To use it, you first have to add the following definition into WEB-INF/portlet.xml. Notice that expiration-cache must be set to zero to prevent portals from caching the result.

<portlet>
    <description>ZK loader for ZUML pages</description>    
    <portlet-name>zkPortletLoader</portlet-name>    
    <display-name>ZK Portlet Loader</display-name>    

    <portlet-class>org.zkoss.zk.ui.http.DHtmlLayoutPortlet</portlet-class>    

    <expiration-cache>0</expiration-cache>    

    <supports>    
        <mime-type>text/html</mime-type>        
        <portlet-mode>VIEW</portlet-mode>        
    </supports>    

    <supported-locale>en</supported-locale>    

    <portlet-info>    
        <title>ZK</title>        
        <short-title>ZK</short-title>        
        <keywords>ZK,ZUML</keywords>        
    </portlet-info>    
</portlet>