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Is there a cleaner way adapt a standard observer/listener service using RxJava?

I've been tinkering with wrapping an old style listener interface using RxJava. What i've come up with seems to work, but the usage of Observable.using feels a bit awkward.
The requirements are:
Only one subscription per id to the underlying service.
The latest value for a given id should be cached and served to new subscribers.
We must unsubscribe from the underlying service if nothing is listening to an id.
Is there a better way? The following is what I've got.
static class MockServiceRXAdapterImpl1 implements MockServiceRXAdapter {
PublishSubject<MockResponse> mockResponseObservable = PublishSubject.create();
MockService mockService = new MockService(mockResponse -> mockResponseObservable.onNext(mockResponse));
final ConcurrentMap<String, Observable<String>> subscriptionMap = new ConcurrentHashMap<>();
public Observable<String> getObservable(String id) {
return Observable.using(() -> subscriptionMap.computeIfAbsent(
id,
key -> mockResponseObservable.filter(mockResponse -> mockResponse.id.equals(id))
.doOnSubscribe(disposable -> mockService.subscribe(id))
.doOnDispose(() -> {
mockService.unsubscribe(id);
subscriptionMap.remove(id);
})
.map(mockResponse -> mockResponse.value)
.replay(1)
.refCount()),
observable -> observable,
observable -> {
}
);
}
}

You may use Observable.create
So code may look like this
final Map<String, Observable<String>> subscriptionMap = new HashMap<>();
MockService mockService = new MockService();
public Observable<String> getObservable(String id) {
log.info("looking for root observable");
if (subscriptionMap.containsKey(id)) {
log.info("found root observable");
return subscriptionMap.get(id);
} else {
synchronized (subscriptionMap) {
if (!subscriptionMap.containsKey(id)) {
log.info("creating new root observable");
final Observable<String> responseObservable = Observable.create(emitter -> {
MockServiceListener listener = emitter::onNext;
mockService.addListener(listener);
emitter.setCancellable(() -> {
mockServices.removeListener(listener);
mockService.unsubscribe(id);
synchronized (subscriptionMap) {
subscriptionMap.remove(id);
}
});
mockService.subscribe(id);
})
.filter(mockResponse -> mockResponse.id.equals(id))
.map(mockResponse -> mockResponse.value)
.replay(1)
.refCount();
subscriptionMap.put(id, responseObservable);
} else {
log.info("Another thread created the observable for us");
}
return subscriptionMap.get(id);
}
}
}

I think I've gotten it to work using .groupBy(...).
In my case Response.getValue() returns an int, but you get the idea:
class Adapter
{
Subject<Response> msgSubject;
ThirdPartyService service;
Map<String, Observable<Integer>> observables;
Observable<GroupedObservable<String, Response>> groupedObservables;
public Adapter()
{
msgSubject = PublishSubject.<Response>create().toSerialized();
service = new MockThirdPartyService( msgSubject::onNext );
groupedObservables = msgSubject.groupBy( Response::getId );
observables = Collections.synchronizedMap( new HashMap<>() );
}
public Observable<Integer> getObservable( String id )
{
return observables.computeIfAbsent( id, this::doCreateObservable );
}
private Observable<Integer> doCreateObservable( String id )
{
service.subscribe( id );
return groupedObservables
.filter( group -> group.getKey().equals( id ))
.doOnDispose( () -> {
synchronized ( observables )
{
service.unsubscribe( id );
observables.remove( id );
}
} )
.concatMap( Functions.identity() )
.map( Response::getValue )
.replay( 1 )
.refCount();
}
}

How to make Vertx MongoClient operation synchronous yet not blocking event loop in Java?

I am trying to save a new document to MongoDB using the Vertx MongoClient as follows:
MongoDBConnection.mongoClient.save("booking", query, res -> {
if(res.succeeded()) {
documentID = res.result();
System.out.println("MongoDB inserted successfully. + document ID is : " + documentID);
}
else {
System.out.println("MongoDB insertion failed.");
}
});
if(documentID != null) {
// MongoDB document insertion successful. Reply with a booking ID
String resMsg = "A confirmed booking has been successfully created with booking id as " + documentID +
". An email has also been triggered to the shared email id " + emailID;
documentID = null;
return new JsonObject().put("fulfillmentText", resMsg);
}
else {
// return intent response
documentID = null;
return new JsonObject().put("fulfillmentText",
"There is some issues while booking the shipment. Please start afreash.");
}
The above code successfully writes the query jsonObject to MongoDB collection booking. However, the function which contains this code always returns with There is some issues while booking the shipment. Please start afreash.
This is happening probably because the MongoClient save() handler "res" is asynchronous. But, I want to return conditional responses based on successful save() operation and on failed save operation.
How to achieve it in Vertx Java?

