Web Sockets lecture under the series of Java Enterprise Edition lectures delivered at ECE Paris.

1. JEE - WebSockets
Fahad R. Golra
ECE Paris Ecole d'Ingénieurs - FRANCE

2. Lecture 6 - WebSockets
• Web communications technologies
• Web Socket methodology
• Web Socket APIs
• JavaScript API
• Java API for WebSockets
2 JEE - WebSockets

3. Interactions over HTTP
• It is half-duplex
• It is verbose
• Server push issue
• Frequent Polling
• Long Polling
• Chunked Encoding
• Applet & Flash
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4. Frequent polling
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5. Long Polling
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6. Chunked Encoding
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7. Applets & Adobe Flash
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8. Interactions through WebSockets
• It is TCP-based
• Supports bi-directional, full-duplex messaging
• Two phases
• Handshake
• Data Transfer
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9. Handshake
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client Server
• Agreeing on upgrade to WebSocket
• No response means no handshake
Handshake Request (over HTTP)
Handshake Response (over HTTP)

10. WebSocket Upgrade Request
GET /webSocketEndpoint HTTP/1.1
Host: www.ece.fr
Connection: Upgrade
Upgrade: websocket
Origin: http://ece.fr
Sec-WebSocket-Key: s3JKEMbDL4ErLkh9GBlXDx==
Sec-WebSocket-Version: 13
Sec-WebSocket-Protocol: chat
HTTP/1.1 101 Switching Protocols
Server: Apache 2.4
Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Accept: HSmrc0sMlYUkAGmm5OPpG2HaGWk=
Sec-WebSocket-Protocol: chat
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client key
hashed value
Server

11. Establishing a connection
• Once connected both client and server become peers
with equal rights for interaction and closing the
session.
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client Server
Handshake Request (over HTTP)
Handshake Response (over HTTP)
Connected

12. Full-duplex WebSocket Communications
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client Server
message
Connected
message
message
message
message
message
Disconnected
close

