Vert.x 3，请求处理程序POST，异步CompletionStage或CompletableFuture

Question

class MyVerticle extends AbstractVerticle {

 void start ...

   router.get("/api/v1/mypostcall").handler(routingContext -> {
       ...
       // I have existing async code, which I want to plug here.
       CompletionStage<String> jsonCompletable = ...

       // How do I respond using the CompletionStage (or CompletableFuture) to VertX
       // so it does not block here ?
    }

I have also read about the vert.x context , but the routingContext is something else and the example is about unit tests ... Do you have any example of integration between Java CompletionStage or must I use RxJava ?

Answer 1

There nothing special with CompletableFuture . It's like any async api. Simple example, that follows vertx thread model. Computation happens on some computational context, and result writes on vertx event loop:

public static CompletionStage<String> calculateAsync()  {
    CompletableFuture<String> completableFuture = new CompletableFuture<>();
    Executors.newCachedThreadPool().submit(() -> {
        Thread.sleep(5000);
        completableFuture.complete("Hello");
        return null;
    });
    return completableFuture;
}

public static void main(String[] args) {
    Vertx vertx = Vertx.vertx();
    Router router = Router.router(vertx);
    Router.router(vertx).get("/api").handler(ctx -> {
        calculateAsync().whenComplete((result, e) -> vertx.runOnContext(none -> {
            ctx.response().end(result);
        }));

    });
    vertx.createHttpServer().requestHandler(router::accept).listen(8080);
}

Answer 2

If all your stages are non-blocking and follow the Vert.x threading model (meaning always use the event loop), just use the "handle" method from your completable future in which you write the response (routingContext.response().end(...)) or report a failure.

If you are integrating stages not following the Vert.x threading model, you can use https://github.com/cescoffier/vertx-completable-future that provides a way to always call the stage in the "right" thread.