Your assumption is correct, you dont wait for the async response from the database. What you can do, is to wrap it in a Future like this:
public Future<JsonObject> save() {
Future<JsonObject> future = Future.future();
MongoDBConnection.mongoClient.save("booking", query, res -> {
if(res.succeeded()) {
documentID = res.result();
if(documentID != null) {
System.out.println("MongoDB inserted successfully. + document ID is : " + documentID);
String resMsg = "A confirmed booking has been successfully created with booking id as " + documentID +
". An email has also been triggered to the shared email id " + emailID;
future.complete(new JsonObject().put("fulfillmentText", resMsg));
}else{
future.complete(new JsonObject().put("fulfillmentText",
"There is some issues while booking the shipment. Please start afreash."))
}
} else {
System.out.println("MongoDB insertion failed.");
future.fail(res.cause());
}
});
return future;
}
Then i assume you have and endpoint that eventually calls this, eg:
router.route("/book").handler(this::addBooking);
... then you can call the save method and serve a different response based on the result
public void addBooking(RoutingContext ctx){
save().setHandler(h -> {
if(h.succeeded()){
ctx.response().end(h.result());
}else{
ctx.response().setStatusCode(500).end(h.cause());
}
})
}

You can use RxJava 2 and a reactive Mongo Client (io.vertx.reactivex.ext.mongo.MongoClient)
Here is a code snippet:
Deployer
public class Deployer extends AbstractVerticle {
private static final Logger logger = getLogger(Deployer.class);
#Override
public void start(Future<Void> startFuture) {
DeploymentOptions options = new DeploymentOptions().setConfig(config());
JsonObject mongoConfig = new JsonObject()
.put("connection_string",
String.format("mongodb://%s:%s#%s:%d/%s",
config().getString("mongodb.username"),
config().getString("mongodb.password"),
config().getString("mongodb.host"),
config().getInteger("mongodb.port"),
config().getString("mongodb.database.name")));
MongoClient client = MongoClient.createShared(vertx, mongoConfig);
RxHelper.deployVerticle(vertx, new BookingsStorage(client), options)
.subscribe(e -> {
logger.info("Successfully Deployed");
startFuture.complete();
}, error -> {
logger.error("Failed to Deployed", error);
startFuture.fail(error);
});
}
}
BookingsStorage
public class BookingsStorage extends AbstractVerticle {
private MongoClient mongoClient;
public BookingsStorage(MongoClient mongoClient) {
this.mongoClient = mongoClient;
}
#Override
public void start() {
var eventBus = vertx.eventBus();
eventBus.consumer("GET_ALL_BOOKINGS_ADDRESS", this::getAllBookings);
}
private void getAllBookings(Message msg) {
mongoClient.rxFindWithOptions("GET_ALL_BOOKINGS_COLLECTION", new JsonObject(), sortByDate())
.subscribe(bookings -> {
// do something with bookings
msg.reply(bookings);
},
error -> {
fail(msg, error);
}
);
}
private void fail(Message msg, Throwable error) {
msg.fail(500, "An unexpected error occurred: " + error.getMessage());
}
private FindOptions sortByDate() {
return new FindOptions().setSort(new JsonObject().put("date", 1));
}
}
HttpRouterVerticle
// inside a router handler:
vertx.eventBus().rxSend("GET_ALL_BOOKINGS_ADDRESS", new JsonObject())
.subscribe(bookings -> {
// do something with bookings
},
e -> {
// handle error
});

