Statelessness is being able to service the request independently without any requirement to remember any previous interactions.
In the example you have provided,
https://localhost:8080/UserManagement/rest/UserService/users/1
The restful service implementation that handles this request does not need to remember or know about any previous interaction with the client invoking the service.
All the information it needs to serve or process the request is provided and available in the request itself. It needs the user id, which it gets from the request URL itself and it is 1, it fetches the user details and returns the XML response.
For stateless services, if you need to change the response you would need to change the request details or the context values you pass in the request (so in addition to the URL it could also be the HTTP request headers like content type or Accepts, etc)