13. Where is it used?
• Chat
• Online games
• Live stock/News tickers
• HD Video Streaming
• Bulk transactional data transfer
• Real time monitoring for remote systems
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14. WebSocket Interface in API
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15. APIs for WebSocket
• Javascript API
• Client Only
var connection = new WebSocket(uri);
• JEE
• Client API
• foundational API for data transfer
• Server API
• additional constructs for managing handshakes,
server endpoints, server container, etc.
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16. Javascript API - readyState Attribute
• CONNECTING (numeric value 0)
• When object is created. The connection has not yet established.
• OPEN (numeric value 1)
• The WebSocket connection is established and communication is
possible.
• CLOSING (numeric value 2)
• The connection is going through the closing handshake, or the
close() method has been invoked.
• CLOSED (numeric value 3)
• The connection has been closed or could not be opened.
if(connection.readyState == WebSocket.OPEN) {
/* do something */ }
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17. Javascript API - events
connection.onopen = function(event) { }
• readyState changes from CONNECTING to OPEN
connection.onclose = function(event) { }
• readyState changes from CLOSING to CLOSED
connection.onerror = function(event) { }
• In case of client-side errors
connection.onmessage = function(event) { }
• On arrival of a message
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18. JavaScriptAPI - onmessage()
• It has a data property
• String: message = text
• Blob: message = binary, binaryType = “blob”
• ArrayBuffer: message = binary, binaryType = “arraybuffer”
• binaryType is a property of web socket
var socket = new WebSocket(“ws://localhost:8080/BasicWebSocketExample/
echo");
socket.onmessage = function(event){
if(event.data instanceof Blob){
console.log("Blob message received", event.data);
var blob = new Blob(event.data);
}
}
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19. Javascript API - Other methods
• close()
• optional code & optional reason string
• send()
• accepts string, blob, ArrayBuffer, ArraryBufferView
connection.onopen = function() {
var intervalId = window.setInterval(function() {
if(connection.readyState != WebSocket.OPEN) {
window.clearInterval(intervalId);
return;
}
if(connection.bufferedAmount == 0)
connection.send(updatedModelData);
}, 50);
}
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20. Simple Example - Client side
• Used the wildfly archetype used in last TP
wildfly-javaee7-webapp-blank-archetype
• POM (added dependencies)
<dependency>
<groupId>org.jboss.spec.javax.websocket</groupId>
<artifactId>jboss-websocket-api_1.0_spec</artifactId>
<scope>provided</scope>
</dependency>
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21. Simple Example - Client side
<!DOCTYPE html>
<html><head>
<meta charset="UTF-8">
<title>Echo WebSocket</title>
<script type="text/javascript">
var socket = new WebSocket("ws://localhost:8080/BasicWebSocketExample/
echo");
//Event handler for the WebSocket connection opening
socket.onopen = function(event) {
console.log("Connection open...");};
//Event handler for closed connections
socket.onclose = function(event) {
console.log("Connection closed", event);};
//Event handler for errors in the WebSocket object
socket.onerror = function(event) {
console.log("WebSocket Error: " , event);};
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22. Simple Example - Client side
//Event handler for the WebSocket message reception
socket.onmessage = function(event){
alert(event.data)
if(typeof event.data === "string"){
console.log("String message received", event, event.data);
} else {
console.log("Other message received", event, event.data);
}
}
</script>
</head>
<body>
<button onclick='socket.send("hey dude")'>send</button>
</body>
</html>
Note: Server side in the coming slides ….
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23. JEE Client API - The Process
• The process for creating and deploying a WebSocket
endpoint follows.
• Create an endpoint class.
• Implement the lifecycle methods of the endpoint.
• Add your business logic to the endpoint.
• Deploy the endpoint inside a web application.
• Two ways to create endpoints
• Programmatic endpoints
• Annotated endpoints
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24. Programmatic Endpoints
• Endpoint is created by extending Endpoint class
• Three methods to override
• onOpen, onClose and onError
• onOpen is an abstract method (must implement)
• onOpen has session parameter which is
responsible for communication
• getBasicRemote give the remote end
• addMessageHandler method of the session parameter
is used to register message handlers
• message handler is implemented as anonymous class
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25. Programmatic Endpoints
package com.ece.jee;
public class EchoEndPoint extends Endpoint {
@Override
public void onOpen(final Session session, EndpointConfig config) {
session.addMessageHandler(new MessageHandler.Whole<String>() {
@Override
public void onMessage(String msg) {
try {
session.getBasicRemote().sendText(msg);
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
}
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26. Annotated Endpoints
• Deployment is easy through annotations
• Annotations mark the respective methods for each
event in the lifecycle
• onOpen
• onMessage
• onError
• onClose
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27. Endpoint Lifecycle Annotations
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Annotation Event Example
onOpen Connection
opened
@OnOpen
public void open(Session session,
EndpointConfig conf) { }
onMessage Message
received
@OnMessage
public void message(Session session,
String msg) { }
onError Connection
error
@OnError
public void error(Session session,
Throwable error) { }
onClose Connection
closed
@OnClose
public void close(Session session,
CloseReason reason) { }

28. Sending Messages
• Get session object from the annotated methods
• Get the remoteEndPoint object (either of two)
Session.getBasicRemote
Session.getAsyncRemote
• Send messages
void RemoteEndpoint.Basic.sendText(String text)
void RemoteEndpoint.Basic.sendBinary(ByteBuffer data)
void RemoteEndpoint.sendPing(ByteBuffer appData)
void RemoteEndpoint.sendPong(ByteBuffer appData)
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29. Simple Example - (cntd) Server Side
@ServerEndpoint("/echo")
public class Echo {
private Session session;
@OnOpen
public void connect(Session session) {
this.session = session;
System.out.println("session opened: " + session);
}
@OnClose
public void close() {
this.session = null;
System.out.println("session closed: " + session);
}
@OnMessage
public void onMessage(String msg) {
System.out.println("on message is called");
this.session.getAsyncRemote().sendText("Message from Server:" + msg);
}
}
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30. Sending message to all endpoints
@ServerEndpoint("/echoAll")
public class EchoAllEndPoint {
@OnMessage
public void onMessage(Session session, String msg) {
try {
for (Session sess : session.getOpenSessions()) {
if (sess.isOpen())
sess.getBasicRemote().sendText(msg);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
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31. Receiving messages
• onMessage annotations are used to handle incoming
messages
• At most three methods with this annotation are
allowed
• text
• binary
• pong
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32. Receiving messages
@ServerEndpoint("/receive")
public class ReceiveEndPoint {
@OnMessage
public void textMessage(Session session, String msg) {
System.out.println("Text message: " + msg);
}
@OnMessage
public void binaryMessage(Session session, ByteBuffer msg) {
System.out.println("Binary message: " + msg.toString());
}
@OnMessage
public void pongMessage(Session session, PongMessage msg) {
System.out.println("Pong message: "
+ msg.getApplicationData().toString());
}
}
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