I'd like to see an Android java example of how to sequence a chain of async (= nonblocking) RESTful Volley requests.
Is this what RxAndroid is used for?
If so, I'd like to see the example using RxAndroid.
If not, I'd still like to see a good example w/out diving into CALLBACK HELL!
I tried to do so but ended up in CBHell:
Need to send multiple Volley Requests - in a sequence
I want my result from my 1st request to be used in the 2nd request. Then the result from the 2nd request I want used in the 3rd request. Please, how do I chain such Volley requests?
You could use Rx to chain multiple requests by using the flatMap method.
flatMap requires you to return another Observable of the type of your chosing thus allowing you do something async with another type.
All of the examples below are made with the new rx v2. But all methods and mechanics also apply to v1
Example:
final MyVolleyApi api = new MyVolleyApi();
api.getName()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.flatMap(new Function<String, ObservableSource<Integer>>() {
#Override
public ObservableSource<Integer> apply(String name) throws Exception {
return api.getAgeForName(name);
}
})
.flatMap(new Function<Integer, ObservableSource<Date>>() {
#Override
public ObservableSource<Date> apply(Integer age) throws Exception {
return api.getYearOfBirthForAge(age);
}
})
.doOnError(new Consumer<Throwable>() {
#Override
public void accept(Throwable throwable) throws Exception {
// handle the exception that occurred during one of the api calls
}
})
.subscribe(new Consumer<Date>() {
#Override
public void accept(Date date) throws Exception {
// do something with the 3rd argument here
}
});
This is the MyVolleyApi dummy class:
public class MyVolleyApi {
public Observable<String> getName() {
return Observable.just("Rx");
}
public Observable<Integer> getAgeForName(String name) {
return Observable.just(24);
}
public Observable<Date> getYearOfBirthForAge(int age) {
return Observable.just(new Date());
}
}
This could apply to anything, it's not volely specific at all
Related
I want to implement a logic using RxJava in my android application, which requires three parallel api calls. Only the third api call has a retry logic. If, after having three attempts, the success is achieved then a subsequent call will be made for the fourth api, else only the result of first and second api calls will be passed on to the subscriber.
I tried to achieve this using Zip operator but then got stuck with retry logic for third api call.
Observable<String> observable1 = Observable.just("A","B");
Observable<Integer> observable2 = Observable.just(1,2);
Observable<Boolean> observable3 = Observable.just(Boolean.TRUE, Boolean.FALSE);
Observable.zip(observable1, observable2, observable3, new Function3() {
#Override
public Object apply(String s, Integer integer, Boolean aBoolean) throws Exception {
if (aBoolean==null){
alphabets3.retry(3).doOnComplete(new Action() {
#Override
public void run() throws Exception {
// the result will never be used
}
});
}
return s+integer+aBoolean;
}
}).subscribe(new Observer<Object>() {
#Override
public void onSubscribe(Disposable d) {
}
#Override
public void onNext(Object o) {
Log.e("onNext-->", o.toString());
}
#Override
public void onError(Throwable e) {
}
#Override
public void onComplete() {
}
});
if any Observable failed in the Zip operator, Zip will fail the stream, the only way I know to achieve parallel execution and error handling with Zip, is to add onErrorResumeNext to each Observable, that map the error to a new model to deal with later .. and handling what you want to do in the zip mapping function ... for example
Obsevable.zip(
observable1.onErrorResumeNext{Observable.just(Model(it)},
observable2.onErrorResumeNext{Observable.just(Model(it)},
observable3.retryWhen {t is TimeOutException} //here you can add your retry logic
.onErrorResumeNext(t -> Observable.just(Model(t)),(m1 , m2, m3) -> Result())
I am new to android and I have a scenario where I want to get get data from multiple api. Let suppose api_a, api_b, api_c, api_d. These api are independent of each other but I want to show data from these api in a mix Recycler View (horizontal and vertical). So I want to make these api call in such a manner so that I can get every api data at a time so that i can display in recycler view.
