CompletableFuture already completed with an exception

Question

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.

In which context do you need to do that? I think in a lot of contexts, just throwing the exception would do the job (e.g. with Spring @Async or with thenCompose()) — Didier L, Commented Mar 6, 2018 at 14:57
@DidierL I've got a method that executes quick tasks synchronously, but returns a CompletionStage. Why? Because the caller wants to validate input parameters synchronously before chaining asynchronous CompletionStages after it, and it needs any exceptions thrown by precondition validation to get handled by exceptionally(). — Gili, Commented Mar 6, 2018 at 19:46

M. Justin · Accepted Answer · 2019-08-21 23:20:36Z

32

Unlike Java 9 and later, Java 8 does not provide a static factory method for this scenario. The default constructor can be used instead:

CompletableFuture<T> future = new CompletableFuture<>();
future.completeExceptionally(exception);

M. Justin

18.7k9 gold badges117 silver badges146 bronze badges

answered Mar 5, 2018 at 18:15

Gili

88.7k101 gold badges405 silver badges711 bronze badges

Add a comment |

Didier L · Accepted Answer · 2018-03-27 12:42:26Z

16

answered Mar 27, 2018 at 12:42

Didier L

20.2k10 gold badges66 silver badges111 bronze badges

Add a comment |

2 Answers 2