ZK portlet loader is a generic loader. To load a particular ZUML page, you have to specify either a request parameter, a portlet attribute or a portlet preference called zk_page, if you want to load a ZUML page, or zk_richlet, if you want to load a richlet.
More precisely, ZK portlet loader first checks the following locations for the path of the ZUML page or the richlet. The lower the number, the higher the priority.
The request parameter (RenderRequest's getParameter) called zk_page. If found, it is the path of the ZUML page.
The request attribute (RenderRequest's getAttribute) called zk_page. If found, it is the path of the ZUML page.
The request preference (RenderRequest's getPortletPreferences's getValue) called zk_page. If found, it is the path of the ZUML page.
The request parameter (RenderRequest's getParameter) called zk_richlet. If found, it is the path of the richlet.
The request attribute (RenderRequest's getAttribute) called zk_richlet. If found, it is the path of the richlet.
The request preference (RenderRequest's getPortletPreferences's getValue) called zk_richlet. If found, it is the path of the richlet.
The initial parameter (PortletConfig's getInitParameter) called zk_page. If found, it is the path of the ZUML page.