I already using retrofit 2 but for that I had to chain them one by one which is very lengthy and I think this is not a feasible approach. I know little bit about RX JAVA ,but I only know how to make one request at a time. Please help
There are at least 2 ways to achieve this -
1) Using RxJava Zip operator (for parallel requests)
Get all the observables
Observable<ResponseType1> observable1 = retrofit.getApi_a();
Observable<ResponseType2> observable2 = retrofit.getApi_b();
Observable<ResponseType3> observable3 = retrofit.getApi_c();
Zip the observables to get a final observable
Observable<List<String>> result =
Observable.zip(observable1.subscribeOn(Schedulers.io()), observable2.subscribeOn(Schedulers
.io()), observable3.subscribeOn(Schedulers.io()), new Function3<ResponseType1, ResponseType2, ResponseType3, List<String>>() {
#Override
public List<String> apply(ResponseType1 type1, ResponseType2 type2, ResponseType3 type3) {
List<String> list = new ArrayList();
list.add(type1.data);
list.add(type2.data);
list.add(type3.data);
return list;
}
});
now subscribe on the resultant observable
result.observeOn(AndroidSchedulers.mainThread())
.subscribeWith(new Observer<List<String>>() {
#Override
public void onSubscribe(Disposable d) {
}
#Override
public void onNext(List<String> s) {
Log.d(TAG, "s is the list with all the data");
}
#Override
public void onError(Throwable e) {
Log.e(TAG, e.getMessage());
}
#Override
public void onComplete() {
}
});
2) Using RxJava flatMap() operator. (To request serially one after another)
This is simple chaining of requests
List<String> result = new ArrayList<>();
Disposable disposable = retrofit.getApi_a()
.subscribeOn(Schedulers.io())
.flatMap((Function<ResponseType1, ObservableSource<ResponseType2>>) response1 -> {
result.add(response1.data);
return retrofit.getApi_b();
})
.flatMap((Function<ResponseType2, ObservableSource<ResponseType3>>) response2 -> {
result.add(response2.data);
return retrofit.getApi_c();
})
.map(response3 -> {
result.add(response3.data);
return response3;
})
.observeOn(AndroidSchedulers.mainThread())
.subscribeWith(new DisposableObserver<Response3>() {
#Override
public void onNext(Response3 response3) {
Log.d(TAG, "result variable will have all the data");
}
#Override
public void onError(Throwable e) {
Log.e(TAG, e.getMessage());
}
#Override
public void onComplete() {
}
});
For combining multiple Observables you may want to consider the Merge operator.
This would allow you to combine the stream of multiple requests into a single Observable.
Merge will interleave them as they are emitted. If sequence matters, there is also Concat which will emit from each Observable before continuing with the next.
Rx Doc
Merge: http://reactivex.io/documentation/operators/merge.html
Concat: http://reactivex.io/documentation/operators/concat.html
Merge operator combines multiple observable into one
Set up Base URL of API:
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(Constants.BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.addCallAdapterFactory(RxJava2CallAdapterFactory.create())
.client(oktHttpClient.build())
.build();
Now setup two observables for the two network requests:
Observable<JsonElement> Observable1 = ApiClient.getApiService().getApi_1();
Observable<JsonElement> Observable2 = ApiClient.getApiService().getApi_2();
Now we use RxJava's mergemethod to combine our two Observables:
Observable.merge(Observable1, Observable2 )
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Observer<JsonElement>() {
#Override
public void onSubscribe(Disposable d) {
}
#Override
public void onNext(JsonElement value) {
Log.d("RESPONSE", "onNext:=======" + value);
}
#Override
public void onError(Throwable e) {
}
#Override
public void onComplete() {
Log.d("RESPONSE", "DONE==========");
}
});
I use RxAndroid library + Retrofit2.
I Have 2 post requests:
Get all category (return List == each String is category id)
Get ProductsByCategory (return List)
I need load all products and save to DB after start App.
When I create MainFragment I get all Categories:
restApiFactory.getProductService().getCategories(new CategoryRequest(initiatorId))
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new CategoriesHandler());
and Handle response:
#Override
public void onNext(CategoryResponse value) {
List<CategoryItem> categoryItems = value.getCategoryItems();
...
}
And then I need send another request(ProductsByCategory ) but I not understand how do it?
I can send it in foreach:
for (CategoryItem categoryItem : categoryItems) {
Observable<Products> product = ProductsByCategory...
}
or maby there is some Observable merge ....
I do not know. In general, how to do this? two requests to the server. one will return the list of id and the second product on these id.
You can achieve this by using flaMap in rxjava
This is example demonstrate snippet how to implement it
api.serviceA()
.flatMap(new Func1<FooA, Observable<FooB>>() {
#Override
public Observable<FooB> call(FooA fooA) {
// code to save data from service A to db
// call service B
return api.serviceB();
}
})
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Subscriber<FooB>() {
#Override
public void onCompleted() {
}
#Override
public void onError(Throwable e) {
}
#Override
public void onNext(FooB fooB) {
// code to save data from service B to db
}
});
You can use an Iterable, call api with CategoryItem and then use toList() in order to obtain a list of ProductsByCategory.
I am using RxJava on Android to perform a login operation.
I need to pass in a username, password and a boolean flag. The username and password and sent to a server for verification and once a response is returned I need to use the flag to determine what to do next.
Since the login operation is asynchronous, I want to ensure that when the response returns that I will still have access to the username, password and flag that I passed in at the beginning.
