gistfile1.jsp

<portlet:renderURL var="myResourceURL">
    <portlet:param name="mvcPath" value="/my_file.jsp" />
    <portlet:param name="redirect" value="<%= currentURL %>" />
    <portlet:param name="myCustomParam" value="{myCustomParam}" />
</portlet:renderURL>

var resourceURL = A.Lang.sub(
    decodeURIComponent('<%= myResourceURL %>'),
    {
        myCustomParam: myCustomParam
    }
);

A.io(resourceURL, {
    on: {
        complete: function() {}
    }
});