This post briefly demonstrates how to develop and deploy (server and client) websocket endpoints using the programmatic version of the Java Websocket API.

Step #1 - Extend the javax.websocket.Endpoint Class

public class ProgrammaticEchoEnpoint extends Endpoint {

    @Override
    public void onOpen(Session session, EndpointConfig config) {
        System.out.println("Peer " + session.getId() + " connected");
        session.addMessageHandler(new MessageHandler.Whole<String>() {
            @Override
            public void onMessage(String message) {
                try {
                    session.getBasicRemote().sendText("Got message from " + session.getId() + "\n" + message);
                } catch (IOException ex) {
                }
            }
        });
    }

    @Override
    public void onClose(Session session, CloseReason closeReason) {
        System.out.println("Peer " + session.getId() + " disconnected due to " + closeReason.getReasonPhrase());
    }

    @Override
    public void onError(Session session, Throwable error) {
        System.out.println("Error communicating with peer " + session.getId() + ". Detail: "+ error.getMessage());
    }
}

Let’s code the client endpoint as well (using the same set of APIs):

public class ProgrammaticEchoClient extends Endpoint {

    @Override
    public void onOpen(Session session, EndpointConfig config) {
        System.out.println("Connected to server");
    }

    //a message handler and other life cycle implementations have been skipped on purpose...

}

Step #2 - Implement the ServerApplicationConfig Interface

It is part of the javax.websocket.server package and can be overridden to implement custom logic for endpoint deployment (for both annotated as well as programmatic endpoints)

public class CustomServerAppConfigProvider implements ServerApplicationConfig {

    @Override
    public Set<ServerEndpointConfig> getEndpointConfigs(Set<Class<? extends Endpoint>> endpointClasses) {
        Set<ServerEndpointConfig> result = new HashSet<>();
        for (Class epClass : endpointClasses) {
            //need to ignore Client endpoint class
            if (epClass.equals(ProgrammaticChatEndpoint.class)) {
                ServerEndpointConfig sec = ServerEndpointConfig.Builder.create(epClass, "/letschat").build();
                result.add(sec);
            }
        }
        return result;
    }

    @Override
    public Set<Class<?>> getAnnotatedEndpointClasses(Set<Class<?>> scanned) {
        return Collections.emptySet();
    }
}

What About the Client Endpoint?

If required, you can create a your own instance of ClientEndpointConfig and use it while initiating a connection to the websocket server endpoint:

WebSocketContainer webSocketContainer = ContainerProvider.getWebSocketContainer();
ClientEndpointConfig config = ClientEndpointConfig.Builder.create().decoders(StockTickDecoder.class).build();
Session session = webSocketContainer.connectToServer(StockTickerClient().class, config, 
                                                    new URI("ws://hotstocks.com/ticker"));

Notes

• Both the client as well as server endpoint config objects are nothing but object (programmatic) equivalents of the elements (value, encoders, decoders, configurator etc.) of the @ServerEndpoint and @ClientEndpoint annotations
• Separate builder classes (ServerEndpointConfig.Builder and ClientEndpointConfig.Builder) were used to create server and client configuration instances respectively
• The creation of a ServerEndpointConfig instance is mandatory since server endpoints cannot be deployed without a URI. This is not the case with client endpoints though – all they do is connect to an existing server endpoint.
• The endpoint config (server & client) have the notion of a configurator which can be created and set via the respective builder methods.

Stay tuned for some more Websocket related action in the near future.