In addition to the traditional pull model of getting HTML displayed in a browser when querying a service, most web browsers now support bidirectional communication via WebSockets so that servers can push data without the user having to query for it first. Once a socket is established between client and server, the communication can stay open for further interaction, unlike the HTTP protocol. Modern web apps are using this feature more and more to push data from streams reactively.

As a reminder, a WebSocket is a protocol providing bidirectional communication over a single TCP connection, in contrast to the traditional one-way, stateless communication of HTTP (either a request or a response). Let's look at the support that Play provides in this area and demonstrate in a short example how to establish a WebSocket communication between the Play server and a client browser.

As we have already created a ch9samples Play project at the beginning...