spring - springx2013-websocket

WebSocket Apps
Spring Framework 4 (part 1)

Rossen Stoyanchev

Part 1:

Comprehensive Intro to WebSocket

in Spring Framework 4.0

Part 2:

Building WebSocket Applications

This Presentation

https://github.com/rstoyanchev/

springx2013-websocket

The WebSocket Protocol

How Did We Get Here?

How WebSocket Works

Practical Considerations

Java WebSocket API

Relation To the Servlet API

Server Availability

Spring Framework 4.0

Example

import org.springframework.web.socket.*;


public class MyHandler extends TextWebSocketHandlerAdapter {


  @Override
  public void handleTextMessage(WebSocketSession session,
      TextMessage message) throws Exception {

    session.sendMessage(message);

  }

}

Basic Config

@Configuration
@EnableWebSocket
public class WsConfig implements WebSocketConfigurer {


  @Override
  public void registerWebSocketHandlers(
        WebSocketHandlerRegistry registry) {

    registry.addHandler(new MyHandler(), "/echo");
  }

}

Browser client

var ws = new WebSocket("wss://localhost:8080/myapp/echo");

ws.onopen = function () {
  console.log("opened");
};

ws.onmessage = function (event) {
  console.log('message: ' + event.data);
};

ws.onclose = function (event) {
  console.log('closed:' + event.code);
};

HandshakeInterceptor

Add Interceptor

@Configuration
@EnableWebSocket
public class WsConfig implements WebSocketConfigurer {


  @Override
  public void registerWebSocketHandlers(
        WebSocketHandlerRegistry registry) {

    registry.addHandler(echoHandler(), "/echo")
        .addInterceptors(new MyHandshakeInterceptor());
  }

}

Per-Session Handler

Configure Per-Session Handler

@Configuration
@EnableWebSocket
public class WsConfig implements WebSocketConfigurer {


  @Bean
  public WebSocketHandler snakeHandler() {
    return new PerConnectionWebSocketHandler(
        SnakeWebSocketHandler.class);
  }


  @Override
  public void registerWebSocketHandlers(
        WebSocketHandlerRegistry registry) {

    registry.addHandler(snakeHandler(), "/snake");
  }

}

Deployment Notes

SockJS

SockJS Protocol

SockJS URL Scheme

    GET  /echo

    GET  /echo/info

    POST /echo/<server>/<session>/<transport>

SockJsService

Configure SockJS

@Configuration
@EnableWebSocket
public class WsConfig implements WebSocketConfigurer {


  @Override
  public void registerWebSocketHandlers(
        WebSocketHandlerRegistry registry) {

    registry.addHandler(myHandler(), "/echo").withSockJS();
  }

}

WebSocket Handler

(same as before)

import org.springframework.web.socket.*;


public class MyHandler extends TextWebSocketHandlerAdapter {

  @Override
  public void handleTextMessage(WebSocketSession session,
      TextMessage message) throws Exception {

    session.sendMessage(message);

  }

}

Server Versions

Detecting Client Disconnects

WebSocket/SockJS Sample

https://github.com/rstoyanchev/

spring-websocket-test

Questions?

WebSocket Apps
Spring Framework 4 (part 2)

Rossen Stoyanchev

Non-Trivial Applications

Using a WebSocket API is a bit like

writing a custom Servlet application

Except WebSocket is even lower level

You'll likely have 1 WebSocket handler

for the whole application

Annotations can't help much either...

...not without making assumptions about

what's in a message!

"The basic issue is there isn't enough information in an incoming websocket message for the container to know where to route it if there are multiple methods where it may land."

Danny Coward, JSR-356 lead
In response to question on user mailing list

"The subprotocol attribute of the handshake might serve as a useful place to attach this kind of message description/meta data, or some JSR356 specific headers in the handshake. Of course, the other issue is that the other end is often javascript, which would need to participate in some way in such a scheme."

"These are all things we'll likely look at in the next version."

From next reply on same thread

The Sub-protocol Attribute

Furthermore..

Message Brokers an Option?

