redirect doesn't work in the Spring controller

Hhere is a registration field, after registration it should go to the menu page, but it goes to main

@Controller
@RequestMapping("/main")
public class SignInPageController {

    private UserDao userDao;
@Autowired
    public SignInPageController(UserDao userDao){this.userDao = userDao;}

@GetMapping("/menu")
    public String mainMenuPage(){
        return "main/menu";
    }
@GetMapping("/signup")
    public String signUpPage(Model model){
        model.addAttribute("newuser", new User());
        return "main/signup";
    }
@PostMapping("/signup")
    public String signUp(@RequestParam("name") String name,
                             @RequestParam("password") String password,
                             @RequestParam("email") String email,
                             @RequestParam("nativeLanguage") String nativeLanguage){
        User user = new User(name, password, email, nativeLanguage);
        userDao.signUpUser(user);
        return "redirect:/main/menu";
    }

can you tell me what the problem is?

It looks like you are missing the @Controller Spring annotation on your SignInPageController class.

So you should get something like this:

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
// And your other imports...

@Controller
@RequestMapping("/main")
public class SignInPageController {

    private UserDao userDao;

    @Autowired
    public SignInPageController(UserDao userDao){this.userDao = userDao;}

    @GetMapping("/menu")
    public String mainMenuPage(){
        return "main/menu";
    }

    @GetMapping("/signup")
    public String signUpPage(Model model){
        model.addAttribute("newuser", new User());
        return "main/signup";
    }

    @PostMapping("/signup")
    public String signUp(@RequestParam("name") String name,
                             @RequestParam("password") String password,
                             @RequestParam("email") String email,
                             @RequestParam("nativeLanguage") String nativeLanguage){
        User user = new User(name, password, email, nativeLanguage);
        userDao.signUpUser(user);
        return "redirect:/main/menu";
    }
}

So as I was saying in the comments :

You should be returning a ModelAndView type from your controller's method, with a return such as :

return new ModelAndView("redirect:/main/menu", model);

As you mentionned you also encoutered an issue with a incorrect redirection, try to use defined CONSTANTS to avoid typos

If you're new to Spring, make sure to look into RedirectAttributes, adding flashAttributes, and check the documentation on Baeldung it is really complete.

Good luck !