您需要的是Validator.它应该看起来像这样:

What you need is a Validator. It should look like this:

@ManagedBean
@RequestScoped
public class DiscountCodeValidator implements Validator {
    @EJB
    private MrBean mrBean;

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

        if (!mrBean.checkDiscountCodeExistence(discountCode)) {
            throw new ValidatorException(new FacesMessage("This code is not valid!"));
        }
    }
}

在您的.xhtml文件中，您可以按以下方式声明此验证器:

In your .xhtml file, you can declare this validator as following:

<h:inputText id="discountCode" value="#{someBean.discountCode}" 
             validator="#{discountCodeValidator}" 
             required="true" requiredMessage="Discount code is required.">
   <f:ajax event="blur" render="discountMsg" />
</h:inputText>
<h:message for="discountCode" id="discountMsg"/>

要注意的一件事是，我假设您将注入一个EJB以使用checkDiscountCodeExistence()函数检查折扣代码的存在.因此，我将上述验证器注释为@ManagedBean.如果不需要注入任何EJB，则可以使用@FacesValidator注释验证器.

One thing to note is I assume that you would inject an EJB to check the existence of the discount code with the checkDiscountCodeExistence() function. Hence, I annotated the above Validator as a @ManagedBean. If you don't need to inject any EJBs, you can annotate the Validator with @FacesValidator.