@NonNull annotation allows null values in validation

MrD :

I have the following method in my controller:

@PostMapping("/register")
    public String registerNewUser(@Valid User user, BindingResult result, Model model, RedirectAttributes redirectAttributes) {
        System.out.println(result);
        System.out.println(user);
        if(result.hasErrors()) {
            System.out.println("***ERROR***");
            System.out.println(result.getAllErrors());
            return result.getAllErrors().toString();
        } else {
            //userRepository.save(user);
            System.out.println("user saved!");
            return "user saved!";
        }
    }

And my user entity specifies:

@NonNull
@Column(nullable = false, unique = true)
@Valid
public String alias;

Now if I make a simple post request (I use the Advanced REST client for chrome extension) I get:

org.springframework.validation.BeanPropertyBindingResult: 0 errors
User(id=null, email=null, password=null, enabled=false, firstName=null, lastName=null, fullName=null null, alias=null, roles=[], links=[])
user saved!

Where it seems to validate despite @NonNull alias being null.

If I change @NonNull to @NotEmpty

Then validation works as expected:

[Field error in object 'user' on field 'alias': rejected value [null]; codes [NotEmpty.user.alias,NotEmpty.alias,NotEmpty.java.lang.String,NotEmpty]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [user.alias,alias]; arguments []; default message [alias]]; default message [must not be empty]]

BUT what I don't understand is why @NonNull allows Nulls?

Andronicus :

You should use NotNull from javax.validation package and not from lombok (those are to be deleted, when java starts supporting validation - see here). It validates the beans. More info here. You can also use hibernate's @NotNull from org.hibernate.validator. This also does validation.