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Sun Microsystems has officially released Jini 1.0. The new technology promises to provide an architecture that lets network-connected devices using Java-based apps communicate with one another automatically.

Sun has pinned a lot of its hopes for the future of a networked electronics world — from computers to everyday appliances — on this culmination of the well-known Java vision. In its goal of “write once, run anywhere,” the “run anywhere” part is no more apparent than it is in Jini.

So what is Jini, and where does it want to go tomorrow?

First, we’ll take a look inside its special lantern. Then we’ll hear from the divines who have peered into its days ahead and are ready to auger.

The creators of Jini (pronounced ‘jee-nee’) have described it in this way: “Built on top of a Java software infrastructure, Jini technology enables all types of digital devices to work together in a community put together without extensive planning, installation, or human intervention. Each device provides services that other devices in the community may use. These devices provide their own user or programmatic interfaces, which ensures reliability and compatibility.”

Java inside

Except for the mention of Java, this sounds as if Sun could have cribbed this description from a 1964 World’s Fair tape. But then, Java is what makes the hype actually happen with Jini.

This is how it works. Jini offers Java class libraries for programming “services” across any network of processors using a Java VM — a so-called “federation” of machine and app “resources.”

“By leveraging Java, Jini provides simple distributed computing.”
– Bill Joy, Sun Microsystems

It does this, according to the folks at Sun, by taking advantage of the Java language’s remarkable combination of scalability and simplicity.

“By leveraging Java, Jini provides simple distributed computing,” Bill Joy, Sun co-founder and chief scientist told us. “We took the time to make it simple, and to identify a few basic concepts that are appropriate for distributed computing — remote objects, leasing, two-phase commit, events, and distributed security — [and] that we could teach Java programmers in just a couple of days to become Jini programmers.” He added that because Java developers can easily become Jini developers, they have “a huge head start on this.”

Joy said he believes Jini will be a vital technology for what is variously called “pervasive computing” or “ubiquitous computing.”

Building a federation

Here’s what you should have to get started with Jini:

  • A Java 2 VM — which includes Remote Method Invocation (RMI) enhancements needed by Jini
  • The Jini Starter Kit (see link in resources section)
  • A lookup service, or database for services available in the federation (an implementation is provided with the starter kit)
  • A discovery service, a protocol based on IP (unicast TCP and multicast UDP)
  • A properly functioning IP network.

No transaction processing manager is needed to use Jini technology, according to Sun. But if you want to use the distributed transaction services of Jini, you must have a transaction manager service running. Again, an implementation of this service is included with the Jini Starter Kit, though services can use whatever transaction manager they find appropriate.

(Jini’s distributed security framework is based on RMI and Java 2 platform security — a strong, capable model that applies equally to any Java-based program. Access Control Lists for Jini are in the works.)

From this, the programming model follows. Jini services use these primary conventions:

  • Distributed leasing provides a time-based model for activating and freeing services and resources.
  • Transactions allow wrapping of multiple operations on multiple services into a single unit of work that either completely succeeds or is rolled back.
  • Distributed events are a notification mechanism between services and resources that stretches beyond machine boundaries.

(Other key aspects of the programming model include: the Jini device specification, RMI, Object Serialization, and JavaSpaces. You will need to understand some of these specifications and provide implementations to interface methods to be able to write a service. Scads of documentation on the Jini programming model can be found on Sun’s Web site.)

With a Jini infrastructure in place and a basic understanding of the programming model under your belt, you are ready to write services.

As EarthWeb’s regular contributor Apu Shah explained recently, these can be aimed directly at machines, such as storage devices, or can be quite generic and provide a range of methods, much as class libraries do. (“In fact, you could have all computation-intensive code packaged in a service on a large machine where these methods execute most efficiently,” he commented. “This truly unleashes the power of distributed computing.”)

Sun offers the following examples of Jini services:

  • A printing service to print from Java and legacy apps
  • A JavaSpaces service for simple communication and storage of related groups of Java objects
  • A transaction manager to let groups of objects participate in the Jini Transaction protocol defined by the programming model.

(Collections of Jini services are referred to as “djinns.”)

The code for Jini falls under the new Sun Community Source License (SCSL) program. You can freely download (all whopping 35,000 lines of) it from Sun’s site.

Jini’s believers

Quite a lot has been written to date about Jini technically [see resources below]. So, in this section, we will look at its possibilities in the minds of its most ardent followers.

“Jini makes the concept of ‘plug and play’ really work.”
– Anne Thomas, Patricia Seybold Group

To begin, we asked leaders in the Java community to offer their analyses of Jini’s strengths.

Shah, who is director of software operations at Boston Education and Software Technologies, based in Mumbai, India, said: “Jini stands to provide a significant contribution to the networked world. With the service-based architecture that Jini provides, the greatest promise is that of spontaneous networking and availability. Simply adding a service implementation or plugging in a device to the network exposes the service to all clients in the Jini federation. No more configuration hassles, no more installation hassles, no more administration hassles. Clients become aware of new services and devices as they are added to the federation. Clients can use these services without having knowledge of where the service is located or how the service is implemented. It’s seamless and transparent to the client. This is Jini’s key strength.”

