JAX-RS is an API designed to give a portable and standard way for building RESTful web services in Java. This is one of the most used technologies for data transporting between different applications that uses some network (internet included) for communication.

One of the coolest features introduced by the 2.1 release is Server-Sent Events (SSE), which will be covered in this recipe. SSE is a specification created by HTML5 where it has established a channel between server and client, one way only from server to client. It is a protocol that transports a message containing some data.