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I'm new to RxJava and I'm trying to understand the best/recommended way to perform long running tasks asynchronously (e.g. network requests). I've read through a lot of examples online but would appreciate some feedback.

The following code works (it prints 'one', 'two', then 'User: x' ... etc) but should I really be creating/managing Threads manually?

Thanks in advance!

public void start() throws Exception {
    System.out.println("one");
    observeUsers()
        .flatMap(users -> Observable.from(users))
        .subscribe(user -> System.out.println(String.format("User: %s", user.toString()));
    System.out.println("two");
}

Observable<List<User>> observeUsers() {
    return Observable.<List<User>>create(s -> {
        Thread thread = new Thread(() -> getUsers(s));
        thread.start();
    });
}

void getUsers(final Subscriber s) {
    s.onNext(userService.getUsers());
    s.onCompleted();
}

// userService.getUsers() fetches users from a web service.
arrwhidev
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1 Answers1

4

Instead of managing your own thread try using the defer() operator. Meaning replace observeUsers() with Observable.defer(() -> Observable.just(userService.getUsers())). Then you can use the RxJava Schedulers to control what threads are used during subscription and observation. Here's your code modified with the above suggestions.

Observable.defer(() -> Observable.just(userService.getUsers()))
        .flatMap(users -> Observable.from(users))
        .subscribeOn(Schedulers.newThread())
        .observeOn(Schedulers.trampoline())
        .subscribe(user -> System.out.println(String.format("User: %s", user.toString()));
kjones
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  • Also, instead of using `defer( )`, you can use `fromFunc0` from `RxJavaAsyncUtil`. See this answer: http://stackoverflow.com/a/31515376/1796309. Example: `Observable.fromFunc0(() -> userService.getUsers())`. Also, instead of `.flatMap(users -> Observable.from(users))` you can use `.flatMapIterable(users -> users)`. See this answer: http://stackoverflow.com/a/31580725/1796309 – Aleksandr Jul 24 '15 at 08:37