getting started with websocket and server-sent events using java by arun gupta


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 "


Server Client

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 Endpoints/Client –  Annotation-driven (@ServerEndpoint) –  Interface-driven (Endpoint)

§  WebSocket opening handshake negotiation –  Client (@ClientEndpoint)

§  Integration with Java EE Web container


Hello World

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); } } }"


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”);"

"


Interface-driven 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 –  Part of Java EE 7 –  Integrated in GlassFish Server 4.0

§ Server-Sent Event –  Integrated in Jersey and GlassFish Server 4.0 –  Not part of Java EE 7

getting started with websocket and server-sent events using java by arun gupta

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