Method watchMultiple

java/lib/src/main/java/io/github/ccxt/Exchange.java:1712–1756

(Object url, Object messageHashes2, Object message, Object subscribeHashes2, Object subscription)

    // Note: a single subscribe message is sent for all symbols, matching JS/C# design.
    // Exchange-specific code is responsible for building the message with all symbols.
    @SuppressWarnings("unchecked")
    public CompletableFuture<Object> watchMultiple(Object url, Object messageHashes2, Object message, Object subscribeHashes2, Object subscription) {
        var client = this.client(url);

        List<Object> messageHashes = (List<Object>) messageHashes2;
        io.github.ccxt.ws.Future[] futures = new io.github.ccxt.ws.Future[messageHashes.size()];
        for (int i = 0; i < messageHashes.size(); i++) {
            futures[i] = client.future(messageHashes.get(i).toString());
        }
        var raceFuture = io.github.ccxt.ws.Future.race(futures);

        List<String> missingSubscriptions = new java.util.ArrayList<>();
        if (subscribeHashes2 instanceof List<?> subscribeHashes) {
            for (Object sh : subscribeHashes) {
                if (sh == null) continue;
                String subHash = sh.toString();
                if (client.subscriptionsMap().putIfAbsent(subHash, subscription != null ? subscription : true) == null) {
                    missingSubscriptions.add(subHash);
                }
            }
        }

        if (subscribeHashes2 == null || !missingSubscriptions.isEmpty()) {
            client.connect(0).thenAccept(connected -> {
                if (message != null) {
                    try {
                        client.send(message);
                    } catch (Exception ex) {
                        for (String subHash : missingSubscriptions) {
                            client.subscriptionsMap().remove(subHash);
                        }
                        raceFuture.reject(ex);
                    }
                }
            }).exceptionally(ex -> {
                for (String subHash : missingSubscriptions) {
                    client.subscriptionsMap().remove(subHash);
                }
                raceFuture.reject(ex);
                return null;
            });
        }

        return raceFuture.getFuture();
    }

    public void handleMessage(Client client, Object message) {
        // Base implementation — overridden by pro exchange classes