Asynchronous timeouts with CompletableFutures in Java 8 and Java 9

Asynchronous timeouts with CompletableFutures in Java 8 and Java 9

Java 8 introduced CompletableFuture<T> as an enhancement to Future<T>. It is a new class which lets you express the flow of information from different tasks using a callback driven style. A CompletableFuture is used for defining computations on singular events, which is a different use case than computations on streams of events (e.g. Observable using RxJava). In this article, you will learn about the problem with timeouts in Java 8's CompletableFuture and the improvements that Java 9 brings.

Combining two services

For the purpose of this article, let's say you'd like to combine the result of two services over the network:

1. A best price finder for a flight route
2. An exchange service that converts USD to GBP

Both of these services will introduce a certain delay before responding back with a result. This is due to the costs of network communication with the service.

You could solve this problem by making use of CompletableFuture as follows (by default a CompletableFuture uses the common thread pool but this can be parametrised with an Executor using an overload of supplyAsync):

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