Play application's execution model

The streaming programming model provided by Play has been influenced by the execution model of Play applications, which itself has been influenced by the nature of the work a web application performs. So, let's start from the beginning: what does a web application do?

For now, our example application does the following: the HTTP layer invokes some business logic via the service layer, and the service layer does some computations by itself and also calls the database layer. It is worth noting that in our configuration, the database system, as implemented in Chapter 2, Persisting Data and Testing, runs on the same machine as the web application but this is, however, not a requirement. In fact, there are chances that in real-world projects, your database system is decoupled from your HTTP layer and that both run on different machines. It means that while a query is executed on the database, the web layer does nothing but wait for the response. Actually...