When to use @Singleton annotation of Jersey?

Question

I am developing a RESTful Web Service and while reading the Jersey documentation I came across an annotation @Singleton

In my web service I am mostly re

Answer 1

There is actually a use case specified in the Jersey 2 manual for using the SseBroadcaster when serving Server-Sent events, it is covered in this provided example

The BroadcasterResource resource class is annotated with @Singleton annotation which tells Jersey runtime that only a single instance of the resource class should be used to serve all the incoming requests to /broadcast path. This is needed as we want to keep an application-wide single reference to the private broadcaster field so that we can use the same instance for all requests. Clients that want to listen to SSE events first send a GET request to the BroadcasterResource, that is handled by the listenToBroadcast() resource method.

Using the @Singleton, The application will only contain one SseBroadcaster for all incoming requests, one such broadcaster is enough to serve multiple clients, so it only needs to be instantiated once!

JAX-RS SSE API defines SseBroadcaster which allows to broadcast individual events to multiple clients.