SSE, or server-sent events, is a means by which we can stream data from the server to the client. Typically, a REST request is very short-lived--make a connection, send the request, get a response, close the connection. Sometimes, though, the REST server may not have all of the data that the client wants at the time of the request (for example, reading data from another data source such as a log file or network socket). So, it would be nice to be able to push that data to the client as it becomes available. That's exactly what SSE allows us to do. We'll look into that in more detail later.
Finally, we start the server instance with a call to JettyHttpContainerFactory.createServer(). Since we need to be able to stop the server later, we capture the server instance, and store it in an instance variable. We call startServer() from onStartCommand() as...