Anne Thomas, an industry analyst with the Patricia Seybold Group, in Boston, agreed with Shah that the new technology’s strong suit is its spontaneous networking capability.

“It’s really hard to make your PC talk to other types of devices,” she explained. “You need to load the right device driver — if you can find it — and somehow make sure that the new device doesn’t collide with some other device that you have defined to your machine. Jini makes the concept of ‘plug and play’ really work. Now imagine that you want to create a network of electronic devices in the home. Most households wouldn’t be willing to hire a network administrator to set up and maintain the at-home network. Without a working plug-and-play technology, networked homes will never exist. Some type of technology like Jini is essential to the success of the home network.”

Tim Rohaly, a software mage at the MageLang Institute, located nominally in San Francisco, said the key strength of Jini technology “is clearly the Java 2 platform itself.”

“[Jini] has the potential to be everywhere, in everything, and deliver the quality of service expected from consumer devices but sorely lacking in the predominant computing platforms of today,” he continued.

Rohaly said that when it comes to programming for devices, this usually means the use of expensive, proprietary, arcane environments that require specialized training and are not compatible with one another. “Java changes all that with APIs that span the range from smart cards to SMP machines,” he explained. “Capabilities inherent in Jini would be difficult, if not impossible, to implement in some other languages. Jini takes advantage of Java’s ability to build program capabilities by dynamically assembling objects from across a network.”

Jini’s challenges

What do the experts see as the chief obstacles for Jini’s acceptance and proliferation?

“Virtual machine deployment must increase significantly.”
– Apu Shah, Boston Technologies

Thomas said the principal hurdle for the technology to clear is the need for Java and Jini-enabled devices to become pervasive.

“You can’t rely on Jini until all the different computers and electronic devices actually get Java and Jini installed,” she observed. “I think it will be a while before we really see home appliances loaded and ready to go.”

Shah concurred: “Virtual machine deployment must increase significantly. There also must be significant support from Java device vendors to realize the dream of Jini.”

Rohaly said: “Jini is usable now for serious applications, but the realization of the complete vision will take a while. I don’t see obstacles as much as challenges — areas where the specs have deliberately left the details up to the marketplace and areas which utilize immature technologies, like wireless networking. In many ways this is what you want – it takes time and experience with any technology before you settle on an optimum way of achieving your goals. Sun has given Jini room to grow to fit the needs of the end users.”

He added that other “challenges” include the widespread lack of multicast-enabled IP service, at least on wide area networks, and integration with non-IP networks (Firewire, Bluetooth, USB, and so on). “The world is unlikely to be entirely IP based, so bridging and interoperability issues need to be addressed.”

Rohaly noted that the major trick for Sun is going to be in partnering and marketing in order to bring the vision to reality. “The technical challenges are minor compared to that. How successful Sun will be remains to be seen, but the cost of entry into Jini is so low that I imagine we will be seeing a lot of Jini-enabled software products in the near future.”

Sun’s Joy said the company is already well along in its efforts to build a “Jini community” of companies and organizations to define devices and services using the Java language and Jini distributed computing concepts. “There is an enormous amount of interest and much work to do in defining these new devices and services. Getting all this done as quickly as people want will be a challenge.”

A Jini community

Asked whether we could expect to see a grassroots movement of developers around Jini in the way Java was backed in its early days, the Seybold Group’s Thomas answered: “Absolutely, but I think it will be a smaller community. There are a lot fewer developers out there that write code at the system software level.”

“Software services will be deployed first, devices will be slower to show up, but it is inevitable that they will.”
– Tim Rohaly, MageLang Institute

Boston Technologies’ Shah noted that Jini has already created an enthusiastic community. “The Jini-users mailing list maintained by Sun enjoys significant traffic, with people from all around the world sharing ideas and thoughts about what Jini is and how it can be applied. I can already see the enthusiasm in postings. Jini facilitates the creation of communities working together spontaneously, remotely sharing information and passing on ideas, be it in software or humans.”

MageLang’s Rohaly concurred, saying that even though this nascent community has not reached great numbers yet, the early enthusiasts are “operating at a fairly high level.”

Rohaly himself may be one of the community’s most enthusiastic members. His bottom-line view of the new technology? “Potential for Jini is real; software services will be deployed first, devices will be slower to show up, but it is inevitable that they will. Not much hype here — just a lot of vision and a good solid technology that is capable of fulfilling that dream.”

Jini’s leader is just as upbeat about his offering’s chances. “We believe Jini can usher in an era of human-centered devices and services, which are simpler and bring ‘user delight’,” Joy concluded.


To get in on the action surrounding Jini, there is a users’ mail group. To subscribe, post a note to ‘’ and type in the body of the message ‘subscribe jini-users’. These are folks who are busily putting Jini through its paces as you read this. Then come back to Gamelan to discuss the new technology further in our Java Discussions Forum.

About the author

Kieron Murphy is the editorial manager for EarthWeb. He has previously written for The Java Report, JavaWorld, and IEEE Potentials, among other publications. He can be contacted at:

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