completable-future

I have a doubt about this code: @Async public CompletableFuture<String> doFoo() { CompletableFuture<String> fooFuture = new CompletableFuture<>(); try { String fooResult = longOp(); fooFuture.complete(fooResult); } catch (Exception e) { fooFuture.completeExceptionally(e); } return fooFuture; } The question is: does doFoo return fooFuture only after longOp has finished (either correctly or exceptionally) and is therefore returning already completed futures or is Spring doing some magic and returning before executing the body? If the code is blocking on longOp(), how would you express that the

I can't get my head around the difference between thenApply( ) and thenCompose() . So, could someone provide a valid use case? From the Java docs: thenApply(Function<? super T,? extends U> fn) Returns a new CompletionStage that, when this stage completes normally, is executed with this stage's result as the argument to the supplied function. thenCompose(Function<? super T,? extends CompletionStage<U>> fn) Returns a new CompletionStage that, when this stage completes normally, is executed with this stage as the argument to the supplied function. I get that the 2nd argument of thenCompose

I have some CompletableFuture s and I want to run them in parallel, waiting for the first that returns normally . I know I can use CompletableFuture.anyOf to wait for the first to return, but this will return normally or exceptionally . I want to ignore exceptions. List<CompletableFuture<?>> futures = names.stream().map( (String name) -> CompletableFuture.supplyAsync( () -> // this calling may throw exceptions. new Task(name).run() ) ).collect(Collectors.toList()); //FIXME Can not ignore exceptionally returned takes. Future any = CompletableFuture.anyOf(futures.toArray(new CompletableFuture<?>

I have encountered strange behavior of Java 8 CompletableFuture.exceptionally method. If I execute this code, it works fine and prints java.lang.RuntimeException CompletableFuture<String> future = new CompletableFuture<>(); future.completeExceptionally(new RuntimeException()); future.exceptionally(e -> { System.out.println(e.getClass()); return null; }); But if I add another step in the future processing like thenApply , the exception type changes to java.util.concurrent.CompletionException with the original exception wrapped inside. CompletableFuture<String> future = new CompletableFuture<>()

I don't see an obvious way to handle an exception with an asynchronous result. For example, if I want to retry an async operation. I would expect something like this, however handleAsync doesn't do what you think it does - it runs the callbacks on another thread asynchronously. Returning a CompletionStage here is not correct. Jeopardy question of the day: thenApply is to thenCompose as exceptionally is to what? CompletionStage<String> cf = askPong("cause error").handleAsync((x, t) -> { if (t != null) { return askPong("Ping"); } else { return x; } }); Where askPong asks an actor: public

Consider the following code public class TestCompletableFuture { BiConsumer<Integer, Throwable> biConsumer = (x,y) -> { System.out.println(x); System.out.println(y); }; public static void main(String args[]) { TestCompletableFuture testF = new TestCompletableFuture(); testF.start(); } public void start() { Supplier<Integer> numberSupplier = new Supplier<Integer>() { @Override public Integer get() { return SupplyNumbers.sendNumbers(); } }; CompletableFuture<Integer> testFuture = CompletableFuture.supplyAsync(numberSupplier).whenComplete(biConsumer); } } class SupplyNumbers { public static

CompletableFuture.completedFuture() returns a CompletedFuture that is already completed with the given value. How do we construct a CompletableFuture that is already completed exceptionally? Meaning, instead of returning a value I want the future to throw an exception. I just found this: CompletableFuture<T> future = new CompletableFuture<>(); future.completeExceptionally(t); There is no static factory method, but the default constructor seems to do the job. Java 9 provides CompletableFuture.failedFuture​(Throwable ex) that does exactly that. 来源： https://stackoverflow.com/questions/49116855