[Java Spring] Validations for Entity

import javax.validation.constraints.*;
@Entity
public class User {
    @Id
    private int id;

    @Size(min = 6, message = "Username cannot be less than 6 characters")
    private String username,

    @Pattern(regexp = "((?=.[A-Z]).{6,10})", message = "Password must have one upperCase, one lower case....")
    private String password;

    @NotNull(message = "Activity cannot be left empty")
    private String activity;

    @NotEmpty(message="First name cannot be empty")
    private String firstName;

    ....

}

@PostMapping("/registeruser")
public String registerUser(@Valid @ModelAttribute("newuser") User user, BindingResult result, Model model) {

   // BindingResult will show the error message is Validation failed.
    
    if (result.hasErrors()) {
        return "register"
    }

       ...
}