If the input of one of the components on your page is validated by a backing bean method, you refer to the method from the component’s tag using the validator attribute.
The Coffee Break application includes a method that performs validation of the email input component on the checkoutForm.jsp page. Here is the tag corresponding to this component:
<h:inputText id="email" value="#{checkoutFormBean.email}" size="25" maxlength="125" validator="#{checkoutFormBean.validateEmail}"/>
This tag references the validate method described in Writing a Method to Perform Validation using a method expression.