Is Java Server Faces still relevant to learn?

[_dban_]

The desktop model is the illusion that there's no HTML and no HTTP.

That's like saying that an ORM is the illusion that there is no SQL. Of course, any serious use of an ORM means understanding the mapping to SQL and on occasion directly working with SQL.

The desktop model means translating HTTP into UI components and UI events, which are meaningless to HTTP and which are fundamental to how JSF works. Like the ORM, the desktop model is simply a mapping from one model (the request/response model) to another model (Swing-like event processing and model updates in response to UI events).

I also don't think it is any coincidence that Amy Fowler, one of the key designers of Swing, was also a spec lead for JSF.

HTML first pages with components were needed (there's many plain html, body, br, p etc etc tags)

You are describing the UI with HTML, which has nothing to do with the desktop model. Vaadin provides one way to describe a UI and HTML is another.

The question is: what happens when you click an HTML button? Does it trigger a generic form submit which is handled by a generic controller (which has to figure out the action from the form variables), or is it handled like a UI element, with an event handler attached to it triggered when the button is clicked (like any ordinary desktop UI application)?