how to validate params in form action method

[meatseam]

Hi to everyone.
I'm trying to use Hibernate Validator (es. @Length, @NotNull, @Pattern, ..)
for form params.
If I use a Seam-style param passing, i.e. putting the params in the form action method call, the seam bean isn't able to validate the params values.

I can't use the above annotations on the method sign.

This is my situation:

<h:form id="form">
     <h:inputText id="formParam" binding="#{requestScope.formParam}"
      required="true" requiredMessage="Missing Form Param!" />

     <h:commandButton action="#{seamBean.doStuff(requestScope.formParam.value)}"
      value="Do Stuff" type="submit" />
</h:form>

@Length(min = 16, max = 16, message = "...")
@NotEmpty(message = "....!")
@NotNull(message = "...")
@Pattern(regex = "....", message = ".....")
public String printByCodiceFiscale(String formParam) {
     .....
}

Using a JSF-style, i.e. the form params become seam bean's properties, it works because I move the annotations on top of the declared java class properties.

Thank you in advance