Getting Started with WebSocket and Server-Sent Events in Java

Getting Started with
WebSocket and Server-Sent
Event in Java
Arun Gupta
blogs.oracle.com/arungupta, @arungupta

Copyright © 2013, Oracle and/or its affiliates. All rights reserved.3 Copyright © 2012, Oracle and/or its affiliates. All rights reserved. Insert Information Protection Policy Classification from Slide 16
Program
Agenda
§  WebSocket Primer
§  Getting Started with WebSocket
§  Server-Sent Event Primer
§  Getting Started with Server-Sent Event
§  Resources

Interactive Web Sites
§  HTTP is half-duplex
§  HTTP is verbose
§  Hacks for Server Push
–  Polling
–  Long Polling
–  Comet/Ajax
§  Complex, Inefficient, Wasteful

WebSocket to the Rescue
§  TCP based, bi-directional, full-duplex messaging
§  Originally proposed as part of HTML5
§  IETF-defined Protocol: RFC 6455
–  Handshake
–  Data Transfer
§  W3C defined JavaScript API
–  Candidate Recommendation

Establish a connection
Client
Handshake Request
Handshake Response
Server

Handshake Request
GET /chat HTTP/1.1 
Host: server.example.com 
Upgrade: websocket 
Connection: Upgrade 
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ== 
Origin: http://example.com 
Sec-WebSocket-Protocol: chat, superchat 
Sec-WebSocket-Version: 13 "

Handshake Response
HTTP/1.1 101 Switching Protocols 
Upgrade: websocket 
Connection: Upgrade 
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo= 
Sec-WebSocket-Protocol: chat "

ServerClient
Handshake Request
Handshake Response
Connected !
Establishing a Connection

Peer
(server)
Peer
(client)
Connected !
open open
close
message
error
message
message
message
message
Disconnected
WebSocket Lifecycle

WebSocket API
www.w3.org/TR/websockets/

Copyright © 2013, Oracle and/or its affiliates. All rights reserved.12 http://caniuse.com/websockets
Browser Support

Java API for WebSocket Features
§  API for WebSocket Server/Client Endpoints
–  Annotated (@ServerEndpoint, @ClientEndpoint)
–  Programmatic (Endpoint)
§  WebSocket opening handshake negotiation
§  Lifecycle callback handlers
§  Packaging with Java EE applications

Annotated Endpoint
import javax.websocket.*; 
 
@ServerEndpoint("/hello") 
public class HelloBean { 
 
@OnMessage 
public String sayHello(String name) { 
return “Hello “ + name; 
} 
}"

Annotations
Annotation Level Purpose
@ServerEndpoint" class Turns a POJO into a WebSocket Endpoint
@ClientEndpoint" class POJO wants to act as client
@OnMessage" method Intercepts WebSocket Message events
@PathParam"
method
parameter
Flags a matched path segment of a URI-template
@OnOpen" method Intercepts WebSocket Open events
@OnClose" method Intercepts WebSocket Close events
@OnError" method Intercepts errors during a conversation

@ServerEndpoint Attributes
value"
Relative URI or URI template
e.g. /hello or /chat/{subscriber-level}
decoders" list of message decoder classnames
encoders" list of message encoder classnames
subprotocols" list of the names of the supported subprotocols

Custom Payloads
@ServerEndpoint( 
value="/hello", 
encoders={MyMessage.class}, 
decoders={MyMessage.class} 
) 
public class MyEndpoint { 
. . . 
}"
"
"

Custom Payloads – Text
public class MyMessage implements Decoder.Text<MyMessage>, Encoder.Text<MyMessage> { 
private JsonObject jsonObject; 
 
public MyMessage decode(String s) { 
jsonObject = Json.createReader(new StringReader(s)).readObject(); 
return this;"
}"
public boolean willDecode(String string) { 
return true; // Only if can process the payload 
}"
"
public String encode(MyMessage myMessage) { 
return myMessage.jsonObject.toString(); 
} 
}"

Custom Payloads – Binary
public class MyMessage implements Decoder.Binary<MyMessage>, Encoder.Binary<MyMessage> { 
 
public MyMessage decode(byte[] bytes) { 
. . . 
return this;"
}"
public boolean willDecode(byte[] bytes) { 
. . . 
return true; // Only if can process the payload 
}"
"
public byte[] encode(MyMessage myMessage) { 
. . . 
} 
}"

Which methods can be @OnMessage ?
§  Exactly one of the following
–  Text: String, Java primitive or equivalent class, String and boolean,
Reader, any type for which there is a decoder
–  Binary: byte[], ByteBuffer, byte[] and boolean, ByteBuffer and
boolean, InptuStream, any type for which there is a decoder
–  Pong messages: PongMessage"
§  An optional Session parameter
§  0..n String parameters annotated with @PathParam"
§  Return type: String, byte[], ByteBuffer, Java primitive or class
equivalent or any type for which there is a encoder

