Passing Information from the Action Phase to the Render Phase

There are two ways to pass information from the action phase to the render phase. The first way is through render parameters. In the processAction method you can invoke the setRenderParameter method to add a new parameter to the request. The render phase can read this:

actionResponse.setRenderParameter("parameter-name", "value");

From the render phase (in our case, the JSP), this value is read like this:

renderRequest.getParameter("parameter-name");

It’s important to be aware that when invoking an action URL, the parameters specified in the URL are only readable from the action phase (that is within the processAction method). In order to pass parameter values to the render phase you must read them from the actionRequest and then invoke the setRenderParameter method for each parameter needed.

Tip: Liferay offers a convenient extension to the portlet specification through the MVCPortlet class to copy all action parameters directly as render parameters. You can achieve this by setting the following init-param in your portlet.xml:

<init-param>
    <name>copy-request-parameters</name>
    <value>true</value>
</init-param>

One final note about render parameters: the portal remembers them for all later executions of the portlet until the portlet is invoked with different parameters. That is, if a user clicks a link in our portlet and a render parameter is set, and then the user continues browsing through other portlets on the page, each time the page is reloaded, the portal renders our portlet using the render parameters that we initially set. If we used render parameters in our example, then the success message will be shown not only right after saving, but also every time the portlet is rendered until the portlet is invoked again without that render parameter.

The second way of passing information from the action phase to the render phase is not unique to portlets, so it might be familiar to you–using the session. Your code can set an attribute in the actionRequest that is then read from the JSP. In our case, the JSP would also immediately remove the attribute from the session so the message is only shown once. Liferay provides a helper class and taglib to do this operation easily. In the processAction method, you need to use the SessionMessages class:

package com.liferay.samples;

import java.io.IOException;
import javax.portlet.ActionRequest;
import javax.portlet.ActionResponse;
import javax.portlet.PortletException;
import javax.portlet.PortletPreferences;
import com.liferay.portal.kernel.servlet.SessionMessages;
import com.liferay.util.bridges.mvc.MVCPortlet;

public class MyGreetingPortlet extends MVCPortlet {
    @Override
    public void processAction(
        ActionRequest actionRequest, ActionResponse actionResponse)
        throws IOException, PortletException {
        PortletPreferences prefs = actionRequest.getPreferences();
        String greeting = actionRequest.getParameter("greeting");

        if (greeting != null) {
            prefs.setValue("greeting", greeting);
            prefs.store();
        }

        SessionMessages.add(actionRequest, "success");
        super.processAction(actionRequest, actionResponse);
    }
}

Next, in view.jsp, add the liferay-ui:success JSP tag and add the taglib declarations below:

<%@ taglib uri="http://java.sun.com/portlet_2_0" prefix="portlet" %> 
<%@ taglib uri="http://liferay.com/tld/ui" prefix="liferay-ui" %> 
<%@ page import="javax.portlet.PortletPreferences" %>

<portlet:defineObjects />

<liferay-ui:success key="success" message="Greeting saved successfully!"
/>

<% PortletPreferences prefs = renderRequest.getPreferences(); String
greeting = (String)prefs.getValue(
    "greeting", "Hello! Welcome to our portal."); %>

<p><%= greeting %></p>

<portlet:renderURL var="editGreetingURL">
    <portlet:param name="mvcPath" value="/edit.jsp" />
</portlet:renderURL>

<p><a href="<%= editGreetingURL %>">Edit greeting</a></p>

After this change, redeploy the portlet, go to the edit screen and save it. You should see a nice message that looks like this:

Figure 3.7: The sample "My Greeting" portlet showing a success message

There’s also an equivalent utility class for error notification; it’s commonly used after catching an exception in the processAction method. For example:

try {
    prefs.setValue("greeting", greeting);
    prefs.store();
    SessionMessages.add(actionRequest, "success");
}
catch(Exception e) {
    SessionErrors.add(actionRequest, "error");
}

The error, if it exists, is shown in your view.jsp using the liferay-ui:error tag:

<liferay-ui:error key="error" message="Sorry, an error prevented saving
your greeting" />

If an error occurred, you’d see this in your portlet:

Figure 3.8: The sample "My Greeting" portlet showing an error message

The first message is automatically added by Liferay. The second one is the one you added in your JSP.