Support slides for the JUG Louvain-La-Neuve

1. Java User Group Louvain-La-Neuve
9/10/2014 – EPHEC LLN
Rudy Vissers
Coding Java WebSocket Applications
Using the JSR 356 API

2. Introduction
● HTTP(Hypertext Transfer Protocol) is a
stateless request-response protocol.
● This simple design of the HTTP protocol
makes it very scalable but inefficient and
unsuitable for highly interactive real-time web
applications : Chat applications, Multiplayer
games, etc.
● HTTP was designed for document sharing
and not for building today’s highly
interactive web applications.
● HTTP is bit chatty in nature,

3. Introduction cont.
● Before the HTTP 1.1 version, every request
made to the server resulted in a new
connection.
● This was improved in HTTP 1.1 with the
introduction of HTTP persistence connections.
● Persistent connections allowed web browsers
to reuse the same connection for fetching
images, scripts, etc.

4. Introduction cont.
● HTTP was designed to be half-duplex which
means it allows transmission of data in just one
direction at a time.
● A Walkie-talkie is an example of a half
duplex device because only one person can
speak at a time.
● Developers have created some workarounds or
hacks to overcome this HTTP shortcoming :
polling, long polling, and streaming.

5. Introduction cont.
● With polling, the client makes synchronous
calls to get information from the server. Do you
have something for me ?
● If the server has new information available it will
send back data in the response.
● Otherwise, no information will be sent to the
client and the client will again make a new
connection after sometime.
● This is very inefficient but a very simple way
to achieve real-time behavior.

6. What is a WebSocket?
● A WebSocket is asynchronous, bidirectional,
full-duplex messaging implementation over a
single TCP connection.
● WebSockets are not a HTTP connection , but
use HTTP to bootstrap a WebSocket
connection.
● A full-duplex system allows communication in
both directions simultaneously.
● Telephones lines are an example of a full-duplex
device, since they allow both callers to
speak and be heard at the same time.

7. What is a WebSocket? cont.
● RFC 6455 :
The WebSocket Protocol :
http://tools.ietf.org/html/rfc6455
● JSR 356 :
Java API for WebSocket :
https://jcp.org/en/jsr/detail?id=356
● WebSocket JavaScript API :
http://www.w3.org/TR/2011/WD-websockets-
20110419

8. Browsers : can I use ?
● WebSockets are supported by all the latest
browsers.

9. How Does a WebSocket Work?
● Every WebSocket connection begins its life as
an HTTP request.
● The HTTP request is much like another
request, except that it has an Upgrade header.
● The Upgrade header indicates that a client
would like to upgrade the connection to
different protocol(s).
● For WebSockets it will upgrade to the
WebSocket protocol.
● The WebSocket connection is established by
upgrading from HTTP protocol to the

10. WebSocket is more complex than
HTTP
● You can establish an HTTP connection with a
telnet client, telnet localhost 80 :-)
but you probably cannot do the same with WS.
● Even if you ignored the handshake
requirements (which include the use of the
SHA1 hash function), you would then be unable
to properly mask and frame the data to be sent
and the server would close the connection.

11. WebSocket is more complex than
HTTP cont.
● WebSocket connections are intended to be
more persistent than HTTP connections.
● If you only want to receive an update every 30
minutes, you will want to go with HTTP.
● If you want to receive updates every second, a
WebSocket might be a better option, because
establishing an HTTP connection takes a lot
of time.

12. WebSockets simplify real-time
application architectures
● For these kind of applications WebSockets are
more efficient and performant than other
workarounds like polling.
● They require less bandwidth and reduce
latency.
● WebSockets do not require headers to send
messages between peers.
● This considerably lowers the required
bandwidth.

13. WebSocket Use Cases
● Chat applications
● Multiplayer games
● Stock trading or financial applications
● Collaborative document editing
● Social networking applications

14. Java APIs
● JSR 356, Java API for WebSocket, specifies
Java API that developers can use to integrate
WebSockets into their applications both on the
server side as well as on the Java client side.
● JSR 356 is part of the upcoming Java EE 7
standard.
● This means all Java EE 7 compliant application
servers will have an implementation of the
WebSocket protocol that adheres to the JSR
356 standard.
● Developers can also use JSR 356 outside Java

15. Java APIs cont.
● A Java client can use JSR 356 compliant client
implementation to connect to a WebSocket
server (Tyrus).
● For web clients, developers can use
WebSocket JavaScript API to communicate
with WebSocket server.
● The difference between a WebSocket client
and a WebSocket server lies only in the means
by which the two are connected.
● A WebSocket client is a WebSocket endpoint
that initiates a connection to a peer.

16. ● Time to code !