🌐 Websockets

In this section, we illustrate how to create and manage Websockets in Flash, which are used to establish a bidirectional communication channel between the client and the server.

Understanding Websockets

Websockets are a communication protocol that provides full-duplex communication channels over a single TCP connection. Unlike HTTP, which is a request-response protocol, Websockets allow for real-time, low-latency communication between the client and the server.

Imagine a scenario where you need to send real-time updates to the client, such as a chat application or a live feed: if you were to use HTTP, you would need to poll the server at regular intervals to check for updates, which is inefficient and resource-intensive.

Creating a Websocket

To create a Websocket in Flash, you need to extend the WebsocketHandler class and override the onOpen, onMessage, onClose, and onError methods. These methods are called when the Websocket connection is opened, a message is received, the connection is closed, and an error occurs, respectively, and they provide you with an instance of the WebSocketSession object to be able to interact with it.

public class MyWebsocketHandler extends WebsocketHandler {
    @Override
    public void onOpen(WebSocketSession session) {
        System.out.println("WebSocket connection opened");
    }

    @Override
    public void onClose(WebSocketSession session, int statusCode, String reason) {
        System.out.println("WebSocket connection closed");
    }

    @Override
    public void onMessage(WebSocketSession session, String message) {
        System.out.println("Received message: " + message);

        //optionally send a reponse back to the client
        session.sendMessage("I received your message!");
    }

    @Override
    public void onError(WebSocketSession session, Throwable error) {
        System.out.println("WebSocket error: " + error.getMessage());
    }
}

To register your Websocket handler with the server, you can use the server.ws() method:

public class Example {
    public static void main(String[] args) {
        FlashServer server = new FlashServer(8080);

        server.ws("/ws")
            .register(new MyWebsocketHandler());

        server.start();
    }
}

Interacting with Websockets sessions

The WebSocketSession object provides methods to interact with the Websocket session, such as sending messages, closing the connection, and getting the remote address and session ID.

Method	Params	Description
getChannel()	none	Returns an instance of AsynchronousSocketChannel useful for retrieving info about the client .
getRequestInfo()	none	Returns an instance of RequestInfo containing all sorts of information about the request (headers, method, path etc.) .
getPath()	none	Returns the path to the websocket endpoint as a String.
getId()	none	Returns the id of the websocket session as a String, useful if you want to keep track of the connected clients in a custom manager.
getBuffer()	none	Returns the ByteBuffer for that session.
sendMessage()	String message	Sends the message to the client as a String. it's up to the developer to stringify and de-stringify any data you want to send back and forth
close()	none	Closes the websocket session.

NOTE

WebsocketHandler includes a setId(String id) method for overriding the default session ID. Unless you have a specific reason to change it, it's best to leave it as is.

Similarly, the setBuffer(ByteBuffer buffer) method allows you to override the default buffer. If you're unsure about this, it's recommended to keep the default setting.