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passing responses between observables in RxJava/RxAndroid

I have this code :
getLocationObservable() // ---> async operation that fetches the location.
// Once location is found(or failed to find) it sends it to this filter :
.filter(location -> { // ---> I want to use this location in the the onNext in the end
after finishing some calculation here, I either return 'true' and continue
to the next observable which is a Retrofit server call, or simply
return 'false' and quit.
})
.flatMap(location -> getRetrofitServerCallObservable( location )
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread()))
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(
new Observer<MyCustomResponse>() {
#Override
public void onSubscribe(Disposable d) {
_disposable = d;
}
#Override
public void onNext(MyCustomResponse response) {
// I want to be able to use the `location` object here
}
#Override
public void onError(Throwable e) {
}
#Override
public void onComplete() {
}
});
I want to be able to use the location object from line 3(first observable), in the "onNext" that is trigerred by the second observable.
I can't manage to work it out.. any help would be much appreciated.

Instead of
getRetrofitServerCallObservable( location )
you could map the result to be a Pair (from your favourite library) of the response and the location:
getRetrofitServerCallObservable( location ).map(response -> Pair.create(location, response))
Then, in your onNext, you'd be receiving Pair<Location,MyCustomResponse> instances.
If you don't want to use a Pair class, you could use Object[], but if you do, please don't tell me about it :P

RxJava block stream until other observer finish

I am getting a Flowable from one method called getAlldata()
and this method will get the data from the server and then modify the data that been returned base on the data that had been stored in the DB.
So the process of this method goes like this:
getdata from the server
doOnNext for each item get the id
get the local data by id.
modify the current item
The problem is:
the result will be return before actully the modification of the data in doOnNext() since getting the local data from the DB is another observable.
Question
how can I delay stream until the other observable that is on doOnNext() completes?
The codes
private Flowable<List<MyModule>> getAlldata() {
return remoteDataSource
.getData().flatMap(data -> Flowable.fromIterable(data))
.doOnNext(new Consumer<MyModule>() {
#Override
public void accept(MyModule singleItem) throws Exception {
localDataSource.getData(singleItem.getId())
.firstElement().toFlowable()
.subscribe(new Consumer<Optional<MyModule>>() {
#Override
public void accept(Optional<MyModule> itemOptional) throws Exception {
if (itemOptional.isPresent()) {
// modify the item
}
}
});
}
})
.distinct()
.sorted(ProductsRepository.this::sortItems)
.toList().toFlowable();
}

Use flatmap operator instead of doOnNext() which get the singleItem as a parameter and throw an observable of the type localdatabase. so now you can map the response instead of making your Observable wait.
Observable<ModuleData> obs = remoteDataSource
.getData().flatMapIterable(data ->data)
.flatMap(singleItem->localDataSource.getData(singleItem.getId()))
.distinct()
.sorted(ProductsRepository.this::sortItems)
.toList().toFlowable();

Exiting out of the iteratable Observable upon successful response

I have a scenario in which I've to bridge the nonreactive code with Reactive Code.
Consider the following scenario.
I have a list of 3 URLs in an ArrayList. I want to call each URL in the order they are inside the ArrayList. I can call only 1 URL at a time. If the first URL returns a successful Response, I want to call onComplete() and don't wanna execute the remaining URL. However, if the response is an error, I want to execute the next URL in the list. I don't want RxJava to call flatMap for the next URL unless I get an error response for the previous URL. Due to my primitive understanding of RxJava, I couldn't figure out a way to achieve this.
What I planned to do something like this:
Observable.fromIteratable(urlList)
.subscribeOn(Schedulars.io())
.flatMap(new Func(String url, String data) {
SomeNetworkLibrary.getData(url)
.OnResponse(new NewResponse() {
public void onSuccess(String dataFromInternet) {return dataFromInternet;}
public void onError(String errorMessage) {return errorMessage;)
})
// wait until we have response from the network call above and then return
// I don't know what will be the cleanest and efficient way of waiting here.
});
TLDR;
I don't want flatMap() to be called before the results from the previous flatMap() have been returned.
How can I do that?

You can turn the network api call into an Observable and then use take(1) after the flattening:
Observable.fromIteratable(urlList)
.subscribeOn(Schedulars.io())
.concatMapDelayError((String url, String data) -> {
return Observable.create(emitter -> {
SomeNetworkLibrary.getData(url)
.OnResponse(new NewResponse() {
public void onSuccess(String dataFromInternet) {
emitter.onNext(dataFromInternet);
// don't call emitter.onComplete() so that
// concatMapDelayError doesn't switch to the next source
}
public void onError(String errorMessage) {
emitter.onError(errorMessage);
}
);
});
// wait until we have response from the network call above and then return
// I don't know what will be the cleanest and efficient way of waiting here.
})
.take(1);

