I had this same issue after a Windows update restarted my machine with Eclipse still running. When I restarted Eclipse, it was complaining about not being able to find java.sql.Connection.

No amoount of Maven dancing (Alt-F5, Select All, Refresh), starting Eclipse -clean or other jiggery pokery did anything, until I went into Window, Preferences, Java, Compiler, and I selected a Compliance Level other than the one listed (and supported for my JDK) and clicked Apply And Close.

This warns about a rebuild, but it was the rebuild that fixed the issue