send("add client" + TOKEN_DELIM
+ chatUserSession.userName);
}
function chat_leaveChat() {
chatUserSession.status(chatUserSession.userName + " is leaving chat");
chatUserSession.webSocket.send("remove client" + TOKEN_DELIM
+ chatUserSession.userName);
}
function chat_openWebSocket() {
chatUserSession.webSocket = new WebSocket(chatUserSession.webSocketURL,
chatUserSession.webSocketProtocol);
var socket = chatUserSession.webSocket;
socket.onmessage = function(msg) {
chatUserSession.onMessage(msg);
}
socket.onerror = function(errorEvent) {
chatUserSession.onError(errorEvent);
}
socket.onopen = function() {
chatUserSession.onOpen();
}
socket.onclose = function(closeEvent) {
chatUserSession.onClose(closeEvent);
}
}
function chat_onMessage(msgEvent) {
chatUserSession.status("New Message :" + msgEvent.data);
$("#chatHistory").prepend("<p style='color:blue'>" + msgEvent.data + "</p>");
}
function chat_Login() {
chatUserSession.userName = $("#userName").val();
$("#loginDiv").hide(500);
$('#header').text(
"Chat Client (logging in...) : " + chatUserSession.userName);
chatUserSession.status(chatUserSession.userName + " is logging in...");
chatUserSession.open();
}
function chat_onOpen() {
chatUserSession.joinChat();
chatUserSession.status("Chat Client (logged in) : " + chatUserSession.userName);
$('#header').text(
"Chat Client (logged in...) : " + chatUserSession.userName);
$("#inputArea").show(500);
$("#statusBar").show(500);
$("#chatInput").focus();
}
function chat_Status(message) {
$('#statusBarPara1').text(message);
$("#statusBar").show(500);
}
function chat_onClose(closeEvent) {
$("#loginDiv").show(500);
$('#header').text(
"Chat Client (not connected) : " + chatUserSession.userName);
$('#statusBarPara1').text(chatUserSession.userName + " not logged in. " +
":: Reason: " + closeEvent.reason +
" Code: " + closeEvent.code);
$("#inputArea").hide(500);
$("#statusBar").show(500);
$("#userName").val(chatUserSession.userName);
$("#userName").focus();
}
function chat_onError(msg) {
$('#statusBarPara1').text(" Websocket error :" + JSON.stringfy(msg));
$("#statusBar").show(500);
}
chatUserSession.open = chat_openWebSocket;
chatUserSession.onMessage = chat_onMessage;
chatUserSession.onOpen = chat_onOpen;
chatUserSession.login = chat_Login;
chatUserSession.onClose = chat_onClose;
chatUserSession.onError = chat_onError;
chatUserSession.joinChat = chat_joinChat;
chatUserSession.sendMessage = chat_sendMessage;
chatUserSession.leaveChat = chat_leaveChat;
chatUserSession.status = chat_Status;
$(document).ready(function() {
$("#inputArea").hide();
$("#userName").focus();
$("#statusBar").click(function() {
$("#statusBar").hide(300);
});
$("#chatInput").keypress(function(event) {
var keycode = (event.keyCode ? event.keyCode : event.which);
if (keycode == ENTER_KEY) {
var textMessage = $("#chatInput").val();
if (textMessage=="bye!") {
chatUserSession.leaveChat();
} else {
$("#chatInput").val("");
$("#hint").hide(500);
chatUserSession.sendMessage(textMessage);
}
}
event.stopPropagation();
});
$("#login").click(function(event) {
chatUserSession.login();
event.stopPropagation();
});
$("#userName").keypress(function(event) {
var keycode = (event.keyCode ? event.keyCode : event.which);
if (keycode == ENTER_KEY) {
chatUserSession.login()
event.stopPropagation();
}
});
});
</script>
</head>
<body>
<h1 id="header">Chat Client</h1>
<div id="statusBar">
<p id="statusBarPara1">Welcome to Chat App, Click to hide</p>
</div>
<div id="loginDiv">
User name <input id="userName" type="text" /> <input
id="login" type="submit" value="Login" />
</div>
<div id="inputArea">
<p id="hint">Type your message here and then hit return (entering in 'bye!' logs out)</p>
<input id="chatInput" type="text" value="" />
</div>
<div id="chatHistoryDiv">
<p id="chatHistory"></p>
</div>
</body>
</html>
