jsf 2.2 - Implement callback method in JSF composite component -

i'd implement "callback" feature in composite component. method called backing component when necessary.

the xhtml part is:

    <cc:interface componenttype="partnerselcomp">         <cc:attribute name="value" type="com.app.data.partner"/>                     <cc:attribute name="callback" method-signature="void notify(java.lang.long)"/>                 </cc:interface>      <cc:implementation>         <span id="#{cc.clientid}">                                             <p:inputtext id="code" binding="#{cc.partnercode}">                                      <p:ajax event="blur" update="code name msg" listener="#{cc.validate}" />                                                                                                                 </p:inputtext>              <p:outputlabel id ="name" binding="#{cc.partnername}"/>                                                          <p:message id="msg" for="code"/>                         </span>     </cc:implementation> 

the relevant part of backing component is:

@facescomponent("partnerselcomp") public class partnerselcomp extends uiinput implements namingcontainer {      private inputtext partnercode;         private outputlabel partnername;              @override     public string getfamily() {         return uinamingcontainer.component_family;     }      public void validate() {         ...         methodexpression exp = (methodexpression) getattributes().get("callback");          ...                }     ...                     } 

above exp gets null value. please how can "callback" attribute, , how can execute it?