In this article I will show you how you can embed an existing Liferay portlet into your own plug-in portlet without using Ext. This might be useful in several scenarios, for example: building your own ‘nested portlet’ portlet or include the web form portlet in your own portlet.

The solutions works in Liferay 6.0 EE SP1 and can include portlets from Liferay itself as well as portlets coming from other plug-ins. Other versions of Liferay have not been tested yet.

I hope this snippet is as useful to you as it is to me!

package nl.liones.liferay;
import com.liferay.portal.kernel.exception.SystemException;
import com.liferay.portal.kernel.portlet.PortletBag;
import com.liferay.portal.kernel.portlet.PortletBagPool;
import com.liferay.portal.kernel.util.WebKeys;
import com.liferay.portal.service.PortletLocalServiceUtil;
import com.liferay.portal.theme.PortletDisplay;
import com.liferay.portal.theme.ThemeDisplay;
import com.liferay.portal.util.PortalUtil;
import com.liferay.portal.util.PortletKeys;
import javax.portlet.PortletRequest;
import javax.portlet.PortletResponse;
import javax.portlet.ValidatorException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
/**
 * Portlet embed utility method.
 *
 * @author Stef Busking (Liones), Bert Willems (Liones)
 */
public class RuntimePortletEmbedUtil {
    /**
     * Renders the given portlet as a runtime portlet and returns the portlet's HTML.
     *
     * @param request     The {@link PortletRequest}.
     * @param response    The {@link PortletResponse}.
     * @param portletId   The ID of the portlet to render, includes instance ID for instance portlets.
     * @param queryString The query string to use for the portlet.
     * @return The HTML for the given portlet.
     * @throws SystemException    on error.
     * @throws IOException        on error.
     * @throws ServletException   on error.
     * @throws ValidatorException on error.
     */
    public static String renderPortlet(final PortletRequest request, final PortletResponse response, final String portletId, final String queryString) throws SystemException, IOException, ServletException, ValidatorException {
        // Get servlet request / response
        HttpServletRequest servletRequest = PortalUtil.getOriginalServletRequest(PortalUtil.getHttpServletRequest(request));
        HttpServletResponse servletResponse = PortalUtil.getHttpServletResponse(response);
        // Get theme display
        final ThemeDisplay themeDisplay = (ThemeDisplay) servletRequest.getAttribute(WebKeys.THEME_DISPLAY);
        // Backup current state
        PortletDisplay portletDisplay = themeDisplay.getPortletDisplay();
        PortletDisplay portletDisplayClone = new PortletDisplay();
        portletDisplay.copyTo(portletDisplayClone);
        final Map<String, Object> requestAttributeBackup = new HashMap<String, Object>();
        for (final String key : Collections.list((Enumeration<String>) servletRequest.getAttributeNames())) {
            requestAttributeBackup.put(key, servletRequest.getAttribute(key));
        }
        // Render the portlet as a runtime portlet
        String result;
        try {
            PortletBag implPortletBag = PortletBagPool.get(PortletKeys.JOURNAL);
            com.liferay.portal.model.Portlet portlet = PortletLocalServiceUtil.getPortletById(PortalUtil.getCompanyId(request), portletId);
            servletRequest.setAttribute(WebKeys.RENDER_PORTLET_RESOURCE, Boolean.TRUE);
            result = PortalUtil.renderPortlet(implPortletBag.getServletContext(), servletRequest, servletResponse, portlet, queryString, false);
        } finally {
            // Restore the state
            portletDisplay.copyFrom(portletDisplayClone);
            portletDisplayClone.recycle();
            for (final String key : Collections.list((Enumeration<String>) servletRequest.getAttributeNames())) {
                if (!requestAttributeBackup.containsKey(key)) {
                    servletRequest.removeAttribute(key);
                }
            }
            for (final Map.Entry<String, Object> entry : requestAttributeBackup.entrySet()) {
                servletRequest.setAttribute(entry.getKey(), entry.getValue());
            }
        }
        return result;
    }
}

Using this code
The snippet below demos how to embed the Liferay Web Form portlet and how to set a preference for this embedded portlet.

final String portletId = "1_WAR_webformportlet_INSTANCE_abcd";
final ThemeDisplay themeDisplay = (ThemeDisplay) request.getAttribute(WebKeys.THEME_DISPLAY);
// get the preferences
final PortletPreferences prefs = PortletPreferencesUtilityLocalServiceUtil.getWrappedPortletPreferences(themeDisplay, portletId);
// set a preference
prefs.setValue("successURL", "some url");
// dont forget to store the preferences
formPrefs.store();
// get the HTML from the portlet
final String portletHtml = RuntimePortletEmbedUtil.renderPortlet(request, response, portletId, "");