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The Portlet Packet: Inter-portlet communication in Portlet 2.0
Add dynamic interaction to your portal applications
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The Portlet 1.0 spec didn't do much to enable portlets to communicate, especially if they lived in different Web applications. Author Naresh Devnani shows you how all that has changed with the new Portlet 2.0 spec, with a new event model that makes it easier for portlets to talk -- and listen. Level: Intermediate
Portlet 2.0 is the recently finalized latest version of the Java portlet specification. One of the shortcomings of the previous version of the spec (JSR168) was lack of support for inter-portlet communication. As a result, developers tasked with presenting dynamic interaction on Web portals had to resort to all kinds of fancy workarounds.
The Portlet Packet: 3-for-1
This article is about the new inter-portlet communication facilities found in Portlet 2.0. See these other articles in the JavaWorld Portlet Packet to round out your education -- and look for future articles, too!
The Portlet 2.0 specification is designed to fill this gap with a revamped event model that allows portlets to publish and subscribe to events from other portlets. This article will explain the event model and walk you through some sample portlets that use this model to communicate.
Before you begin this article, you should already have some knowledge of portal programming. This article is intended for intermediate developers familiar with portlet development using the Portlet 1.0 spec, who want to learn about inter-portlet communication in Portlet 2.0.
The Portlet 2.0 event model
The portlet event model is a loosely coupled, brokered model that allows a portlet to react to state changes without direct user action with that portlet. These state changes may be generated from the container or from other portlets.
You could exchange information between portlets through portlet sessions in Portlet 1.0, but all those portlets would have to be part of same portlet application. With events, you can exchange information between portlets, even when they are not part of the same application. This is good, as enterprises use portlets from different sources (different vendors, for instance, or different development teams), and it becomes hard to contain them within same portlet application.
Examples and source code
In this article the Portlet 2.0 event model is introduced using a two sample Portlet 2.0 applications. The first application, jsrsample, has an event class that is created by a publishing portlet and consumed by a subscriber portlet. The second application, jsrsample2, only consumes the event created by jsrsample's publish portlet. You can download the source for these applications anytime.
Events are not only used for portlet-to-portlet communication; the portlet container can also raise events that can be consumed
by portlets. The Portlet 2.0 specification has some pre-defined container events, such as newWindowState and newPortletMode.
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Resources
- Download IPC-source.zip, the sample source code that accompanies this article.
- The example applications assume you have the JAXB library installed and are running in a JBoss Portlet Container 2.0, implementation, which includes Tomcat.
- Learn more about portlets with these articles in the JW Portlet Packet:
- Also see "Introducing the Portlet Specification, Part 1" (Stefan Hepper and Stephan Hesmer, JavaWorld, August 2003) for a fuller introduction to Portlet 1.0 -- the earlier version of the Portlet spec.
- Portlets are defined by the JSR 286 specification and Apache Pluto is the JSR 286 reference implementation.
- The Portlet Developer Discussion Group is an excellent resource for portlet developers. So is The Portal Zone.
More from JavaWorld
- Visit JW's Enterprise Java research center for more articles about enterprise Java programming tools and concepts.
- JavaWorld's community platform is growing: Check out JW Blogs and the improved Java Q&A Forums.
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This article provides good starting point for event model...By Anonymous on February 19, 2009, 5:30 amThis article provides good starting point for event model...
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