Combine a list of Observables and wait until all completed in java

Combine a list of Observables and wait until all completed in java

To combine a list of Observables and wait until all of them have completed in Java using RxJava, you can use the Observable.zip operator along with the Observable.concat operator. Here's a step-by-step guide on how to do this:

  • Add the RxJava dependency to your project if you haven't already. You can do this by including the following Maven dependency in your pom.xml:
<dependency> <groupId>io.reactivex.rxjava3</groupId> <artifactId>rxjava</artifactId> <version>3.x.x</version> <!-- Replace with the latest version --> </dependency>
  • Import the necessary classes in your Java code:
import io.reactivex.rxjava3.core.Observable; import io.reactivex.rxjava3.schedulers.Schedulers;
  • Create a list of Observables that you want to combine:
List<Observable<String>> observables = new ArrayList<>(); observables.add(Observable.fromCallable(() -> { // Simulate some asynchronous operation Thread.sleep(2000); return "Observable 1"; }).subscribeOn(Schedulers.io())); observables.add(Observable.fromCallable(() -> { // Simulate another asynchronous operation Thread.sleep(1000); return "Observable 2"; }).subscribeOn(Schedulers.io()));

In this example, we have two Observables that simulate asynchronous operations. You can replace these with your actual Observables.

  • Combine and wait for all Observables to complete:
Observable<String> combinedObservable = Observable.concat(observables) .toList() .flatMapObservable(list -> Observable.zip( observables, objects -> Arrays.stream(objects).map(Object::toString).collect(Collectors.toList()), false, observables.size() )); combinedObservable.subscribe( result -> { System.out.println("Combined result: " + result); }, throwable -> { System.err.println("Error: " + throwable.getMessage()); }, () -> { System.out.println("All observables have completed."); } );

In this code:

  • We use Observable.concat to merge the Observables in the observables list.
  • We convert the merged Observables into a single list using .toList().
  • We use Observable.zip to combine the results from all Observables into a single Observable. The zip operator takes the list of Observables, a function to combine the results, and the number of items to emit before completing.
  • We subscribe to the combinedObservable to handle the results or errors and receive a completion notification when all Observables have completed.

This code combines a list of Observables and waits until all of them have completed before processing the combined result.

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