rxjava - getting response and inserting diff parallelly

I am using rxjava for parallel processing of two requests using Observable.zip. What I am trying to do is , in one observable say response I am getting one response and in other observable say diff I am trying to get the response and save this difference in DB. The problem is I am not sure how to achieve my requirement as the diff observable is not getting completed if response observable gets the response
Here is what I am doing ...
public ServiceResponse getDummyResponse(ServiceRequest serviceRequest, String prodId){
Observable<ServiceResponse> subInfoDummyObservable = getDummyResonseGenericObservable();
Observable<ServicesDiff> reObservable = getServicesDiffGenericObservable(serviceRequest, prodId);
Observable<ServiceResponse> responseObservable = Observable.zip(
subInfoDummyObservable,
reObservable,
new Func2<ServiceResponse, ServicesDiff, ServiceResponse>() {
#Override
public ServiceResponse call(ServiceResponse serviceResponse, ServicesDiff diffResponse) {
return serviceResponse;
}
}
);
ServiceResponse serviceResponse = responseObservable.toBlocking().single();
return serviceResponse;
}
Observable<ServiceResponse> getDummyResonseGenericObservable() {
return GenericHystrixCommand.toObservable("getDummyResonseGenericObservable", "getDummyResonseGenericObservable", () -> new ServiceResponse(),(t) -> {return null;} );
}
Observable<ServicesDiff> getServicesDiffGenericObservable(ServiceRequest serviceRequest, String prodId) {
return GenericHystrixCommand.toObservable("getServicesDiffGenericObservable", "getServicesDiffGenericObservable", () -> getBothServiceResponses(serviceRequest, prodId),(t) -> {return null;} );
}
public ServicesDiff getBothServiceResponses(ServiceRequest serviceRequest, String prodId) {
Observable<String> service1ResponseObservable = getService1GenericObservable(prodId);
Observable<ServiceResponse> service2ResponseObservable = getService2GenericObservable(serviceRequest, prodId);
Observable<ServicesDiff> observable = Observable.zip(
service1ResponseObservable, service2ResponseObservable,
new Func2<String, ServiceResponse, ServicesDiff>() {
#Override
public ServicesDiff call(String service1Response, ServiceResponse service2Response) {
return aggregate(service1Response, service2Response); // never reaches this point**********
}
}
);
ServicesDiff response = observable.toBlocking().single();
return response;
}
I am inserting the diff to DB in aggregate method but it never reaches to aggregate at all. Please let me know what I am doing wrong here? Thanks.

Observable are a description of how to consume data. In your code sample, you don't subscribe, you don't actually consume the data. You just described how to request, but the subscribe part, the part that trigger the requests, is missing.
So if I rewrite a little your code:
class Aggregate {
Aggregate(String reponse, ServicesDiff diff) {
...
}
}
Observable<String> getService1GenericObservable(String prodId) {
...
}
Observable<ServicesDiff> getServicesDiffGenericObservable(ServiceRequest serviceRequest, String prodId) {
...
}
public Observable<Aggregate> getBothServiceResponses(ServiceRequest serviceRequest, String prodId) {
Observable<String> service1ResponseObservable = getService1GenericObservable(prodId);
Observable<ServiceResponse> service2ResponseObservable = getService2GenericObservable(serviceRequest, prodId);
return Observable<Aggregate> observable = Observable.zip(
service1ResponseObservable, service2ResponseObservable,
new Func2<String, ServiceResponse, ServicesDiff>() {
#Override
public ServicesDiff call(String service1Response, ServiceResponse service2Response) {
return aggregate(service1Response, service2Response);
}
}
);
}
You will just have to do this to access the result aggregate:
getBothServiceResponses(serviceRequest, prodId).subscribe(...)

Rxjava Android how to use the Zip operator

I am having a lot of trouble understanding the zip operator in RxJava for my android project.
Problem
I need to be able to send a network request to upload a video
Then i need to send a network request to upload a picture to go with it
finally i need to add a description and use the responses from the previous two requests to upload the location urls of the video and picture along with the description to my server.
I assumed that the zip operator would be perfect for this task as I understood we could take the response of two observables (video and picture requests) and use them for my final task.
But I cant seem to get this to occur how I envision it.
I am looking for someone to answer how this can be done conceptually with a bit of psuedo code.
Thank you

