2.10 Listeners

2.10 Listeners

The event model of the Portal API is very similar to the traditional Java event model. However, there are two main points of distinction. First, there is no need to register listeners. When a portlet in installed, the Portal Server determines the listeners it implements and registers them on behalf of the portlet. Secondly, since the registration is taken care of by the Portal Server, it is not possible to specify which portlets a particular portlet wishes to register for. Therefore, portlets implementing listeners need to carefully plan for unsollicited and unexpected events.

There are several listeners defined in the Portal API. The ActionListener is covered in the Event handling section and the MessageListener is covered in the Messaging section.

2.10.1 PortletTitleListener

This listener allows you to dynamically set the title of the portlet. This listener requires the single method as shown in Example 2-20. This interface is particularly useful when tailoring the title to certain modes or devices. To return a title, simply use a PrintWriter object or include a JSP using the PortletContext object. While the second approach allows you to create a more dynamic title including images and so forth, you must remain mindful of the limited space in the title bar.

Example 2-20. PortletTitleListener example

public void

doTitle

(PortletRequest request, PortletResponse response)

                   throws PortletException, IOException {

   PrintWriter out = response.getWriter();

   String title = getPortletSettings().getTitle(

                   request.getLocale(), request.getClient());

   out.print(title + "(" + request.getMode() + ")");

}

2.10.2 PortletPageListener

This interface provides the opportunity to add content to the top and bottom of the aggregated page. Example 2-21 on page 96 illustrates a simple implementation of the PortletPageListener interface. It is important to note that content returned from the beginPage method is not placed at the top of the page but rather at the top of the aggregated content as displayed in Figure 2-13.

Example 2-21. PortletPageListener implementation

public class AgendaPortlet extends PortletAdapter implements

PortletPageListener {

........

   public void beginPage(PortletRequest request, PortletResponse response)

                throws PortletException, IOException {

      PrintWriter out = response.getWriter();

      out.println("This page contains my agenda.");

   }



   public void endPage(PortletRequest request, PortletResponse response)

                throws PortletException, IOException {

      PrintWriter out = response.getWriter();

      out.println("End of my agenda.");

   }

}

The resulting page including the top and bottom messages is illustrated in Figure 2-13.

The beginPage is a convenient method when you need to include Javascript functions needed by your portlet. However. be very conscious of any content you decide to display in the beginPage method as it may adversely affect the overall aggregation of the page. Furthermore, because the page is aggregated, be sure that any functions or global variables you declare have properly encoded the namespace of the portlet to ensure there are no naming collisions. Use the response.encodeNamespace to do this.

Restriction

The Home.jsp can choose to cancel calls to the PortletPageListener via the <wps:pageRender includeBeginPage="no" includeEndPage="no"> tag. In this case, your beginPage and endPage methods will not be called.

public void

login

(PortletRequest request) throws PortletException{ ... }

public void

logout

(PortletSession session) throws PortletException{ ... }

public void

windowMaximized

(WindowEvent arg0) throws PortletException {

   // Some action can be performed



}

public void

windowMinimized

(WindowEvent arg0) throws PortletException {

   // Some action can be performed



}

public void

windowRestored

(WindowEvent arg0) throws PortletException {

   // Some action can be performed



}

public void

windowClosing

(WindowEvent arg0) throws PortletException { }

public void

windowClosed

(WindowEvent arg0) throws PortletException { }

public void

windowDetached

(WindowEvent arg0) throws PortletException { }