Sequential composition for arbitrary number of calls in Vertx with Futures

Question

We use Futures in vertx in examples like:

Future fetchVehicle = getUserBookedVehicle(routingContext, client);

        fetchVehicle.compose         


        

Answer 1

If you want to feed the response from the previous request to the next request, and suppose you have different handlers for each response. You can add a helper method

private  Future chain(Future init, List>> handlers) {
    Future result = init;
    for (Function> handler : handlers) {
        result = result.compose(handler);
    }
    return result;
}

And then change your code like this

    Future fetchVehicle = getUserBookedVehicle(routingContext, client);

    Function> vehicleResponseHandler = vehicleJson ->
        vehicleDoor(routingContext, client, vehicleJson, lock);

    Function> anotherTrivialHandler = someJsonObj -> {
        // add here new request by using information from someJsonObj
        LOG.info("Hello from trivial handler {} ", someJsonObj);
        return Future.succeededFuture(someJsonObj);
    };

    List>> handlers = new ArrayList<>();

    handlers.add(vehicleResponseHandler);
    handlers.add(anotherTrivialHandler);

    chain(fetchVehicle, handlers).setHandler( asyncResult -> {
        if (asyncResult.succeeded()) {
            handler.handle(Future.succeededFuture(new AsyncReply(200, "OK")));
        } else {
            handler.handle(Future.failedFuture(asyncResult.cause()));
        }
    });

But there is a limitation for this implementation which requires each chained Future must have the same type parameter T.