Zip operator strictly pairs emitted items from observables. It waits for both (or more) items to arrive then merges them. So yes this would be suitable for your needs.
I would use Func2 to chain the result from the first two observables.
Notice this approach would be simpler if you use Retrofit since its api interface may return an observable. Otherwise you would need to create your own observable.
// assuming each observable returns response in the form of String
Observable<String> movOb = Observable.create(...);
// if you use Retrofit
Observable<String> picOb = RetrofitApiManager.getService().uploadPic(...),
Observable.zip(movOb, picOb, new Func2<String, String, MyResult>() {
#Override
public MyResult call(String movieUploadResponse, String picUploadResponse) {
// analyze both responses, upload them to another server
// and return this method with a MyResult type
return myResult;
}
}
)
// continue chaining this observable with subscriber
// or use it for something else

A small example:
val observableOne = Observable.just("Hello", "World")
val observableTwo = Observable.just("Bye", "Friends")
val zipper = BiFunction<String, String, String> { first, second -> "$first - $second" }
Observable.zip(observableOne, observableTwo, zipper)
.subscribe { println(it) }
This will print:
Hello - Bye
World - Friends
In BiFunction<String, String, String> the first String the type of the first observable, the second String is the type of the second observable, the third String represents the type of the return of your zipper function.
I made a small example that calls two real endpoints using zip in this blog post

Here I have an example that I did using Zip in asynchronous way, just in case you´re curious
/**
* Since every observable into the zip is created to subscribeOn a diferent thread, it´s means all of them will run in parallel.
* By default Rx is not async, only if you explicitly use subscribeOn.
*/
#Test
public void testAsyncZip() {
scheduler = Schedulers.newThread();
scheduler1 = Schedulers.newThread();
scheduler2 = Schedulers.newThread();
long start = System.currentTimeMillis();
Observable.zip(obAsyncString(), obAsyncString1(), obAsyncString2(), (s, s2, s3) -> s.concat(s2)
.concat(s3))
.subscribe(result -> showResult("Async in:", start, result));
}
/**
* In this example the the three observables will be emitted sequentially and the three items will be passed to the pipeline
*/
#Test
public void testZip() {
long start = System.currentTimeMillis();
Observable.zip(obString(), obString1(), obString2(), (s, s2, s3) -> s.concat(s2)
.concat(s3))
.subscribe(result -> showResult("Sync in:", start, result));
}
public void showResult(String transactionType, long start, String result) {
System.out.println(result + " " +
transactionType + String.valueOf(System.currentTimeMillis() - start));
}
public Observable<String> obString() {
return Observable.just("")
.doOnNext(val -> {
System.out.println("Thread " + Thread.currentThread()
.getName());
})
.map(val -> "Hello");
}
public Observable<String> obString1() {
return Observable.just("")
.doOnNext(val -> {
System.out.println("Thread " + Thread.currentThread()
.getName());
})
.map(val -> " World");
}
public Observable<String> obString2() {
return Observable.just("")
.doOnNext(val -> {
System.out.println("Thread " + Thread.currentThread()
.getName());
})
.map(val -> "!");
}
public Observable<String> obAsyncString() {
return Observable.just("")
.observeOn(scheduler)
.doOnNext(val -> {
System.out.println("Thread " + Thread.currentThread()
.getName());
})
.map(val -> "Hello");
}
public Observable<String> obAsyncString1() {
return Observable.just("")
.observeOn(scheduler1)
.doOnNext(val -> {
System.out.println("Thread " + Thread.currentThread()
.getName());
})
.map(val -> " World");
}
public Observable<String> obAsyncString2() {
return Observable.just("")
.observeOn(scheduler2)
.doOnNext(val -> {
System.out.println("Thread " + Thread.currentThread()
.getName());
})
.map(val -> "!");
}
You can see more examples here https://github.com/politrons/reactive

zip operator allow you to compose a result from results of two different observable.
You 'll have to give am lambda that will create a result from datas emitted by each observable.
Observable<MovieResponse> movies = ...
Observable<PictureResponse> picture = ...
Observable<Response> response = movies.zipWith(picture, (movie, pic) -> {
return new Response("description", movie.getName(), pic.getUrl());
});

