FacesContext.addMessage(String, FacesMessage) requires the component's clientId, not it's id. If you're wondering why, think about having a control as a child of a dataTable, stamping out different values with the same control for each row - it would be possible to have a different message printed for each row. The id is always the same; the clientId is unique per row.
So "myform:mybutton" is the correct value, but hard-coding this is ill-advised. A lookup would create less coupling between the view and the business logic and would be an approach that works in more restrictive environments like portlets.
<f:view>
<h:form>
<h:commandButton id="mybutton" value="click"
binding="#{showMessageAction.mybutton}"
action="#{showMessageAction.validatePassword}" />
<h:message for="mybutton" />
</h:form>
</f:view>
Managed bean logic:
/** Must be request scope for binding */
public class ShowMessageAction {
private UIComponent mybutton;
private boolean isOK = false;
public String validatePassword() {
if (isOK) {
return "ok";
}
else {
// invalid
FacesMessage message = new FacesMessage("Invalid password length");
FacesContext context = FacesContext.getCurrentInstance();
context.addMessage(mybutton.getClientId(context), message);
}
return null;
}
public void setMybutton(UIComponent mybutton) {
this.mybutton = mybutton;
}
public UIComponent getMybutton() {
return mybutton;
}
}