Search code examples
javacompletable-futurejava-10

CompletableFuture immediate failure

I'd like to create a CompletableFuture that has already completed exceptionally.

Scala provides what I'm looking for via a factory method:

Future.failed(new RuntimeException("No Future!"))

Is there something similar in Java 10 or later?

Solution

  • Java 9 provides CompletableFuture#failedFuture(Throwable) which

    Returns a new CompletableFuture that is already completed exceptionally with the given exception.

    that is more or less what you submitted

    /**
 * Returns a new CompletableFuture that is already completed
 * exceptionally with the given exception.
 *
 * @param ex the exception
 * @param <U> the type of the value
 * @return the exceptionally completed CompletableFuture
 * @since 9
 */
public static <U> CompletableFuture<U> failedFuture(Throwable ex) {
    if (ex == null) throw new NullPointerException();
    return new CompletableFuture<U>(new AltResult(ex));
}