The document discusses WebSocket in Java, including: 1. WebSocket is a protocol providing full-duplex communications over a single TCP connection and was standardized by IETF as RFC 6455. 2. Sample WebSocket applications are demonstrated using the JavaWebSocket library, Java EE 7 with Tomcat, and Spring 4 with SockJS for fallback support to older browsers. 3. Code snippets show how to set up WebSocket servers and handlers in each approach to handle connections, messages, and disconnections from clients.

1. WebSockets in Java
From n00b to pro
22 Dec 2013, JavaDay, Pance Cavkovski

2. Theory
- WebSocket is a protocol providing full-duplex
communications over a single TCP
connection.
- Standardized by IETF as RFC 6455
- Designed to be implemented in web browsers
and web servers
- HTTP Upgrade request for initiating
connection
* Contents from Wikipedia: http://en.wikipedia.org/wiki/Web_sockets
GET /mychat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw==
Sec-WebSocket-Protocol: chat
Sec-WebSocket-Version: 13
Origin: http://example.com
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept:
HSmrc0sMlYUkAGmm5OPpG2HaGWk=
Sec-WebSocket-Protocol: chat
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3. Sample application
https://github.com/hsilomedus/web-sockets-samples
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4. public static void main(String[] args)
JavaWebSocket (web-socket-samples/javawebsockets)
public class Main extends WebSocketServer {
public Main() {
super(new InetSocketAddress(8887));
}
@Override
public void onOpen(WebSocket conn,
ClientHandshake handshake) {
//Handle new connection here
conn.send(“{”connected”: true}”);
}
@Override
public void onMessage(WebSocket conn,
String message) {
//Handle client received message here
}
* https://github.com/TooTallNate/Java-WebSocket
@Override
public void onClose(WebSocket conn, int code,
String reason, boolean remote) {
//Handle closing connection here
}
@Override
public void onError(WebSocket conn,
Exception exc) {
//Handle error during transport here
}
public static void main(String[] args) {
Main server = new Main();
server.start();
}
}
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5. Client
JavaScript WebSocket API
var socket = new WebSocket(“ws://localhost:8887”);
socket.onopen = function() {
//event handler when the connection has been established
socket.send(nickname);
};
socket.onmessage = function(message) {
//event handler when data has been received from the server
alert(message.data);
};
socket.onclose = function() {
//event handler when the socket has been properly closed
}
socket.onerror = function() {
//event handler when an error has occurred during communication
}
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6. Java EE 7: JSR 356 + Java7
Tomcat (>7.0.43) (web-socket-samples/eesockets)
@ServerEndpoint(“/chat”)
public class EESocketChatEndpoint {
@OnOpen
public void onOpen(Session session) {
//Handle new connection here
session.getBasicRemote()
.sendText(“{”connected”: true}”);
}
@OnMessage
public void onMessage(String message) {
//Handle client received message here
}
@OnClose
public void onClose(Session session,
CloseReason reason) {
//Handle closing connection here
}
@OnError
public void onError(Session session,
Throwable throwable) {
//Handle error during transport here
}
}
* JSR 356, Java API for WebSocket: http://www.oracle.com/technetwork/articles/java/jsr356-1937161.html (javax.websocket.*)
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7. Client
Pretty much the same JavaScript WebSocket API
var socket = new WebSocket(”ws://” + document.domain + “:8080/eesockets/chat”);
socket.onopen = function() {
//event handler when the connection has been established
socket.send(nickname);
};
socket.onmessage = function(message) {
//event handler when data has been received from the server
alert(message.data);
};
socket.onclose = function() {
//event handler when the socket has been properly closed
}
socket.onerror = function() {
//event handler when an error has occurred during communication
}
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8. Spring4
Static dispatcher servlet config
public class DispatcherServletInitializer extends
AbstractAnnotationConfigDispatcherServletInitializer{
@Override
protected Class<?>[] getRootConfigClasses() { return null; }
@Override
protected Class<?>[] getServletConfigClasses() {
return new Class<?>[] {WebConfig.class};
}
@Override
protected String[] getServletMappings() { return new String[]{“/”}; }
@Override
protected void customizeRegistration(Dynamic registration) {
registration.setInitParameter(“dispatchOptionsRequest”, “true”);
}
}
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9. Spring4
Static context config
@Configuration
@EnableWebMvc
@EnableWebSocket
@ComponentScan(basePackages={“mk.hsilomedus.springsockets.service”})
public class WebConfig extends WebMvcConfigurerAdapter implements WebSocketConfigurer {
public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
registry.addHandler(chatWenSocketHandler(), “/chat”).withSockJS();
}
@Bean
public WebSocketHandler chatWebSocketHandler() {
return new PerConnectionWebSocketHandler(ChatWebSocketHandler.class);
}
@Override
public void configureDefaultServletHandling(DefaultServerHandlerConfigurer configurer) {
configurer.enable();
}
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}

10. Spring4
WebSocketHandler (web-socket-samples/springsockets)
public class ChatWebSocketHandler extends
TextWebSocketHandler {
@Override
public void afterConnectionEstablished(
WebSocketSession session) {
//Handle new connection here
session.sendMessage(
“{”connected”: true}”);
}
@Override
public void handleTextMessage(
WebSocketSession session,
TextMessage message) {
//Handle message.getPayload() here
}
* http://blog.gopivotal.com/products/websocket-architecture-in-spring-4-0
@Override
public void afterConnectionClosed(
WebSocketSession session,
CloseStatus status) {
//Handle closing connection here
}
@Override
public void handleTransportError(
WebSocketSession session,
Throwable exception) {
//Handle error during transport here
}
}
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11. Client
SockJS
//I can now fallback to longpoll and do IE9!!!
var socket = new SockJS(”http://” + document.domain + “:8080/springsockets/chat”);
socket.onopen = function() {
//event handler when the connection has been established
socket.send(nickname);
};
socket.onmessage = function(message) {
//event handler when data has been received from the server
alert(message.data);
};
socket.onclose = function() {
//event handler when the socket has been properly closed
}
socket.onerror = function() {
//event handler when an error has occurred during communication
}
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12. socket.close();
Thanks for your attention
- The whole source code is available on github:
https://github.com/hsilomedus/web-sockets-samples
- /javawebsockets – with the JavaWebSocket library
- /eesockets – with Tomcat 7.0.47
- /springsockets – with Spring4 RC2 and Tomcat 7.0.47
- All three are eclipse projects running on Java7
- Questions?
- https://twitter.com/hsilomedus, http://hsilomedus.me/
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