Sample Messages
§  void m(String s);"
§  void m(Float f, @PathParam(“id”)int id);"
§  Product m(Reader reader, Session s);"
§  void m(byte[] b); or void m(ByteBuffer b);"
§  Book m(int i, Session s, @PathParam(“isbn”)String
isbn, @PathParam(“store”)String store);"

Chat Server
@ServerEndpoint("/chat")"
public class ChatBean {"
static Set<Session> peers = Collections.synchronizedSet(…); 
 
@OnOpen 
public void onOpen(Session peer) { 
peers.add(peer); 
} 
 
@OnClose 
public void onClose(Session peer) { 
peers.remove(peer); 
} 
 
. . ."

Chat Server
. . . 
 
@OnMessage"
public void message(String message, Session client) {"
for (Session peer : peers) { 
peer.getBasicRemote().sendObject(message); 
} 
} 
}"

https://blogs.oracle.com/arungupta/entry/collaborative_whiteboard_using_websocket_in

WebSocket Client
@ClientEndpoint 
public class HelloClient { 
@OnMessage 
public void message(String message, Session session) { 
// process message from server 
} 
} 
"
WebSocketContainer c = ContainerProvider.getWebSocketContainer(); 
c.connectToServer(HelloClient.class, “hello”);"
"

Programmatic Endpoint
public class MyEndpoint extends Endpoint { 
 
@Override 
public void onOpen(Session session) { 
session.addMessageHandler(new MessageHandler.Text() { 
public void onMessage(String name) { 
try { 
session.getBasicRemote().sendText(“Hello “ + name); 
} catch (IOException ex) { 
} 
}  
}); 
} 
}"

How to view WebSocket messages ?
Capture traffic on loopback

How to view WebSocket messages ?
chrome://net-internals -> Sockets -> View live sockets

Server-Sent Events
§  Part of HTML5 Specification
§  Server-push notifications
§  Cross-browser JavaScript API: EventSource"
§  Message callbacks
§  MIME type: text/eventstream"

EventSource API
dev.w3.org/html5/eventsource/

Server-Sent Events Example
var url = ‘webresources/items/events’; 
var source = new EventSource(url);"
source.onmessage = function (event) { 
console.log(event.data); 
} 
source.addEventListener(“size”, function(event) {"
console.log(event.name + ‘ ‘ + event.data); 
}"
Client-side

private final SseBroadcaster BROADCASTER = new SseBroadcaster(); 
 
@GET 
@Path("events”) 
@Produces(SseFeature.SERVER_SENT_EVENTS) 
public EventOutput fruitEvents() { 
final EventOutput eventOutput = new EventOutput(); 
BROADCASTER.add(eventOutput); 
return eventOutput; 
}

@POST 
@Consumes(MediaType.APPLICATION_FORM_URLENCODED) 
public void addFruit(@FormParam("fruit")String fruit) { 
FRUITS.add(fruit); 
 
// Broadcasting an un-named event with the name of the newly added item in data 
BROADCASTER.broadcast(new OutboundEvent.Builder().data(String.class, fruit).build()); 
 
// Broadcasting a named "add" event with the current size of the items collection in
data 
BROADCASTER.broadcast(new OutboundEvent.Builder().name("size").data(Integer.class,
FRUITS.size()).build()); 
}

WebSocket and Server-Sent Event
Competing technologies ?
WebSocket Server-Sent Event
Over a custom protocol Over simple HTTP
Full Duplex, Bi-directional Server-Push Only, Client->Server
is out-of-band (higher latency)
Native support in most browsers Can be poly-filled to backport
Not straight forward protocol Simpler protocol

WebSocket and Server-Sent Event
Competing technologies ?
WebSocket Server-Sent Event
Pre-defined message handlers Arbitrary events
Application-specific Built-in support for re-connection
and event id
Require server and/or proxy
configurations
No server or proxy changes
required
ArrayBuffer and Blob No support for binary types

Resources
§  Java API for WebSocket
–  Specification: jcp.org/en/jsr/detail?id=356
–  Reference Implementation: java.net/projects/tyrus
–  Integrated in GlassFish Server 4.0
–  Part of Java EE 7
§  Server-Sent Event
–  Integrated in Jersey and GlassFish Server 4.0
–  Not part of Java EE 7

The preceding material is intended to outline our general product
direction. It is intended for information purposes only, and may not be
incorporated into any contract. It is not a commitment to deliver any
material, code, or functionality, and should not be relied upon in making
purchasing decisions. The development, release, and timing of any
features or functionality described for Oracle’s products remains at the
sole discretion of Oracle.

Getting Started with WebSocket and Server-Sent Events in Java

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