We live in a small, wonderful world where everybody is interconnected and impatient! We are interconnected through technology and applications, such as social networks, Internet banking, telephones, chats, and so on. Likewise, our applications are interconnected; often, an application housed in India may need to query an external service hosted in Philadelphia to get some significant information.

We are impatient as we expect everything to be done in seconds; we get frustrated when we make an HTTP call to a remote service, and this blocks the processing unless the remote response is back. We cannot finish everything in milliseconds or nanoseconds, but we can process long-running tasks asynchronously or in a separate thread, allowing the user to work on something else.

To handle RESTful web service calls asynchronously, Spring offers two useful classes: AsyncRestTemplate and ListenableFuture. We can make an async call using the template and get Future back and then...