Spring @Async with CompletableFuture

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Spring actually does all of the work behind the covers so you don’t have to create the CompletableFuture yourself.
Basically, adding the @Async annotation is as if you called your original method (without the annotation) like:

CompletableFuture<User> future = CompletableFuture.runAsync(() -> doFoo());

As for your second question, in order to feed it to an executor, you can specify the exectutor bean name in the value of the @Async annotation, like so:

    @Async("myExecutor")
    public CompletableFuture<User> findUser(String usernameString) throws InterruptedException {
        User fooResult = longOp(usernameString);
        return CompletableFuture.completedFuture(fooResult);
    }

The above would basically be the following as if you called your original method, like:

CompletableFuture<User> future = CompletableFuture.runAsync(() -> doFoo(), myExecutor);

And all of your exceptionally logic you would do with the returned CompletableFuture from that method.

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