WebSockets are one of the biggest additions in Java EE 7. In this chapter, we will explore the new possibilities that they provide to a developer. In our ticket booking applications, we already used a wide variety of approaches to inform the clients about events occurring on the server side. These include the following:

All of them, besides JMS, were based on the assumption that the client will be responsible for asking the server about the state of the application. In some cases, such as checking whether someone else has not booked a ticket during our interaction with the application, this is a wasteful strategy; the server is in the position to inform clients when it is needed. What's more, it feels like the developer must hack the HTTP protocol to get a notification from a server to the client. This is a requirement that has to be implemented in most web applications, and therefore...