RXJava2: correct pattern to chain retrofit requests

I am relatively new to RXJava in general (really only started using it with RXJava2), and most documentation I can find tends to be RXJava1; I can usually translate between both now, but the entire Reactive stuff is so big, that it's an overwhelming API with good documentation (when you can find it). I'm trying to streamline my code, an I want to do it with baby steps. The first problem I want to solve is this common pattern I do a lot in my current project:
You have a Request that, if successful, you will use to make a second request.
If either fails, you need to be able to identify which one failed. (mostly to display custom UI alerts).
This is how I usually do it right now:
(omitted the .subscribeOn/observeOn for simplicity)
Single<FirstResponse> first = retrofitService.getSomething();
first
.subscribeWith(
new DisposableSingleObserver<FirstResponse>() {
#Override
public void onSuccess(final FirstResponse firstResponse) {
// If FirstResponse is OK…
Single<SecondResponse> second =
retrofitService
.getSecondResponse(firstResponse.id) //value from 1st
.subscribeWith(
new DisposableSingleObserver<SecondResponse>() {
#Override
public void onSuccess(final SecondResponse secondResponse) {
// we're done with both!
}
#Override
public void onError(final Throwable error) {
//2nd request Failed,
}
});
}
#Override
public void onError(final Throwable error) {
//firstRequest Failed,
}
});
Is there a better way to deal with this in RXJava2?
I've tried flatMap and variations and even a Single.zip or similar, but I'm not sure what the easiest and most common pattern is to deal with this.
In case you're wondering FirstRequest will fetch an actual Token I need in the SecondRequest. Can't make second request without the token.

I would suggest using flat map (And retrolambda if that is an option).
Also you do not need to keep the return value (e.g Single<FirstResponse> first) if you are not doing anything with it.
retrofitService.getSomething()
.flatMap(firstResponse -> retrofitService.getSecondResponse(firstResponse.id)
.subscribeWith(new DisposableSingleObserver<SecondResponse>() {
#Override
public void onSuccess(final SecondResponse secondResponse) {
// we're done with both!
}
#Override
public void onError(final Throwable error) {
// a request request Failed,
}
});
This article helped me think through styles in how I structure RxJava in general. You want your chain to be a list of high level actions if possible so it can be read as a sequence of actions/transformations.
EDIT
Without lambdas you can just use a Func1 for your flatMap. Does the same thing just a lot more boiler-plate code.
retrofitService.getSomething()
.flatMap(new Func1<FirstResponse, Observable<SecondResponse> {
public void Observable<SecondResponse> call(FirstResponse firstResponse) {
return retrofitService.getSecondResponse(firstResponse.id)
}
})
.subscribeWith(new DisposableSingleObserver<SecondResponse>() {
#Override
public void onSuccess(final SecondResponse secondResponse) {
// we're done with both!
}
#Override
public void onError(final Throwable error) {
// a request request Failed,
}
});

Does this not work for you?
retrofitService
.getSomething()
.flatMap(firstResponse -> retrofitService.getSecondResponse(firstResponse.id))
.doOnNext(secondResponse -> {/* both requests succeeded */})
/* do more stuff with the response, or just subscribe */

RxJava callback for last onNext() execution finished

I'm new to RxJava. I would like to download some data for each TempoAccount entity from given collection and store it all in a map accountsWithProjects. When the code of last onNext(TempoAccount tempoAccount) is completed I'd like to call filterAccountsWithProjects(accountsWithProjects) method. Is there some simple way to achieve it?
private void getProjectsForEachTempoAccount(Collection<TempoAccount> tempoAccounts) {
final Map<TempoAccount, Collection<TempoProject>> accountsWithProjects =
new HashMap<>(tempoAccounts.size());
Observable<TempoAccount> accountsObservable = Observable.from(tempoAccounts);
accountsObservable
.compose(ObservableUtils.applySchedulers())
.subscribe(new ObserverAdapter<TempoAccount>() {
#Override
public void onError(Throwable e) {
view.notifyAboutError(e.getMessage());
}
#Override
public void onNext(TempoAccount tempoAccount) {
jira.requestProjectsInfoForTempoAccount(String.valueOf(tempoAccount.getId()))
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new ObserverAdapter<Collection<TempoProject>>() {
#Override
public void onError(Throwable e) {
view.notifyAboutError(e.getMessage());
}
#Override
public void onNext(Collection<TempoProject> projects) {
accountsWithProjects.put(tempoAccount, projects);
}
});
}
#Override
public void onCompleted() {
filterAccountsWithProjects(accountsWithProjects);
}
});
}
Problem: In the code above filterAccountsWithProjects(accountsWithProjects) is fired before all observables from onNext(TempoAccount tempoAccount) are completed.
Edit:
I want to create an Observable of such a type: Observable<Map<TempoAccount, Collection<TempoProject>>.
I have two observables given:
Observable<TempoAccount> accountsObservable = Observable.from(tempoAccounts)
Observable<Collection<TempoProject>> projectsForAccountObservable = jira.requestProjectsInfoForTempoAccount(TempoAccount account)
So my questions is: can I connnect them somehow and create the map having these two observables.

You should use the flatMap() function on your original stream to do the things you are currently doing in the onNext(). Also, you don't need to filter the stream in onComplete(). You could use filter() on the stream itself and deal with the problem in a more "Reactive" way.
Here is an example:
accountsObservable
.compose(ObservableUtils.applySchedulers())
.map(tempoAccount -> new Pair<TempoAccount, Collection<TempoProject>>(tempoAccount, fetchInfoAccountForTempoAccount(tempoAccount)))
.filter(pair -> hasProjects(pair))
.toMap(pair -> pair.first(), pair -> pair.second)
.subscribe(...)
EDIT:
Updated the suggested answer - you get the TempoAccounts, then you map each account to a Pair of account and collection of TempoProjects. You filter the pairs to see if you have any projects and then you use toMap() to create your desired result. Be aware, that to get toMap() working, your observables have to call onComplete() when the end of the stream is reached.