RxJava: Is there an Observable.cachedDefer() operator, or some equivalent? - reactive-programming

Question

Is there a safe way to defer the creation of an Observable<T>, but upon creation cache it for a period of time before it must create it again?
Observable.cachedDefer(() -> createExpensiveFiniteObservable().cache(), 5, TimeUnit.MINUTES);
I have data sets that are expensive to construct and I want them cached long enough to support a process, but let them expire approximately between each run.

Answer 1

I've added the functionality to do this to rxjava-extras. The code below depends on rxjava-extras 0.6.8-RC2 or later (which is on Maven Central).
Run the main method below and you will see these results which seem to match the behaviour you desire (a reset of the cache whenever the time gap to next subscribe is >=5 seconds):
source emits Tue Oct 13 21:00:16 AEDT 2015
Tue Oct 13 21:00:16 AEDT 2015
Tue Oct 13 21:00:16 AEDT 2015
Tue Oct 13 21:00:16 AEDT 2015
Tue Oct 13 21:00:16 AEDT 2015
Tue Oct 13 21:00:16 AEDT 2015
source emits Tue Oct 13 21:00:31 AEDT 2015
Tue Oct 13 21:00:31 AEDT 2015
Tue Oct 13 21:00:31 AEDT 2015
Tue Oct 13 21:00:31 AEDT 2015
Tue Oct 13 21:00:31 AEDT 2015
Tue Oct 13 21:00:31 AEDT 2015
source emits Tue Oct 13 21:00:46 AEDT 2015
Tue Oct 13 21:00:46 AEDT 2015
Tue Oct 13 21:00:46 AEDT 2015
...
Main method:
public static void main(String[] args) throws InterruptedException {
Observable<Date> source = Observable
.defer(() ->
Observable
.just(new Date())
.doOnNext(
d -> System.out.println("source emits " + d)));
CloseableObservableWithReset<Date> cached =
Obs.cache(source, 5, TimeUnit.SECONDS, Schedulers.computation());
Observable<Date> o = cached
.observable()
.doOnSubscribe(() -> cached.reset());
for (int i = 0; i < 30; i++) {
o.doOnNext(System.out::println).subscribe();
Thread.sleep((i % 5 + 1)*1000);
}
cached.close();
}
Note that to reset the cache on every emission as well then where you see
.doOnSubscribe(() -> cached.reset())
put
.doOnSubscribe(() -> cached.reset())
.doOnNext(x -> cached.reset())