i have been searching for a simple answer on how to use the Zip operator, and what to do with the Observables i create to pass them to it, i was wondering if i should call subscribe() for every observable or not, non of these answers were simple to find, i had to figure it out by my self, so here is a simple example for using Zip operator on 2 Observables :
#Test
public void zipOperator() throws Exception {
List<Integer> indexes = Arrays.asList(0, 1, 2, 3, 4);
List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
Observable<Integer> indexesObservable = Observable.fromIterable(indexes);
Observable<String> lettersObservable = Observable.fromIterable(letters);
Observable.zip(indexesObservable, lettersObservable, mergeEmittedItems())
.subscribe(printMergedItems());
}
#NonNull
private BiFunction<Integer, String, String> mergeEmittedItems() {
return new BiFunction<Integer, String, String>() {
#Override
public String apply(Integer index, String letter) throws Exception {
return "[" + index + "] " + letter;
}
};
}
#NonNull
private Consumer<String> printMergedItems() {
return new Consumer<String>() {
#Override
public void accept(String s) throws Exception {
System.out.println(s);
}
};
}
the printed result is :
[0] a
[1] b
[2] c
[3] d
[4] e
the final answers to the questions that where in my head were as follows
the Observables passed to the zip() method just need to be created only, they do not need to have any subscribers to them, only creating them is enough ... if you want any observable to run on a scheduler, you can specify this for that Observable ... i also tried the zip() operator on Observables where they should wait for there result, and the Consumable of the zip() was triggered only when both results where ready (which is the expected behavior)

This is my implementation using Single.zip and rxJava2
I tried to make it as easy to understand as possible
//
// API Client Interface
//
#GET(ServicesConstants.API_PREFIX + "questions/{id}/")
Single<Response<ResponseGeneric<List<ResponseQuestion>>>> getBaseQuestions(#Path("id") int personId);
#GET(ServicesConstants.API_PREFIX + "physician/{id}/")
Single<Response<ResponseGeneric<List<ResponsePhysician>>>> getPhysicianInfo(#Path("id") int personId);
//
// API middle layer - NOTE: I had feedback that the Single.create is not needed (but I haven't yet spent the time to improve it)
//
public Single<List<ResponsePhysician>> getPhysicianInfo(int personId) {
return Single.create(subscriber -> {
apiClient.getPhysicianInfo(appId)
.subscribeOn(Schedulers.io())
.observeOn(Schedulers.io())
.subscribe(response -> {
ResponseGeneric<List<ResponsePhysician>> responseBody = response.body();
if(responseBody != null && responseBody.statusCode == 1) {
if (!subscriber.isDisposed()) subscriber.onSuccess(responseBody.data);
} else if(response.body() != null && response.body().status != null ){
if (!subscriber.isDisposed()) subscriber.onError(new Throwable(response.body().status));
} else {
if (!subscriber.isDisposed()) subscriber.onError(new Throwable(response.message()));
}
}, throwable -> {
throwable.printStackTrace();
if(!subscriber.isDisposed()) subscriber.onError(throwable);
});
});
}
public Single<List<ResponseQuestion>> getHealthQuestions(int personId){
return Single.create(subscriber -> {
apiClient.getBaseQuestions(personId)
.subscribeOn(Schedulers.io())
.observeOn(Schedulers.io())
.subscribe(response -> {
ResponseGeneric<List<ResponseQuestion>> responseBody = response.body();
if(responseBody != null && responseBody.data != null) {
if (!subscriber.isDisposed()) subscriber.onSuccess(response.body().data);
} else if(response.body() != null && response.body().status != null ){
if (!subscriber.isDisposed()) subscriber.onError(new Throwable(response.body().status));
} else {
if (!subscriber.isDisposed()) subscriber.onError(new Throwable(response.message()));
}
}, throwable -> {
throwable.printStackTrace();
if(!subscriber.isDisposed()) subscriber.onError(throwable);
});
});
}
//please note that ResponseGeneric is just an outer wrapper of the returned data - common to all API's in this project
public class ResponseGeneric<T> {
#SerializedName("Status")
public String status;
#SerializedName("StatusCode")
public float statusCode;
#SerializedName("Data")
public T data;
}
//
// API end-use layer - this gets close to the UI so notice the oberver is set for main thread
//
private static class MergedResponse{// this is just a POJO to store all the responses in one object
public List<ResponseQuestion> listQuestions;
public List<ResponsePhysician> listPhysicians;
public MergedResponse(List<ResponseQuestion> listQuestions, List<ResponsePhysician> listPhysicians){
this.listQuestions = listQuestions;
this.listPhysicians = listPhysicians;
}
}
// example of Single.zip() - calls getHealthQuestions() and getPhysicianInfo() from API Middle Layer
private void downloadHealthQuestions(int personId) {
addRxSubscription(Single
.zip(getHealthQuestions(personId), getPhysicianInfo(personId), MergedResponse::new)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(response -> {
if(response != null) {
Timber.i(" - total health questions downloaded %d", response.listQuestions.size());
Timber.i(" - physicians downloaded %d", response.listPhysicians.size());
if (response.listPhysicians != null && response.listPhysicians.size()>0) {
// do your stuff to process response data
}
if (response.listQuestions != null && response.listQuestions.size()>0) {
// do your stuff to process response data
}
} else {
// process error - show message
}
}, error -> {
// process error - show network error message
}));
}

