All the discussions on the RESTful web services that we have had so far were based on the synchronous request and response model. When a client invokes a RESTful web API synchronously, the server keeps the request handling thread engaged till its request is processed. In this case, the entire request is processed in a single thread on the server. This model works if the request processing is finished quickly. The problem starts when a request takes more time to finish. In such a case, the thread used by the container to handle the long running request will remain busy till the processing is over. This may adversely affect the scalability of the application when the load (concurrent requests) increases because the server will not have enough threads in the pool to handle the incoming requests. The asynchronous processing feature in JAX-RS solves this by processing the long running requests asynchronously, thereby releasing the thread that is handling the...