Here is the initial way I coded this up that I believe has problems:
public Observable<Result> execute1(final String username, final String password, final boolean shouldSaveUsername) {
return mLoginNetwork
.loginWithCredentials(username, password)
.map(new Func1<Response<Void>, LoginObject>() {
#Override
public LoginObject call(Response<Void> response) {
if (!response.isSuccessful()) {
Exceptions.propagate(new HttpException(response));
}
return new LoginObject(username, password, shouldSaveUsername);
}
})
.doOnNext(new Action1<LoginObject>() {
#Override
public void call(LoginObject loginObject) {
if (loginObject.shouldSaveUsername) {
saveUsername(username);
}
}
})
.flatMap(new Func1<Entitlement, Observable<Result>>() {
#Override
public Observable<Result> call(LoginObject loginObject) {
return mNetwork
.fetchSomething();
}
});
}
When I call execute1() it returns an Observable which I cache and then subscribe to. If an Android configuration change occurs I unsubscribe from the Observable but keep it in a cache. Once the configuration change is complete I take the Observable out of the cache and resubscribe to it. When I resubscribe the loginWithCredentials call would need to be made again, but when it returns the username, password and boolean flag would no longer exist and therefore I wouldn't be able to use them in my chain which is a problem.
So, how to solve this issue?
I need a way for the input data to the Observable to become part of the Observable so that when I cache the Observable the input data is also cached.
Here is a proposed solution below:
public Observable<Result> execute2(String username, String password, boolean shouldSaveUsername) {
return Observable
.just(new LoginData(username, password, shouldSaveUsername))
.flatMap(new Func1<LoginData, Observable<LoginData>>() {
#Override
public Observable<?> call(final LoginData loginData) {
return mLoginNetwork
.loginWithCredentials(loginData.getUsername(), loginData.getPassword())
.map(new Func1<Response<Void>, LoginData>() {
#Override
public LoginData call(Response<Void> response) {
if (!response.isSuccessful()) {
Exceptions.propagate(new HttpException(response));
}
return loginData;
}
});
}
})
.doOnNext(new Action1<LoginData>() {
#Override
public void call(LoginData loginData) {
if (loginData.shouldSaveUsername) {
saveUsername(username);
}
}
})
.flatMap(new Func1<LoginData, Observable<Result>>() {
#Override
public Observable<Result> call(LoginData loginData) {
return mNetwork
.fetchSomething();
}
});
}
What I'm attempting to do is to make the input data part of the stream right away by using Observable.just() to take the input data and make it into an Observable and then let the rest of the downstream operations receive it as an input. I assume that if I now cache the observable and resubscribe later that the input data is now embedded in my observable and can be accessed in any of the operators later.
Have I solved my problem in my proposed solution in a "normal" RxJava / functional way? Are there better ways to approach this problem?
The username/password/save-flag are passed in to execute1() as parameters, marked as final. Then, in your anonymous nested classes, you make explicit references to those values, "closing over" them. The resulting observable chain has everything bound to it that it needs in order to operate.
Subscribing to the observable again will use the original username/password/save-flag.
I've been wondering what's the best way to tackle the issue of token refresh.
I'm connecting to an API which supplies me with a auth-token, if sometime time during the calls i get a INVALID_AUTH i need to re-authenticate.
So for the naive implementation i did this
#SuppressWarnings("unchecked")
#Override
public Observable<User> getUsers() {
return runCommandAndrefreshAuthIfNecessary(new RequestCommand() {
#Override
public Observable create() {
return createService(UsersApi.class).getUsers();
}
});
}
private Observable runCommandAndrefreshAuthIfNecessary(final RequestCommand command) {
return command.create()
.onErrorResumeNext(new Func1<Throwable, Observable<?>>() {
#Override
public Observable<?> call(Throwable throwable) {
return handleRefreshToken(command);
}
});
}
private Observable<?> handleRefreshToken(final RequestCommand command) {
return refreshToken().flatMap(new Func1<Boolean, Observable<?>>() {
#Override
public Observable<?> call(Boolean aBoolean) {
return command.create();
}
});
}
As you can see i'm just wrapping the retrofit command, if i get an error i run refreshToken(), the token refreshes and i run the retrofit command again, so finally the Observable is passed back to the subscriber. Works as expected.
The thing i'm struggling with, is what happens i a multiple calls are made, for example, i'm calling getUsers and getFlags one after another. both of them get the INVALID_AUTH, currently both of the fire refreshToken(), which is bad.
i'm looking for a rx-java way to manage the calls, meaning after the first call of getUsers fires refreshToken, any call after that needs to wait for the refreshToken to end, only then fire the retrofit command.
Any suggestion will be appreciated.
You can use .cache() on the Observable for the token refreshing:
http://reactivex.io/documentation/operators/replay.html