Validate input as required only if certain command button is pressed

Question

I have specific use case for JSF validation. For example I have an inputText field:

Answer 1

Just remove the required attribute as you accept the input if the input is empty. Then write a custom validator which accepts only empty input or numerical input.

public class customerNumericInputValidator implements Validator {

@Override
public void validate(FacesContext facesContext, UIComponent uIComponent,
        Object object) throws ValidatorException {

    String number = (String) object;
    number = Strings.nullToEmpty(number).trim();

    //if the request is a full request then number can not be empty
    if(!FacesContext.getCurrentInstance().isPostback() && Strings.isNullOrEmpty(number))
    {
         FacesMessage message = new FacesMessage();
         message.setSummary(Messages.getMessage("error empty value"));
         message.setSeverity(FacesMessage.SEVERITY_ERROR);
         throw new ValidatorException(message);
    } 

    if(!Strings.isNullOrEmpty(number))
    { 
        if(!isNumber(number))
        {
           FacesMessage message = new FacesMessage();
           message.setSummary(Messages.getMessage("error not numerical value"));
           message.setSeverity(FacesMessage.SEVERITY_ERROR);
           throw new ValidatorException(message);
        }
    }
}

}