Surprising behavior of Java 8 CompletableFuture exceptionally method

Question

I have encountered strange behavior of Java 8 CompletableFuture.exceptionally method. If I execute this code, it works fine and prints java.lang.RuntimeException

Answer 1

yes, the behavior is expected, but if you want the original exception which was thrown from one of the previous stages, you can simply use this

CompletableFuture future = new CompletableFuture<>();

future.completeExceptionally(new RuntimeException());

future.thenApply(v-> v).exceptionally(e -> {
        System.out.println(e.getCause()); // returns a throwable back
        return null;
});