How to handle null?

Learn how to execute specific actions on null items

Unis are often used to represent asynchronous operations, like making an HTTP call. So, it’s not rare to need to add a timeout or a deadline on this kind of operation. If we don’t get a response (receive an item in the Mutiny lingo) before that deadline, we consider that the operation failed. We can then recover from this failure by using a fallback value, retrying, or any other failure handling strategy.

To configure a timeout use Uni.ifNoItem().after(Duration):

Uni<String> uniWithTimeout = uni
        .ifNoItem().after(Duration.ofMillis(100))
        .recoverWithItem("some fallback item");

When the deadline is reached, you can do various actions. First you can simply fail:

Uni<String> uniWithTimeout = uni
        .ifNoItem().after(Duration.ofMillis(100)).fail();

A TimeoutException is propagated in this case. So you can handle it specifically in the downstream:

Uni<String> uniWithTimeout = uni
    .ifNoItem().after(Duration.ofMillis(100)).fail()
    .onFailure(TimeoutException.class).recoverWithItem("we got a timeout");

You can also pass a custom exception:

Uni<String> uniWithTimeout = uni
    .ifNoItem().after(Duration.ofMillis(100)).failWith(() -> new ServiceUnavailableException());

Failing and recovering might be inconvenient. So, you can pass a fallback item or Uni directly:

Uni<String> uniWithTimeout = uni
        .ifNoItem().after(Duration.ofMillis(100)).recoverWithItem(() -> "fallback");
Uni<String> uniWithTimeout = uni
        .ifNoItem().after(Duration.ofMillis(100)).recoverWithUni(() -> someFallbackUni());