JSF FacesContext#addMessage is not displayed - jsf

Question

In my previous question I had the problem of displaying validation messages from a Login form. That issue is now solved, but this time I am not able to display a custom message with FacesContex#addMessage.
Using JSF + PrimeFaces.
<p:dialog header="Login" widgetVar="loginDlg">
<h:form id="loginForm">
<h:panelGrid columns="3" cellpadding="5">
<h:outputLabel for="username" value="Username:" />
<p:inputText value="#{loginBean.username}" id="username" required="true" label="username" />
<p:message for="username" />
<h:outputLabel for="password" value="Password:" />
<h:inputSecret value="#{loginBean.password}" id="password" required="true" label="password" />
<p:message for="password" />
<f:facet name="footer">
<p:commandButton value="Login" id="loginDlgButton" update=":loginForm,:welcomeMsg" actionListener="#{loginBean.login}"
oncomplete="handleLoginRequest(xhr, status, args)"/>
<p:message for="loginDlgButton" />
</f:facet>
</h:panelGrid>
</h:form>
</p:dialog>
In LoginBean (a SessionScoped ManagedBean):
public void login() {
FacesContext context = FacesContext.getCurrentInstance();
RequestContext rContext = RequestContext.getCurrentInstance();
HttpServletRequest request = (HttpServletRequest) context.getExternalContext().getRequest();
try {
request.login(this.username, this.password);
rContext.addCallbackParam("loggedIn", true);
} catch (ServletException e) {
rContext.addCallbackParam("loggedIn", false);
context.addMessage(null, new FacesMessage(FacesMessage.SEVERITY_WARN, "Login Error", "Invalid credentials"));
}
}
This code, when validation succeeds and login fails, should display the "Invalid credential" message, but doesn't. Moreover, somewhere in the body of my web page, I have also added this line:
<p:messages autoUpdate="true" />
but my message isn't displayed even there.
Javadocs say that
If clientId is null, this FacesMessage is assumed to not be associated with any specific component instance
But I can't understand what this means.

Answer 1

place <p:messages autoUpdate="true" /> inside your form or inside some wrapper that is being updated by update of your commandButton , or place loginDlgButton instead of null in context.addMessage(...

Answer 2

I don't see a p:messages tag in your code. It is not the same as the p:message tag. p:message is attached to another component and is displayed as part of validation. The p:messages (or p:growl) component is what you are updating in your bean. Try adding a messages or growl component like this:
<h:form id="loginForm">
<p:growl id="messageGrowl" showDetail="true" sticky="false" />
<h:panelGrid columns="3" cellpadding="5">