We Need a Bit of Both Worlds

Many Approaches Exist

The Spring Approach

STOMP

STOMP Frame

Client-to-Server Commands

Server-to-Client Commands

"Destination" Header

Keep in mind:

A server cannot send unsolicited messages

client must subscribe first

Example

Client Sends Message

Example

Client Subscribes To Receive Messages

Example

Client Receives Message

STOMP vs plain WebSocket

STOMP over WebSocket

Spring Framework 4.0

Basic Configuration

@Configuration
@EnableWebSocketMessageBroker
public class Config
    implements WebSocketMessageBrokerConfigurer{


  @Override
  public void registerStompEndpoints(StompEndpointRegistry r){
    r.addEndpoint("/stomp");
  }

  @Override
  public void configureMessageBroker(MessageBrokerConfigurer c){
    c.enableSimpleBroker("/topic/");
    c.setApplicationDestinationPrefixes("/app");
  }

}

• 
  
  

Handle a Message

@Controller
public class GreetingController {


  @MessageMapping("/greetings")
  public void handle(String greeting) {
    // ...
  }

}

@MessageMapping

Return Values

Send via Return Value

@Controller
public class GreetingController {

  // A message is broadcast to "/topic/greetings"

  @MessageMapping("/greetings")
  public String greet(String greeting) {
      return "[" + getTimestamp() + "]: " + greeting;
  }

}

Send to Different Destination

with @SendTo

@Controller
public class GreetingController {


  @MessageMapping("/greetings")
  @SendTo("/topic/wishes")
  public String greet(String greeting) {
      return "[" + getTimestamp() + "]: " + greeting;
  }

}

Send via SimpMessagingTemplate

@Controller
public class GreetingController {

  @Autowired
  private SimpMessagingTemplate template;


  @RequestMapping(value="/greetings", method=POST)
  public void greet(String greeting) {
    String text = "[" + getTimeStamp() + "]:" + greeting;
    this.template.convertAndSend("/topic/wishes", text);
  }

}

Handle Subscription

(Request-Reply Pattern)

@Controller
public class PortfolioController {


  @SubscribeEvent("/positions")
  public List<Position> getPositions(Principal p) {
    Portfolio portfolio = ...
    return portfolio.getPositions();
  }

}

Plug in Message Broker

Steps to Use Message Broker

Enable "Broker Relay"

@Configuration
@EnableWebSocketMessageBroker
public class Config
    implements WebSocketMessageBrokerConfigurer{


  @Override
  public void configureMessageBroker(MessageBrokerConfigurer c){
    c.enableStompBrokerRelay("/queue/", "/topic/");
    c.setApplicationDestinationPrefixes("/app");
  }

}

Authentication

Destination "/user/**"

UserDestinationHandler

Client Subscribes

To "/user/queue/..."

var socket = new SockJS('/myapp/portfolio');
var client = Stomp.over(socket);

client.connect('', '', function(frame) {

  client.subscribe("/user/queue/trade-confirm",function(msg){
    // ...
  });

  client.subscribe("/user/queue/errors",function(msg){
    // ...
  });

}

Send Reply To User

@Controller
public class GreetingController {

  // Message sent to "/user/{username}/queue/greetings"

  @MessageMapping("/greetings")
  @SendToUser
  public String greet(String greeting) {
      return "[" + getTimestamp() + "]: " + greeting;
  }

}

Send Error To User

@Controller
public class GreetingController {



  @MessageExceptionHandler
  @SendToUser("/queue/errors")
  public String handleException(IllegalStateException ex) {
    return ex.getMessage();
  }

}

Send Message To User

via SimpMessagingTemplate

@Service
public class TradeService {

  @Autowired
  private SimpMessagingTemplate template;


  public void executeTrade(Trade trade) {
    String user = trade.getUser();
    String dest = "/queue/trade-confirm";
    TradeResult result = ...
    this.template.convertAndSendToUser(user, dest, result);
  }

}

Managing Inactive Queues

(with Full-Featured Broker)

Stock Portfolio App

https://github.com/rstoyanchev/

spring-websocket-portfolio