Web Services, JSON, and XML

Abstract

Modern applications not only expose web service, they also consume other third-party web services. For example, your application may consume a Facebook or Twitter feed. Most modern web services are exposed using REST APIs that handle JSON payloads. A typical problem with calling web services is that they can block the caller and can result in blocking the server until a response is obtained or a timeout occurs. This is not a particularly good design because it can affect the throughput of the server and can result in missed SLAs. Play 2 has solved this problem by providing asynchronous, non-blocking APIs to invoke long-running tasks like an external web service. Play provides the play.libs.ws library to handle asynchronous web service calls. A call made by play.libs.ws returns CompletionStage . Later you can extract the response by using callback functions available in the CompletionStage interface. Essentially they are asynchronous callback methods. The caller makes a web service call and, once the response is available, the rest of the code runs. You will explore this in more detail later in this chapter.