Get result of completablefuture

JingJong :

I am using completablefuture to be returned from an async thread in springboot application. My implementation is below. From my understanding a new thread should be started for each item in list and should process parallely. I understand .get will block the execution but as it is parallely running still i dont see any improvement in performance. Any suggestions on below please to improve the performance?

ServiceA.java

@Autowired
ServiceB serviceb;


public List<String> getNames(List<Item> items) {
List<CompletableFuture<String>> list = new ArrayList<>();
List<String> returnList = new ArrayList<>();
for( Item item: items) {
  CompletableFuture<String> getItemName = serviceb.doProcess(item);
  list.add(getItemName):
}

for( CompletableFuture name : list) {
 returnList.add(name.get());
}
return returnList;
}

ServiceB.java

Class ServiceB {
@Async
Public CompletableFuture<String> doProcess(Item item)
{
   //do process
}

Beri :

You could call allOf to wait for all results. This will wait for all CompletableFuture to complete.

        List<String> returnList = new ArrayList<>(items.size());
        CompletableFuture<String>[] tasks = items.stream()
            .map(value-> serviceb.doProcess(value).thenApply(returnList::add))
            .toArray(CompletableFuture[]::new);
        // wait for all tasks to finish
        CompletableFuture.allOf(tasks).get(50, TimeUnit.SECONDS);
        // return the results
        return returnList;

Second solution would be to use an reactive approach like publisher/subscriber pattern (Spring WebFlux or JavaRx). This way your application would have little/no waiting operation. But this would affect your application architecture.

One Advice: In order to create an CompletableFuture use the constructor with ExecutorService in order to keep in check number of threads and have control over running threads or when application shuts down.