import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
@Controller
public class IndexController
{
    @GetMapping("/")
    public String index() {
        //int i = 9/0;   error page test
        return "index";
    }
}
There is a wave line under the "index". And IDEA tells me that it cannot resolve MVC View 'index'. I have already put index page and error page under the templates directory, when I run it and it still shows me a whitelable error page. Surprisingly, it works(open a index page) when i use @RestController instead of @Controller, but still show me whitelabel error page when I want to open a 404 page and 500 page.
 
     
    