As per Microsoft (
https://docs.microsoft.com/en-us/aspnet/signalr/overview/getting-started/introduction-to-signalr)
The only relationship to WebSockets is that "SignalR uses the new WebSocket transport where available, and falls back to older transports where necessary." So yeah, just connecting to a SignalR service with a WebSocket is not going to cut it since that only covers the connection to the service.
That's because they are using a library that implements SignalR. It just also happens to support the use of WebSockets as a transport for SignalR.
Maybe. The java client for SignalR is here (
https://github.com/SignalR/java-client). Cannot help you there though, since I'm not a wrapper (pun alert, yes a bad pun, but a pun indeed). Could be that you can use it with JavaObjects.