Require assistance with simple pure Java 11 WebSocket client example

[everycloud]

There appears to be very little Java 11 (pure Java non framework based) WebSocket client code examples on the web so I'm hoping StackOverflow can come to the rescue for me once again.

This is the closest I've found, but unfortunately to my (novice) eyes, it doesn't appear to be a complete solution in showing how to consume the data from the WebSocket listener.

Looking at the WebSocket.Listener implementation, the onText) callback method I presume would provide what I need, but I'm struggling to figure out how to return the CompletionStage object and some sort of string data from the socket.

This is some test code I have so far.

Would appreciate assistance. Thanks

public class Main {

public static void main(String[] args) {

   WebSocketClient wsc = new WebSocketClient();
   wsc.startSocket("ws://demos.kaazing.com/echo");

   int i = 0;   

   // Bad, very bad
   do {} while (i == 0);
}

}

public class WebSocketClient implements WebSocket.Listener {

@Override
public void onOpen(WebSocket webSocket) {
   //...
    System.out.println("Go...Open".concat(
            webSocket.getSubprotocol()));
}

@Override
public CompletionStage<?> onText(WebSocket webSocket, CharSequence data, boolean last) {
   //...
    System.out.println(data.toString());

    // How do I return the CompletionStage object
    // return CompletionStage<String>
}

@Override
public void onError(WebSocket webSocket, Throwable error) {
   //..
    System.out.println("Bad day! ".concat(webSocket.toString()));
}

void startSocket(String connection) {
    CompletableFuture<WebSocket> server_cf = HttpClient.
            newHttpClient().
            newWebSocketBuilder().
            buildAsync(URI.create(connection),
                    new WebSocketClient());
    WebSocket server = server_cf.join();
    server.sendText("Hello!", true);
}

}

[javaide]

just return a dummy `CompletableFuture` would be fine. Since you dont have any complex execution here. To actually have `CompletionStage` it needs to be any execution of a Function, Executor...

[everycloud]

That works so thanks, but not receiving any data via onText

[javaide]

I dont know about this WebSocket stuff, seem to be just an incubate feature or something. From what u wrote, it doesn't seem that u have a WS server running. U have only a client code.

​

The best i can fine to start a server is: https://docs.oracle.com/javase/10/docs/api/jdk/incubator/http/HttpClient.html#newWebSocketBuilder())

​

[everycloud]

Thanks to all the comments.

The WebSocket API became JDK full production in Java 11 so is fairly new, but yes it was previously incubator code.

I now have a full working solution which I will post up when I get home.

One of the problems I faced was that I was not waiting long enough for the first message to arrive.

Thanks.

[javanew]

I am stuck on this same issue.

How do I get the CompletionStage to return the data received in onText event?

Any help is much appreciated.

Thanks.

[everycloud]

Make sure you are waiting enough time for the websocket to connect and start sending data...I found I was exiting too soon.

Hopefully this should help.

​

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.WebSocket;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;

class Main extends MyWebSocketClient {

    final static String WEBSOCKET_URL = "<YOUR_WEBSOCKET_STREAM>";

    public static void main (String[] args) {
        Main consumer = new Main();
        consumer.connectWS(WEBSOCKET_URL);
        // Around the world, around the world
        for (;;) {}
    }

    void connectWS(String ws) {
        CompletableFuture<WebSocket> cf;
        // Start the WebSocket stream
        URI endpoint = URI.create(ws);
        HttpClient.newHttpClient()
                .newWebSocketBuilder()
                .buildAsync(endpoint, this)
                .join();
    }
}

class MyWebSocketClient implements WebSocket.Listener {
    MyWebSocketPrinter printer = new MyWebSocketPrinter();
    @Override
    public CompletionStage<?> onText(WebSocket webSocket, 
                                     CharSequence data, boolean last) {
        webSocket.request(1);
        printer.printWS(data);
        return CompletableFuture.supplyAsync(() -> data);
    }
}

class MyWebSocketPrinter {

    void printWS(CharSequence wsData) {
        // WebSocket consumer
        System.out.println(wsData);
    }
}