Showing error or success message on same page - html

Question

this is my first time posting here since I couldn't figure the issue out, please keep in mind im fairly new to Spring and not that good at Java and coding in general.
I'm trying to program a Server application with Java Spring where you're able to create different accounts with specific roles. I want my users to be able to see a success or error message on the same page if the creation of an account succeded or failed.
Right now I'm using the error.param th:if tag from https://spring.io/guides/gs/securing-web/
the specific code in my HTML file is:
<div id="error" th:if="${param.error}">
Benutzername existiert bereits.
</div>
<div id="success" th:if="${param.success}">
Das Konto wurde erfolgreich erstellt.
</div>
Which works when I manually put ?success or ?error behind my URL.
I map my POST to the database by this method:
#PostMapping("/create/lieferant/fahrer")
public String submitDriver(#ModelAttribute Driver driver){
if(userRepository.existsByUsername(driver.getUsername())){
return "create/lieferant/fahrer?error";
}
Driver d = new Driver();
User n = new User();
Role r = new Role();
d.setName(driver.getName());
d.setTelnum(driver.getTelnum());
d.setUsername(driver.getUsername());
n.setUsername(driver.getUsername());
n.setPassword(encoder().encode(driver.getPassword()));
r.setUsername(driver.getUsername());
r.setAuthority("LIEFERANT");
userRepository.save(n);
driverRepository.save(d);
roleRepository.save(r);
return "create/lieferant/fahrer?success";
}
The idea is to check if the username is already registered and if so, returning the create/lieferant/fahrer?error but it says
Error resolving template "create/lieferant/fahrer?error", template
might not exist or might not be accessible by any of the configured
Template Resolvers
and the same for ?success.
What I don't understand is: it's working for the login which I've gotten from the Spring getting started guide and it seems to be working without any heavy configurations or so. Atleast I don't see any.
I'd be glad if anyone could help me figuring my issue out.
Thanks a lot.

Answer 1

You could do something like this:
#PostMapping("/create/lieferant/fahrer")
public ModelAndView submitDriver(#ModelAttribute Driver driver){
ModelAndView mav = new ModelAndView();
mav.setViewName("create/lieferant/fahrer");
try {
if(userRepository.existsByUsername(driver.getUsername())){
return "create/lieferant/fahrer?error";
}
Driver d = new Driver();
User n = new User();
Role r = new Role();
d.setName(driver.getName());
d.setTelnum(driver.getTelnum());
d.setUsername(driver.getUsername());
n.setUsername(driver.getUsername());
n.setPassword(encoder().encode(driver.getPassword()));
r.setUsername(driver.getUsername());
r.setAuthority("LIEFERANT");
userRepository.save(n);
driverRepository.save(d);
roleRepository.save(r);
mav.addObject("success", "All was ok");
} catch (Exception e) {
mav.addObject("error", "Error message to change");
}
return "create/lieferant/fahrer?success";
}
You could retrieve messages on page with the two keys "success" and "error"