I am calling one async method inside for loop and adding future of it into a list. I am not sure why allOff is not waiting to complete all futures and returning partial result. Have a look of my code.
I have one overridden method
@Overide
@Async
CompletableFuture<someType> fetchData()
{
returns new CompletableFuture<someType>();
}
I am calling above method in a for loop with different instances.
get all beans which implments one interface which has mehod fetchData.
Map<String, SomeClass> allBeans =context.getBeansOfType(SomeClass.class);
List<SomeClass> list=
allBeans.values().stream().collect(SomeClass.toList());
for (SomeClass classInstance: list) {
classInstance.fetchData().thenApply(x->{
//Some DB persistence Call
futureList.add(x);
});
}
after that I am applying allOff so that all future can be completed but it is not waiting for all and main thread excuting rest of flow.
CompletableFuture<Void> combinedFutures = CompletableFuture.allOf(
futureList.toArray(new CompletableFuture[futureList.size()]));
CompletableFuture<List<futureResponse>> finalList=
combinedFutures.thenApply(v -> {
return futureList.stream().map(m ->
m.join()).collect(Collectors.toList());
});
finalList- in this List I want all the completed futures returned by fetch invocation.
In finalList I am always getting 2 objects but fetchData is getting run 5 times( based on number of instances), I saw the log after all of remaining async call are getting completed. Could someone help here.
Observation:- After putting main thread on sleep for 30 sec, I could see I have all 5 objects in the list. Could some one please tell why main thread is not waiting at allOff for all futures to complete.
IIUC, what you want to do can be done simpler by doing
CompletableFuture<List<FutureResponse>> = CompletableFuture.supplyAsync(() -> {
// start fetches and collect the individual futures
List<CompletableFuture> fetches =
allBeans.values().stream()
.map(SomeClass::fetchData)
.collect(toList());
// join all futures and return the list of the results
return fetches.stream()
.map(CompletableFuture::join)
.collect(toList());
}
I think you can't do it in a single stream (ie map to fetch, then immediately to join) because that might wait for the join before the next future is created.