How to parameterize requiredMessage attribute in composite component?

Question

BalusC provided a good answer to a question about how to set messages per composite component. Specifying different error messages for different composite components The ans

Answer 1

Unfortunately, the requiredMessage (and validatorMessage and converterMessage) attribues are not parameterizable by default. I think it would make little sense anyway as they are tied to a specific component in particular. A composite component does usually not contain a multiple of the same components. You would need to specify separate messages for every individual component.

It's in theory however possible to create a custom EL function which does the message formatting job. The method would look something like this:

public static String format(String message, Object argument1, Object argument2) {
    return MessageFormat.format(message, argument1, argument2);
}

which is to be used something like this:

requiredMessage="#{util:format(cc.resourceBundleMap.requiredMessage, cc.attrs.prefix, cc.attrs.label)}"

The only disadvantage is that you can't create EL functions which can take varargs. This is a limitation of the EL specification. So if you intend to be able to pass variable arguments, you'd need to create a separate EL function and a Java method for every possible amount of arguments needed.

As a completely different alternative, you could create a custom Validator and attach it to the particular input component. You can even put the validator method straight in the "backing component" which is associated with the composite component by . If you remove the required attribute, then this validator will immediately be invoked where you've the freedom to compose messages the way you want.

E.g.

with

public void validateFoo(FacesContext context, UIComponent component, Object value) {
    if (value == null || value.toString().trim().isEmpty()) {
        String requiredMessage = (String) component.getAttributes().get("requiredMessage");
        String prefix = (String) getAttributes().get("prefix");
        String label = (String) getAttributes().get("label");
        throw new ValidatorException(new FacesMessage(FacesMessage.SEVERITY_ERROR,
            MessageFormat.format(requiredMessage, prefix, label), null));
    }
}