Bean validation

public class UserProfile {

    @NotNull(message = "Login must be not null.")
    @Size(min = 3, message = "Login must contain at least three characters.")
    private String login;

    @NotNull(message = "Password must be not null.")
    @Size(min = 5, message = "Password must contain at least five characters.")
    private String password;

    @NotNull(message = "Email must be not null.")
    @Email(message = "Email is invalid.")
    private String email;

    // getters and setters
}

class UserProfile(

    @NotNull(message = "Login must be not null.")
    @Size(min = 3, message = "Login must contain at least three characters.")
    var login: String,

    @NotNull(message = "Password must be not null.")
    @Size(min = 5, message = "Password must contain at least five characters.")
    var password: String,

    @NotNull(message = "Email must be not null.")
    @Email(message = "Email is invalid.")
    var email: String
)

@RestController
{1}
public class UserProfileController {

    @GetMapping("/users/{login}")
    ResponseEntity<String> getUserByLogin(
            @PathVariable("login") {2} String login) {
        return ResponseEntity.ok("User id is valid.");
    }

    @PostMapping("/users")
    public ResponseEntity<String> addNewUserProfile(@RequestBody {3} {4} user) {
        return ResponseEntity.ok("User info is valid.");
    }
}

@RestController
{1}
class UserProfileController {

    @GetMapping("/users/{login}")
    fun getUserByLogin(@PathVariable("login") {2} login: String): ResponseEntity<String>  {
        return ResponseEntity.ok("User id is valid.")
    }

    @PostMapping("/users")
    fun addNewUserProfile(@RequestBody {3} user: {4}): ResponseEntity<String> {
        return ResponseEntity.ok("User info is valid.")
    }
}