Automatically refresh external preview

[szolo]

The external preview for Platform designs should be automatically refreshed when the model changes.

Notes

• Probably needs some kind of javascript to connect with server
• Possible options include LiveReload, web sockets push, polling.
• Test Atmosphere

[Legioth]

I would recommend using plain websockets here, or maybe looking in to SSE (polyfilled for M$ browsers) as an alternative. Websockets require a little bit more client-side code than SSE (~10 lines of code vs ~5), but are instead slightly more straightforward on the server (especially if you want to do it "properly" with async servlets, though that might not be needed in this case).

LiveReload might also be an option if a servlet-based option is available (based on a very quick google search, the main Java implementation is based on Netty).

I don't think Atmosphere will be over very much help here based on the assumption that you won't need e.g. automatic fallback to another protocol. This is mostly needed in cases where there's e.g. a broken HTTP proxy in between that eats websockets, which I assume won't be a problem in this case?

[ripla]

Yeah, the use case is that most of the time it's just a localhost connection. In some cases it might be in the same local network. Websockets and SSE sound good.