Wizard API updated!
Tim Boudreau has released a new version of the Swing Wizard library (version 0.997) that fixes the WizardException bug reported in JavaWorld's recent Open Source Java Project profile. The article's examples have been reworked to test out the new, improved WizardException. Thanks, Tim, for this helpful fix!
Open Source Java Projects: The Wizard API

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The skinny on Jini

Jini and JavaSpaces bring true distributed computing to Java

By Rawn Shah, JavaWorld.com, 08/01/98

By now you've read about Sun Microsystems's July 20 announcement of the release of Jini, its new technology for distributed computing. Sun released the specifications for Jini to the public, giving everyone the chance to delve into distributed programming.

To understand Jini, you'll need to know about JavaSpaces, because the two are carefully woven together. Further on in this article, you'll see that JavaSpaces is actually more important than Jini, but let's start at the beginning: What are these two technologies and what do they do?

  • Jini provides the distributed system services for look-up, registration, and leasing

  • JavaSpaces manages features such as object processing, sharing, and migration


JavaSpaces needs Jini to perform its functions. To use a military metaphor, Jini acts as a quartermaster allocating equipment and armaments to the JavaSpaces troops. The troops use the allocated equipment to carry out their orders in battle.

In this article, we'll provide an architectural overview of what Jini and JavaSpaces do and how they work together. Then we'll compare and contrast the Jini-JavaSpaces technology with similar technologies. And, finally, we'll explain how this technology can be used and where it will be most beneficial.

The details on Jini

As Sun puts it, Jini allows you to create a "federation" of devices and software components in a single distributed computing space. Although the components work together to serve a common goal, they're still identified as separate components on a network. The federation provides services that are accessed by the various devices and software components. By services we mean communication mechanisms, users, hardware devices, storage devices, calculators (i.e., for your spreadsheet), notepads (for your BBS), and so on. The various members of a Jini federation share their services to get a job done. They communicate with each other through a set of Java interfaces known as the service protocol, and they locate each other using a special look-up service. The look-up system works in a multipoint network environment and the different components are ordered in a hierarchy.

The low-level communications used by Jini is the Java Remote Method Invocation (RMI) API as specified in JDK 1.2. There are a few basic changes between RMI in JDK 1.1 and 1.2 that better support the Jini system, particularly object activation, and distributed garbage collection. Jini requires RMI in the new JDK. The current specification documentation is slightly off when it says "extended RMI"; there are no extensions to RMI specifically for Jini other than what is already in JDK 1.2.

Each component has an ACL (access control list) describing which other components are allowed access to it. The component that sends out a service request, known as the principal, communicates with other components needed to perform a service.

The look-up service, distributed security system, RMI 1.2, and the discovery protocol (to register or locate a service using the look-up service) together constitute the infrastructure component of Jini.

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Resources
  • Sun's Jini home page http://java.sun.com/products/jini/index.html
  • The real meat of the matter, the Jini specification http://java.sun.com/products/jini/specs/index.html
  • Sun's JavaSpaces home page http://java.sun.com/products/javaspaces/
  • The JavaSpaces specification http://java.sun.com/products/javaspaces/specs/index.html
  • Read all about the Object Management Group and CORBA http://www.omg.org
  • Lucent Technology's Inferno system http://www.lucent-inferno.com/Pages/Developers/index.html
  • The PVM home page http://www.epm.ornl.gov/pvm/pvm_home.html
  • This online book will familiarize you with PVM in detail http://www.netlib.org/pvm3/book/pvm-book.html
  • "Do-It-Yourself Supercomputers", Wired News, July 3, 1998 http://www.wired.com/news/news/technology/story/13440.html
  • DATEK, an enterprise resource planning application vendor, announces the first distributed application integrated with Javaspaces and Jini http://www.internetwire.com/technews/tn/tn980741.htx
  • Check out News.com's report on Jini, "Sun makes another run at Windows," which debuted just before its release http://www.news.com/News/Item/0,4,24214,00.html