WebSocket & JSON
Java APIs Hackday
By Somay Nakhal @SomayNakhal
David Illsley @davidillsley
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Hackday ?
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Adapt A JSR programme
Explore new APIs
JSR 353 JSON Processing API
JSR 356 WebSockets API
Provide feedback
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WebSocket and Java
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Interactive web application
HTTP is half-duplex
Polling
Long Polling
Comet/Ajax
Complex, Inefficient, Wasteful
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Enter WebSocket Protocol
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TCP based, bi-directional, full-duplex messaging
Part of HTML5
IETF-defined Protocol: RFC 6455
W3C defined JavaScript API
Uses HTTP upgrade handshake
Supports HTTP proxies, filtering, authentication and intermediaries
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How does it work?
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Establish connection (Single TCP connection)
Send messages in both direction (Bi-directional)
Send messages independent of each other (Full Duplex)
End connection
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Browser Support
caniuse.com
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WebSocket API (JavaScript)
var websocket = new WebSocket("ws://www.host.com/path");
websocket.onopen = function(evt) { onOpen(evt) };
websocket.onclose = function(evt) { onClose(evt) };
websocket.onmessage = function(evt) { onMessage(evt) };
websocket.onerror = function(evt) { onError(evt) }; }
function onMessage(evt) { alert( evt.data); }
function onError(evt) { alert( evt.data); }
websocket.send("client to server");
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JSR 356
Java API for WebSocket
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JSR 356 Java API for WebSocket
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Client and Server WebSocket protocol APIs in Java
Integration with Java EE Web container
Reference Implementation:
– http://java.net/projects/tyrus
– Bundled in latest Glassfish 4 builds
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Terminology
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Endpoint: Client or server
Connection: Network connection between two endpoints
Peer: Other endpoint of the connection
Session: represents a sequence of websocket interactions between
and end point and a peer
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Annotations
 @WebSocketEndpoint
– Class level annotation for websocket server endpoint
 @WebSocketClient
– Class level annotation for websocket client endpoint
 @WebSocketOpen
– Method level annotation signifies a method to be called whenever a new
client connects to this endpoint
 @WebSocketClose
– Method level annotation signifies a method to be called whenever a new
client is about to disconnects from this endpoint
 @WebSocketMessage
– Method level annotation signifies a method to be called whenever an
incoming message is received
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Some Code!
@WebSocketEndpoint("/hello-world")
public class HelloWorld {
@WebSocketMessage
public String sayHello(String name) {
return "Hello " + name;
}
}
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More Code!
@WebSocketEndpoint("/hello-world")
public class HelloWorld {
private Set<Session> peers = Collections.synchronizedSet(…)
@WebSocketOpen
public void onOpen (Session peer) {
peers.add(peer);
}
private void sendMessageToPeer(String message, Session peer) {
peer.getRemote().sendString(s);
}
}
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JSON and Java
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In the beginning...
There was XML
... and the DOM... and SAX...
Then, after much gnashing of teeth, there was JSON
{ "message" : "Hello World!" }
More at json.org and wikipedia
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tumbleweed...
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Not Quite
From: http://www.json.org/license.html
"The Software shall be used for Good, not Evil."
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And many more...
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org.json.me.
Jackson JSON Processor.
Json-lib.
JSON Tools.
Stringtree.
SOJO.
Jettison.
json-taglib.
XStream.
Flexjson.
JON tools.
Argo.
jsonij.
fastjson.
mjson.
jjson.
json-simple.
json-io.
JsonMarshaller.
google-gson.
Json-smart.
FOSS Nova JSON.
(list from json.org)
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Fast-forward to December 2011
JSR 353: JavaTM API for JSON Processing
"JSON(JavaScript Object Notation) is a lightweight data-interchange format.
Many popular web services use JSON format for invoking and returning the
data. Currently Java applications use different implementation libraries to
produce/consume JSON from the web services. Hence, there is a need to
standardize a Java API for JSON so that applications that use JSON need
not bundle the implementation libraries but use the API. Applications will be
smaller in size and portable."
http://jcp.org/en/jsr/detail?id=353
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Goals/Non Goals
"The goal of this specification is to develop such APIs to:
* Produce and consume JSON text in a streaming fashion(similar to StAX API
for XML)
* Build a Java object model for JSON text using API classes(similar to DOM
API for XML)
Non-goals of this specification include:
* Binding of JSON text to Java objects and vice versa."
"This JSR is targeted for Java SE 6 or higher and Java EE 7 or higher
platforms."
http://jcp.org/en/jsr/detail?id=353
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Fast-forward to February 2013
Pretty much done
Just finished the formal public review phase
Looking for final feedback from JUGs
... and to get the word out about what's coming
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Some code...
JsonGenerator generator = Json.createGenerator(System.out)
// or generator = Json.createGenerator(servletResponse.getWriter())
generator
.writeStartObject()
.write("firstName", "John")
.write("lastName", "Smith")
.write("age", 25)
.writeStartObject("address")
.write("streetAddress", "21 2nd Street")
.write("city", "New York")
.write("state", "NY")
.write("postalCode", "10021")
.writeEnd()
.writeStartArray("phoneNumber")
.writeStartObject()
.write("type", "home")
.write("number", "212 555-1234")
.writeEnd()
.writeStartObject()
.write("type", "fax")
.write("number", "646 555-4567")
.writeEnd()
.writeEnd()
.writeEnd();
generator.close();
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Produces
{
"firstName": "John", "lastName": "Smith", "age": 25,
"address" : {
"streetAddress": "21 2nd Street",
"city": "New York",
"state": "NY",
"postalCode": "10021"
},
"phoneNumber": [
{"type": "home", "number": "212 555-1234"},
{"type": "fax", "number": "646 555-4567"}
]
}
(JavaDoc - JsonGenerator) http://bit.ly/11CwMde
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Or to build an object model...
JsonObject value = Json.createObjectBuilder()
.add("firstName", "John")
.add("lastName", "Smith")
.add("age", 25)
.add("address", Json.createObjectBuilder()
.add("streetAddress", "21 2nd Street")
.add("city", "New York")
.add("state", "NY")
.add("postalCode", "10021"))
.add("phoneNumber", Json.createArrayBuilder()
.add(Json.createObjectBuilder()
.add("type", "home")
.add("number", "212 555-1234"))
.add(Json.createObjectBuilder()
.add("type", "fax")
.add("number", "646 555-4567")))
.build();
// or from a stream..
JsonObject value2 = Json.createReader(inputStream).readObject();
(JavaDoc - JsonObject) bit.ly/11CwMde
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And to read things from it...
int age = value2.getIntValue("age", 18);
JsonObject address = value2.getValue("address", JsonObject.class);
String city = "London";
if(address != null){
city = address.getStringValue("city", "London");
}
JsonArray phoneNumbers = value2.getValue("phoneNumber", JsonArray.class);
if(phoneNumbers != null){
for(JsonValue val: value2){
if(val instanceof JsonObject){
JsonObject jo = (JsonObject)val;
System.out.println(jo.getStringValue("number","Number Missing");
}
}
}
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And a low-level event API
Event event = parser.next(); // START_OBJECT
event = parser.next();
// KEY_NAME
event = parser.next();
// VALUE_STRING
parser.getString();
// "John"
(JavaDoc - JsonParser) bit.ly/VzGWEr
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JSON Hacks/Workshop
Latest version of the library not in Glassfish yet, so a small standalone
maven project
https://github.com/davidillsley/json-workshop
Includes tests for some uncompleted code operating on stored JSON..
see the README for more.
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