Vertx中的异步性，列表在设置之前返回空

Question

In my MainVerticle I set the router

router.get("/persons").handler(ctx -> apiService.getPersons(ctx, client));

I want to call the same host twice, first I need to get a list of person ids and then call another method of the same host to get the person details. . So, in this code, I am doing a get call in another one. Because of asynchronicity, the personList is empty since Vertx does not wait the reply of the second call, the reply of the second call comes later but of course the personList is empty. In my test case, the iterator has two elements. How should I implement it in order to be sure that the list will be returned well set?

        public void getPersons(RoutingContext routingContext, WebClient client){
    logger.info("getpersons");
    routingContext.response().headers().add("content-type", "application/json");
    String wshost= ConfigUtils.getStringConfig(vertx,"personws.url");
    String url = wshost+"/persons";
    client.getAbs(url).send(response -> {
        try {
            if (response.succeeded() && response.result().statusCode()==200) {
                List<Person> personList = new ArrayList<Person>();
                logger.info("Server content " + response.result().bodyAsString());

                Iterator<Object> iterator = response.result().bodyAsJsonArray().iterator();
                while(iterator.hasNext()){
                    Object obj = iterator.next();
                    JsonObject jsonPerson = (JsonObject) obj ;
                    logger.debug("personId: {}", jsonPerson.getString("id"));
                    Person person = new Person();
                    person.setId(jsonPerson.getString("id"));

                    String url2 = wshost+"/persons/"+jsonPerson.getString("id");
                    logger.info("Calling ws to get person details for : {}", jsonPerson.getString("id"), url2);
                     client.getAbs(url2).send(response2 -> {
                        if (response2.succeeded() && response2.result().statusCode()==200) {

                            JsonObject jsonDetails = response2.result().bodyAsJsonObject();
                            person.setDetail(jsonDetails);
                            personList.add(person);
                            logger.info("person is {} ", person);
                            logger.info("iterator.hasNext():{}", iterator.hasNext());


                        }
                        else{
                            routingContext.response().setStatusCode(500);
                            routingContext.response().end(buildError("Failed to get json ", 600).encode());
                        }

                    });

                };
                logger.info("personList: {} ", personList);
                logger.info("personList size {} ", personList.size());
                routingContext.response().setStatusCode(200).end(new JsonArray(personList).toString());
            } else {
                logger.error("Cannot get persons");
                routingContext.response().setStatusCode(500);
                routingContext.response().end(buildError("Failed to get persons", 100).encode());
            }
        } catch (Exception e) {
            e.printStackTrace();
            routingContext.response().setStatusCode(500);
            routingContext.response().end(buildError("Exception in API- Failed to get get persons for fleet "+routingContext.request().headers().get("fleet"), 300).encode());
        }

    });

}

Answer 1

First of all, you don't call your host only twice. You call it n+1 times, per number of persons in your initial request.

Simplest way to achieve what you need is to count the number of persons you expect to get:

                int expected = response.result().bodyAsJsonArray().size();

                Iterator<Object> iterator = response.result().bodyAsJsonArray().iterator();
                while(iterator.hasNext()){
                    Object obj = iterator.next();
                    JsonObject jsonPerson = (JsonObject) obj ;
                    logger.debug("personId: {}", jsonPerson.getString("id"));
                    Person person = new Person();
                    person.setId(jsonPerson.getString("id"));

                    String url2 = wshost+"/persons/"+jsonPerson.getString("id");
                    logger.info("Calling ws to get person details for : {}", jsonPerson.getString("id"), url2);
                    client.getAbs(url2).send(response2 -> {
                        if (response2.succeeded() && response2.result().statusCode()==200) {

                            JsonObject jsonDetails = response2.result().bodyAsJsonObject();
                            person.setDetail(jsonDetails);
                            personList.add(person);
                            logger.info("person is {} ", person);
                            logger.info("iterator.hasNext():{}", iterator.hasNext());

                            // That's the last one
                            if (personList.size() == expected) {
                                // Only now complete the request
                                routingContext.response().setStatusCode(200).end(new JsonArray(personList).toString());
                            }
                        }
                        else{
                            routingContext.response().setStatusCode(500);
                            routingContext.response().end(buildError("Failed to get json ", 600).encode());
                        }

                    });

                };
                logger.info("personList: {} ", personList);
                logger.info("personList size {} ", personList.size());
               // Moved inside callback

Other way would be to use CompositeFuture: http://vertx.io/docs/vertx-core/groovy/#_concurrent_composition