@ModelAttribute for complex objects

Question

I have a user entity that has many attributes (some fields not shown here):

@Entity
public class User {

    @OneToOne(cascade = ALL, orphanRemoval = true)
    private File avatar; // File is a custom class I have created

    @NotEmpty
    @NaturalId
    private String name;

    @Size(min = 6)
    private String password;

    @Enumerated(EnumType.STRING)
    private Role role;
}

In my thymeleaf template I have a form that submits username, password and avatar (MultipartFile). Now in my controller instead of these parameters...

@PostMapping("/register")
public String register(@RequestParam String username,
                       @RequestParam String password,
                       @RequestParam MultipartFile avatar) { ...

...I want to use @ModelAttribute @Valid User user. My problem is that:

1. password first should be encrypted then passed to the user entity,
2. bytes[] from MultipartFile should be extracted then stored in user entity (as a custom File object),
3. some other fields such as Role should be set manually in the service class.

How can I take advantage of @ModelAttribute?

Answer 1

Instead of trying to shoehorn everything into your User class, write a UserDto or UserForm which you can convert from/to a User. The UserForm would be specialized for the web and converted to a User later on.

The conversions you are talking about should be done in your controller (as that is ideally only a conversion layer before actually talking to your business services).

public class UserForm {

    private MultipartFile avatar; 

    @NotEmpty
    private String username;

    @Size(min = 6)
    @NotEmpty
    private String password;

    public UserForm() {}

    public UserForm(String username) {
         this.username = username;
    }

    static UserForm of(User user) {
        return new UserForm(user.getUsername());
    }

    // getters/setters omitted for brevity
}

Then in your controller do what you intended to do (something like this):

@PostMapping("/register")
public String register(@ModelAttribute("user") UserForm userForm, BindingResult bindingResult) {
    if (!bindingResult.hasErrors()) {
      User user = new User();
      user.setName(userForm.getUsername());
      user.setPassword(encrypt(userForm.getPassword());
      user.setAvataor(createFile(userForm.getAvatar());
      userService.register(user);
      return "success";
    } else {
      return "register";
    }
} 

This way you have a specialized object to fix your web based use cases, whilst keeping your actual User object clean.