Typically, in http based client-server scheme, server always responds to a request. There is no way server can send anything (notification) without client request it. But there are use cases for server pushing the data to client without client requesting and hence Server-Push came into picture.
Jersey provides Server Push in the form of Server-Sent Events (SSE). The documentation says,
Server-Sent Events (SSE) is a mechanism that allows server to asynchronously push the data from the server to the client once the client-server connection is established by the client
Please note that the client needs to establish connection with the server first. You might call that first client request as Registration. Once the connection is established, the server can send/push data to client. The linked mention also has a working example as well.