Danger of instantiating a class in a verticle vert.x

Question

I explain my problem, I have a verticle in which I defined all the routes. And I have simple java classes that contain methods that I call in my verticle depending on the route. For example, my downloadFile() method is in the MyFile class like this:

    public class MyFile {

        public final void downloadFile(RoutingContext rc, Vertx vertx) {
            final HttpServerResponse response = rc.response();
            response.putHeader("Content-Type", "text/html");
            response.setChunked(true);

            rc.fileUploads().forEach(file -> {

                final String fileNameWithoutExtension = file.uploadedFileName();

                final JsonObject jsonObjectWithFileName = new JsonObject();
                 response.setStatusCode(200); 
                 response.end(jsonObjectWithFileName.put("fileName", fileNameWithoutExtension).encodePrettily());
            });
        }

       public final void saveFile(RoutingContext rc, Vertx vertx) {
                 //TODO
       }
    }

And I use this class in my verticle like this:

    public class MyVerticle extends AbstractVerticle{

            private static final MyFile myFile = new MyFile();

            @Override
            public void start(Future<Void> startFuture) {
                final Router router = Router.router(vertx);
                final EventBus eventBus = vertx.eventBus();

                router.route("/getFile").handler(routingContext -> {
                    myFile.downloadFile(routingContext, vertx);
                });

        router.route("/saveFile").handler(routingContext -> {
                    myFile.saveFile(routingContext, vertx);
                });
            }
    }

My colleague tells me that it is not good to instantiate a class in a verticle and when I asked him why, he replied that it becomes stateful and I have doubts about what he says to me because I don't see how. And as I declared my MyFile class instance "static final" in my verticle, I want to say that I even gain in performance because I use the same instance for each incoming request instead of creating a new instance .

If it's bad to instantiate a class in a verticle, please explain why?

In addition I would like to know what is the interest of using 2 verticles for a treatment that only one verticle can do?

For example, I want to build a JsonObject with the data I select in my database, why send this data to another verticle knowing that this verticle does nothing but build the JsonObject and wait for it to answer me for sent the response to the client so that I can build this JsonObject in the verticle where I made my request and immediately sent the response to the client.I put you a pseudo code to see better :

public class MyVerticle1 extends AbstractVerticle{

    public void start(Future<Void> startFuture) {

        connection.query("select * from file", result -> {

            if (result.succeeded()) {
                List<JsonArray> rowsSelected = result.result().getResults();
                eventBus.send("adress", rowsSelected, res -> {
                    if (res.succeded()) {
                        routinContext.response().end(res.result().encodePrettily());
                    }
                });
            } else {
                LOGGER.error(result.cause().toString());
            }

        });

    }

}

public class MyVerticle2 extends AbstractVerticle{

    public void start(Future<Void> startFuture) {
        JsonArray resultOfSelect = new JsonArray();

        eventBus.consumer("adress", message -> {
            List<JsonArray> rowsSelected = (List<JsonArray>) message.body();
            rowsSelected.forEach(jsa -> {
                JsonObject row = new JsonObject();
                row.put("id", jsa.getInteger(0));
                row.put("name", jsa.getString(1));
                resultOfSelect.add(row);
            });

            message.reply(resultOfSelect);
        });
    }
}

I really do not see the point of making 2 verticles since I can use the result of my query in the first verticle without using the second verticle.

For me, EventBus is important for transmitting information to verticles for parallel processing.

Answer 1

bear in mind... the answers you're looking for are unfortunately very nuanced and will vary depending on a number of conditions (e.g. the experience of whoever is answering, design idioms in the codebase, tools/libraries at your disposal, etc). so there aren't an authoritative answers, just whatever suits you (and your co-workers).

My colleague tells me that it is not good to instantiate a class in a verticle and when I asked him why, he replied that it becomes stateful and I have doubts about what he says to me because I see not how.

your colleague is correct in the general sense that you don't want to have individual nodes in a cluster maintaining their own state because that will in fact hinder the ability to scale reliably. but in this particular case, MyFile appears to be stateless, so introducing it as a member of a Verticle does not automagically make the server stateful.

(if anything, i'd take issue with MyFile doing more than file-based operations - it also handles HTTP requests and responses).

And as I declared my MyFile class instance "static final" in my verticle, I want to say that I even gain in performance because I use the same instance for each incoming request instead of creating a new instance .

i'd say this goes to design preferences. there isn't any real "harm" done here, per se, but i tend to avoid using static members for anything other than constant literals and prefer instead to use dependency injection to wire up my dependencies. but maybe this is a very simple project and introducing a DI framework is beyond the complexity you wish to introduce. it totally depends on your particular set of circumstances.

In addition I would like to know what is the interest of using 2 verticles for a treatment that only one verticle can do?

again, this depends on your set of circumstances and your "complexity budget". if the processing is simple and your desire is to keep the design equally simple, a single Verticle is fine (and arguably easier to understand/conceptualize and support). in larger applications, i tend to create many Verticles along the lines of the different logical domains in play (e.g. Verticles for authentication, Verticles for user account functionality, etc), and orchestrate any complex processing through the EventBus.