Getting response form custom @proceesAction in WebSphere Portal Portlet

I am developing a Portlet in WebSphere Portal 8 and I am having problems getting the response from a custom @processAction method, the method is called and executed, but in the jsp I can't get the data returned.

I have a jsp file which has:

-definition of portlet actionURL...

<portlet:defineObjects/>
<portlet:actionURL var="cargarListadoConcursosURL">
       <portlet:param name="<%=ActionRequest.ACTION_NAME%>" value="cargarListadoConcursos" />
    </portlet:actionURL>

-JavaScript method with ajax post method:

<script type="text/javascript">
    $(document).ready(function() {
        cargarListadoConcursos();
    });
    
    function cargarListadoConcursos() {
        $.ajax({
            url : '<%=cargarListadoConcursosURL%>',
            type : 'POST',
            dataType : 'json',
            success : function(data) {
                alert(data);
                //do something!!!
            }
        });
    }

and my portlet class looks like:

public class ListadoConcursosPortlet extends GenericPortlet
{
   //more methods...

    @ProcessAction(name="cargarListadoConcursos")
    public void cargarListadoConcursos(ActionRequest request, ActionResponse response) throws PortletException, IOException {
        HttpServletResponse resp = PortletUtils.getHttpServletResponse(response);
        resp.setContentType("application/json");
        resp.setCharacterEncoding("UTF-8");
        PrintWriter writer = resp.getWriter();
        writer.append(gson.toJson(new ArrayList<Concurso>()));
        writer.flush();
        resp.flushBuffer();
        System.out.println("Paso por cargarListadoConcursos");
    }
}

I think that the portlet.xml its fine because the jsp call the portlet controller (the syso appears at console)...

Well in conclusion, the problems is that I can't get the JSON object in my JavaScript called, and the alert(data) is never executed...

The issue is that the page is refreshed when you it the actionURL. You need to use a Resource Serving Portlet, the serveResource method and an resourceURL which doesn't refresh the page when called.