Portlet Creation Made Easy Part -II

Inter Portlet Communication using IPC Story Board

Contributed by Umachithra Damodaran
Jun 2007

The Inter Portlet communication for Sun Java System Portal Server was achieved through the proprietary API's which was an extension to JSR-168 Portlets. Using this API, JSR-168 portlets will be able communicate with each other even if they are in different web applications. It is assumed that all these portlets will be on the same instance of a Portal Server and running inside the Portal Server Portlet container.

1 Inter Portlet Communication API

This API uses event generation and notification to convey the information/data among portlets. The event notification will be for the portlets which have registered themselves for listening to that particular event.

1.2 Event Generation and Subscription

Inter Portlet communication consists of an Event Generator Portlet and Event Subscriber Portlet. The Event Generator portlet triggers an event through its processAction() method. Portlets interested in receiving the event(Event Subscriber portlet ) will listen to the event and perform some action in response to the event.

In order to listen and respond to the event the Subscriber portlet has to implement an interface called PortletEventListener. This has the handleEvent() method ,which will be called if and only if an event is fired and the portlet has subscribed to listen to that event. The subscriber portlet can opt to throw a new event from the handleEvent() method.

In addition to this, all the portlets which are interested in generating or subscribing an event must declare it in the sun-portlet.xml file under <generates-event></generates-event> and <consumes-event></consumes-event> tag.

2 IPC StoryBoard

The IPC StoryBoard currently supports the JSR 168 inter portlet communication and in future will also support the Eventing feature of JSR 286.

2.1 Installing IPC Story Board Plugin

Download the plugin from http://portalpack.netbeans.org/download.html and follow the install instructions to install the plugin.

3 Creating Communicating Portlets using IPC Story Board.

A Fund Transfer example is taken to show the Inter Portlet Communication. The FundTransfer Portlet fires an event ,when a transfer operation takes place.AccountBalance_A portlet consumes the event fired by FundTransfer Portlet and reduces the balance of Account A. This in turn fires a new event which is consumed by AccountBalance_B portlet,which increases the balance with the amount transferred.

3.1 Create a Event Generator Portlet

1.Create a new Portlet Application by selecting, New Project ->Portlet Applications -> JSR 168 Portlet Application in the Netbeans IDE .

2.Enter the name of the Portlet and other valid data required and click Finish.

3.The Portlet Application is created with all the files required by the JSR168 specification for portlet. Now ,if you expand the portlet.xml file ,you would see all the portlets listed in the application as nodes. This is a new feature introduced in this plugin.

4. Edit and update the FundTransfer_view.jsp with the following code:

<%@ taglib uri="http://java.sun.com/portlet" prefix="portlet" %> <portlet:defineObjects/> <form action="<portlet:actionURL />" method="POST"> <table border=1> <tr><td colspan="2"><b>Internal Funds Transfer</b></td></tr> <tr><TD>From Account No</TD><TD>12345</TD></tr> <tr><TD>To Account No</TD><TD>67890</TD></tr> <tr><TD>Amount</TD><TD><input type="text" name="amt" size=15></TD></tr> <tr><TD><input type="submit" value="Transfer" ></TD></tr> </table> </form>

5. Choose the Portal Server on which the portlet application should be deployed.

a.Select the Portlet Application under the Projects tab ,right click and choose properties.

b.Select the category “Run” and choose the “Open source Portlet Container Driver” / “Sun Java System Portal Server 7.x” in the drop down box for “Server” and click Ok.

3.2 Create the Event Subscriber Portlet

Create a second portlet called AccountBalance_A ,following the steps mentioned above.

a.Add a class variable “ double balance=200000;”

b.update the doView() method as follows :

public void doView(RenderRequest request, RenderResponse response) throws PortletException,IOException { response.setContentType("text/html"); PrintWriter writer = response.getWriter(); writer.println("<h4>Banlance For Account 12345 is :</h4>"+balance); }

Similarly, create another portlet called AccountBalance_B and follow the steps mentioned above and provide a different value for balance.

3.3 Storyboard

Invoke the storyboard by selecting Window->"IPC Storyboard" option in IDE. Now select the FundTransfer node ,under the portlet.xml and drag into the story board. Similarly , drag the AccountBalance_A portlet into the storyboard.

3.4 Adding an event to the Event Generator Portlet.

Select the FundTransfer Portlet inside the storyboard and right click and choose the option “Add Event”. It will create a Event called “New_Event”.Double click the event created and rename it as “transfer”.

