Implementing asynchronous web service clients

In this section, we're going to take a look at the basic usage of asynchronous JAX-RS client APIs. We're using InvocationCallback instances to react to completed and failed calls. We'll also see how to do invocation-chaining of asynchronous client requests with CompletableFuture.

Let's get started and switch to code. As usual, we prepared a small template project to get started. We'll be using a JUnit test to showcase the JAX-RS client APIs. We're going to set up the JAX-RS client instance and the JAX-RS webTarget instance for the previously implemented asynchronous service API. As you might remember, in the previous section, we used Fibonacci number calculations asynchronously. We'll rewrite the test using the asynchronous JAX-RS client APIs against our REST API.

Let's open the AsyncWebServiceClientIntegrationTest class and start our tests; the first test should be pretty easy. We want to construct an asynchronous request and we do this the way...