Implement callback method in JSF composite component - jsf-2.2

Question

I'd like to implement a "callback" feature in my composite component. This method would be called from the 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 the exp gets null value. How can I get the callback attribute, and how can I execute it?

Answer 1

A solution (Java 1.8) to call a function with no args.
Component:
<composite:interface>
<composite:attribute name="buttonCallback" type="java.util.function.Consumer"/>
</composite:interface>
<composite:implementation>
<p:commandButton value="Submit" action="#{cc.attrs.buttonCallback.accept(null)}"/>
<composite:implementation>
Usage in view:
<mycomp:myCC buttonCallback="#{myBackingBean.myCallback}"/>
Usage in backing bean:
private Consumer<Void> myCallback;
#PostConstruct
public void init() {
myCallback= this::myFunction;
}
public void myFunction(Void v) { //... }