This will insert the following tags in the sun-portlet.xml file.

<portlet> <portlet-name>FundTransfer</portlet-name> <events> <generates-event>transfer</generates-event> </events> </portlet>

3.5 Generate the Source for the event

Now select the event created and right click and choose the option “Generate Source”. It pops up a window ,where you can choose to add the source generated inside the processAction method or in a new method. Choose to add inside the processAction method by selecting the option “Add to existing source”.

You will now see that the processAction() is updated with the following code.

try{ String eventData = ""; PortletEventBroker peb = new PortletEventBroker(request); PortletEvent pe = peb.createEvent("transfer"); pe.setEventData(eventData); pe.fire(); } catch(Exception e) { //TODO Catch Exception here }

Change line 2 to String eventData = request.getParameter("amt");

3.6 Link the Event to the Subscriber

Select the event in the FundTransfer Portlet in the storyboard and drag and drop the event on the AccountBalance_A portlet. This will link the event to the subscriber as shown below.

It also adds the following tags to the sun-portlet.xml file.

<portlet> <portlet-name>AccountBalance_A</portlet-name> <events> <consumes-event>transfer</consumes-event> </events> </portlet>

3.7 Generate Consume Event Source

Select the consume_transfer event in the AccountBalance_A portlet in storyboard and right click and choose the option “Generate Consume Event Source”. This pops up a window where you can specify the name for the method to be invoked when the event is fired.

As a result , the AccountBalance_A portlet imports the corresponding packages and implements the PortletEventListener interface and overrides the handleEvent() with the following code.

public void handleEvent(EventRequest eventRequest, EventResponse eventResponse) { if(eventRequest.getEventName().equals("transfer")) { handleConsumetransferEvent(eventRequest,eventResponse); } } private void handleConsumetransferEvent(EventRequest eventRequest, EventResponse eventResponse) { Object eventData = eventRequest.getEventData(); if(eventData != null) { //Set EventData Object in portlet session eventRequest.getPortletSession(false).setAttribute("transfer", eventData, PortletSession.PORTLET_SCOPE); //uncomment this line if you want to set the EventData as string in render parameter //eventResponse.setRenderParameter("transfer",eventData.toString()); } }

Now update the method created with the following code:

private void handleConsumetransferEvent(EventRequest eventRequest, EventResponse eventResponse) { Object eventData = eventRequest.getEventData(); if(eventData != null) { double amt=Double.parseDouble(eventData.toString()); if(amt < balance) { balance -=amt; } else { //TODO } } }

Based on the amount transferred (if its greater than balance) ,the AccountBalance_A portlet can fire another event which will be consumed by AccountBalance_B portlet.(This shows that event can also be generated from a handleEvent())

In order to fire a new event from AccountBalance_A portlet,Select the AccountBalance_A portlet in the storyboard, right click and choose “Add Event”and then rename the newly created event to creditBalance. Generate the source for the event. It will create the following code.

private void generatecreditBalanceEvent(ActionRequest actionRequest, ActionResponse actionResponse, String eventData) { try{ PortletEventBroker peb = new PortletEventBroker(actionRequest); PortletEvent pe = peb.createEvent("creditBalance"); pe.setEventData(eventData); pe.fire(); } catch(Exception e) { //TODO Catch Exception here } }

Note ** Change the argument of the generatecreditBalanceEvent to (EventRequest eventRequest, EventResponse eventResponse, String eventData)

Invoke the generatecreditBalanceEvent() from handleConsumetransferEvent() to fire the new event.

if(amt < balance)  { balance -=amt; generatecreditBalanceEvent(eventRequest,eventResponse,eventData.toString()); }

Next step is to consume this event in the AccountBalance_B portlet. Drag the creditBalance Event into the AccountBalance_B portlet and generate consume event source . Update the source created with the following code.

private void handleConsumecreditBalanceEvent(EventRequest eventRequest, EventResponse eventResponse) { Object eventData = eventRequest.getEventData(); if(eventData != null) { balance+=Double.parseDouble(eventData.toString()); } }

Finally clean ,build and deploy the portlet on the PortletServer. On accessing the portlets, you will find all the three portlets displayed as follows.

Enter an amount in Fund Transfer portlet and click transfer. You will find that the AccountBalance_A is reduced by the transfer amount and AccountBalance_B be increased by the same amount.

4 Example Source Code

5 References

     Portal Pack IPC Story Board

Portlet Creation Made Easy – Part 1