Type Mismatch cannot convert from type Optional<User> to User

Question

I am trying to create a website that allows the user to update, edit, delete, etc., and I have got to the part of Updating or Editing user’s information. I have tried multiple times using different ways, but I cannot seem to get past the error. I am completely oblivious to Optional<> I just don’t get it. I have read https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html, but i dont understand how it should be coded, its just not clicking. If someone could please inform on how it should be coded in my code and please explain it I would be so grateful. Maybe its because im overworked and have not slept, but i cannot seem to correct this error. This is the error i get on the page when i attempt to edit the information for a user:

There was an unexpected error (type=Internal Server Error, status=500). For input string: "id" java.lang.NumberFormatException: For input string: id

    //Repository

    public interface UserRepository extends CrudRepository<User, Integer> {
     }

here is the UserService

    //UserService

    @Service
    @Transactional
    public class UserService {

        private final UserRepository userRepository;

        public UserService(UserRepository userRepository) {
            this.userRepository=userRepository;

        }
        public void saveMyUser(User user) {
            userRepository.save(user);
        }

        public List<User> showAllUsers(){

            List<User> users = new ArrayList<User>();
            for(User user: userRepository.findAll()) {
                users.add(user);
            }

            return users;
        }

        public void deleteMyUser(int id) {
            userRepository.deleteById(id);

        }

        public User editUser (int id) {

            return userRepository.findById(id);//I also get an error here as well
        }

    }

here is the controller

    //Application Controller

    @Controller
    public class ApplicationController {

        @Autowired
        private UserService userService;

        // THIS IS WHERE I GET THE ERROR

        @RequestMapping("/edit-user")
        public String editUser(@RequestParam int id,HttpServletRequest request) {

            /* OPTIONAL<?> is this where i would implement the 
               optional what do i have to put here exactly? 
               I tried some ways I read about but its not working for me */

            request.setAttribute("user", userService.editUser(id));
            request.setAttribute("mode", "MODE_UPDATE");
            return "welcome";
        }

    }

Thank you for the help in advance Im a little frustrated with this because I have been trying to correct this error all night.

Answer 1

There are several ways to convert from an option to an entity. You can use the following:

Use get() method:

 public User editUser (int id) {
      return userRepository.findById(id).get();
 }

Use orElse method:

public User editUser (int id) {
    /* new User() is stab if user was not found */
    return userRepository.findById(id).orElse(new User());
}

Use orElseThrowMethod:

public User editUser (int id) {
        /* Throw exception if user was not found*/
        return userRepository.findById(id).orElseThrow(IllegalArgumentException::new));
    }

As for controller it will be like this:

        @RequestMapping("/edit-user")
        public String editUser(@RequestParam int id,HttpServletRequest request) {

            User user = userService.editUser(id);

            request.setAttribute("user", user);
            request.setAttribute("mode", "MODE_UPDATE");
            return "welcome";
        }

Also there similar question for your topic:

Spring Boot. how to Pass Optional<> to an Entity Class