How to validate availability of username in database?

Question

How can I validate the entered username in an input text field if it is available according to the database? I am using JSF2.

Answer 1

Just implement a Validator yourself.

@ManagedBean
@RequestScoped
public class UserNameAvailableValidator implements Validator {

    @EJB
    private UserService userService;

    @Override
    public void validate(FacesContext context, UIComponent component, Object value) throws ValidatorException {
        String userName = (String) value;

        if (!userService.isUsernameAvailable(userName)) {
            throw new ValidatorException(new FacesMessage("Username not avaliable"));
        }
    }

}

(please note that it's a @ManagedBean instead of @FacesValidator because of the need to inject an @EJB; if you're not using EJBs, you can make it a @FacesValidator instead)

Use it as follows:

<h:inputText id="username" value="#{register.user.name}" required="true">
    <f:validator binding="#{userNameAvailableValidator}" />
    <f:ajax event="blur" render="username_message" />
</h:inputText>
<h:message id="username_message" for="username" />