The theme-uri-handler-class Element
It specifies the class to provide the theme (aka., a style sheet file) URI dynamically if you want to determine the theme based on the current user, cookie or locale. You can implement a class with the ThemeURIHandler interface, and specify it with the
theme-uri-handler-class element. Then, an instance of the class will be created. It will be called each time when a desktop is rendered to the client to determine the theme URI before ThemeProvider.
Different from ThemeProvider, ThemeURIHandler is composable with other ThemeURIHandler.
Note: ThemeProvider still has the final decision. ThemeURIHandler will always be executed.