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In RxJava : Highlighting of an unexpected difference between flatmap and concatmap when the incoming stream has only one element
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| import java.util.*; | |
| import java.util.function.*; | |
| import rx.Observable; | |
| import rx.functions.Func1; | |
| import rx.observers.TestSubscriber; | |
| import static rx.Observable.*; | |
| import static rx.internal.util.UtilityFunctions.identity; | |
| import static rx.schedulers.Schedulers.*; | |
| public class FlatMapVSConcatMapTest { | |
| private static final int trialNb = 10; | |
| private static final int testSize = 10000; // the greater the size, the more chances to have failures | |
| private FlatMapVSConcatMapTest() { | |
| } | |
| public static void main(String[] args) { | |
| System.out.print("With ConcatMap : "); | |
| testLoop(FlatMapVSConcatMapTest::initIntFlowWithConcatMap); | |
| System.out.print("With FlatMap : "); | |
| testLoop(FlatMapVSConcatMapTest::initIntFlowWithFlatMap); | |
| } | |
| private static void testLoop(Function<Integer, Observable<Integer>> intFlowProducer) { | |
| TestSubscriber<String> subscriber = new TestSubscriber<>(); | |
| range(0, trialNb) // | |
| .flatMap(any -> initTestFlowWithZip(intFlowProducer)) // | |
| .filter(identity()) // | |
| .count() // | |
| .map(count -> "run " + trialNb + ", failures : " + (trialNb - count)) // | |
| .doOnNext(System.out::println) // | |
| .subscribe(subscriber); | |
| subscriber.awaitTerminalEvent(); | |
| } | |
| private static Observable<? extends Boolean> initTestFlowWithZip(Function<Integer, Observable<Integer>> intFlowProducer) { | |
| Observable<Integer> flow1 = intFlowProducer.apply(testSize); | |
| Observable<Integer> flow2 = intFlowProducer.apply(testSize); | |
| return Observable.zip(flow1, flow2, Objects::equals).all(identity()); | |
| } | |
| private static Observable<Integer> initIntFlowWithFlatMap(int size) { | |
| return just(size)// here we have a reduce, but for the repro case, just will do the job : returning only one element | |
| .observeOn(io()) // because function retrieveFlowToMap performs io to init the returned observable | |
| .flatMap(FlatMapVSConcatMapTest::retrieveFlowToMap); | |
| } | |
| private static Observable<Integer> initIntFlowWithConcatMap(int size) { | |
| return just(size)// here we have a reduce, but for the repro case, just will do the job : returning only one element | |
| .observeOn(io()) // because function retrieveFlowToMap performs io to init the returned observable | |
| .concatMap(FlatMapVSConcatMapTest::retrieveFlowToMap); | |
| } | |
| private static Observable<Integer> retrieveFlowToMap(int size) { | |
| return range(0, size) // here we init the flow from a custom OnSubscribe, but for the repro case, range will do the job | |
| .subscribeOn(io()) // because call to request() in our custom OnSubscribe performs io | |
| .observeOn(computation()); // because we then perform computations on the returned data | |
| } | |
| private static Observable<? extends Boolean> initTestFlowWithOrderCheck(Function<Integer, Observable<Integer>> intFlowProducer) { | |
| Observable<Integer> flow = intFlowProducer.apply(testSize); | |
| return flow.all(new Func1<Integer, Boolean>() { | |
| private int previous = -1; | |
| @Override | |
| public Boolean call(Integer integer) { | |
| boolean increasing = previous < integer; | |
| previous = integer; | |
| return increasing; | |
| } | |
| }); | |
| } | |
| } |
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Typical output of the main :