You use the zip from rxjava with Java 8:
Observable<MovieResponse> movies = ...
Observable<PictureResponse> picture = ...
Observable<ZipResponse> response = Observable.zip(movies, picture, ZipResponse::new);
class ZipResponse {
private MovieResponse movieResponse;
private PictureResponse pictureResponse;
ZipResponse(MovieResponse movieResponse, PictureResponse pictureResponse) {
this.movieResponse = movieResponse;
this.pictureResponse = pictureResponse;
}
public MovieResponse getMovieResponse() {
return movieResponse;
}
public void setMovieResponse(MovieResponse movieResponse) {
this.movieResponse= movieResponse;
}
public PictureResponse getPictureResponse() {
return pictureResponse;
}
public void setPictureResponse(PictureResponse pictureResponse) {
this.pictureResponse= pictureResponse;
}
}

You can use .zipWith operator for Observable chains.
If uploadMovies() and uploadPictures() return Observable,
uploadMovies()
.zipWith(uploadPictures()) { m, p ->
"$m with $p were uploaded"
}
.subscribe { print(it) }

RxAndroid, combining multiple web calls

public List<Office> getOffices(){
final List<Office> offices = new ArrayList<>();
Observable observable = Observable.create(new Observable.OnSubscribe<Object>() {
#Override
public void call(Subscriber<? super Object> subscriber) {
for(String[] of : backToArray(downloadWebPage("http://api.ataxcloudapp.com/v1/franchise/listing/?location=" + zip))) {
offices.add(
new Office(
of,
backToArray(downloadWebPage("http://api.ataxcloudapp.com/v1/franchise/details/hours/" + of[0])).get(0),
downloadImage("https://www.ataxcloudapp.com/WebShared/uploads/franchises/" + of[0] + "/manager-photo.jpg?404=picture-placeholder.jpg"),
downloadImage("https://maps.googleapis.com/maps/api/staticmap?center=" + of[12] + ","+ of[13] +"&zoom=12&size=300x150&maptype=roadmap")
)
);
}
subscriber.onCompleted();
}
});
observable.subscribeOn(Schedulers.newThread())
.observeOn(AndroidSchedulers.mainThread())
.subscribe();
return offices;
}
The above solution kinda works, it takes very long to load results and its not consistent. the last 3 calls are all dependent on information given in the first call. What am i doing wrong here?

First, note that in order to be able to compose async methods, they all should return Observable<Something> and not directly Something.
So you should change your download methods to
public Observable<Image> downloadImage(String url)
public Observable<WebPage> downloadWebPage(String url)
Or create wrapper methods around them if you cannot change them.
Then you can use flatMap and zip for the getOffices method:
public Observable<Office> getOffices() {
return downloadWebPage("office-url")
.flatMap(new Func1<WebPage, Observable<Office>>() {
public Observable<Office> call(WebPage webPage) {
String url1 = "blah" + webPage.getInfo1();
String url2 = "blah" + webPage.getInfo2();
String url3 = "blah" + webPage.getInfo3();
return Observable.zip(
downloadWebPage(url1),
downloadImage(url2),
downloadImage(url3),
new Func3<WebPage, Image, Image, Office>() {
public Office call(WebPage p, Image img1, Image img2) {
return new Office(p.getInfo0(), img1, img2);
}
});
}
});
}