Java EE (Java Enterprise Edition) General Discussion

hi, how to trigger onerror of f:ajax inside a h:commandButton from it's action method?

<h:form>
   <h:inputText id="i1" value="#{bean.i1}"/>
   <h:commandButton id="go" action="#{bean.process}" value="go">
      <f:ajax render="o1" onerror="myfunction();"/>
   </h:commandButton>
   <h:outputText id="o1" value="#{bean.o1}"/>
</h:form>

then in the bean

    public String process() {
        if(isOK()) {
            calculate();
            return null;
        } else {
            //here I want to send an ajax error, to trigger the onerror function in the client
        }
   }

I don't know what I must do inside the action method to signalize an ajax error. Do I have to throw a specific Exception or any run time exception, or another approach?