As announced here by Sun's Onno Kluyt last week, March 23-25 sees the latest meeting of the community that has grown around Jini - the Java-based network technology that enables adaptive network-centric services based on shared memory (JavaSpaces) and code portability.

For more information and for registering, interested developers can visit here. The event is being held in Boston, MA.

Jennifer Kotzen, senior product marketing manager for Jini at Sun, has been talking about the technology - which Sun hasn't yet used in any products, although it does use it in the development of products for dynamic connectivity services.

"Sun believes Jini's time is arriving, thanks to the advent of concepts such as grid, utility, and on-demand computing and with service-oriented architectures," Kotzen said.

"Sun responds to market demands, and what we have seen is that the need that Jini technology fulfills has not been pressing until recently," she added. "The changing marketplace is expected to result in a corresponding increase in use of Jini technologies by Sun and its competitors." The concepts behind Jini involve distributing compute cycles and services around a network on an as-needed basis, without particular regard to the origin of the cycles. Scott McNealy in his 2004 technology predictions didn't mention Jini, but has recently said:

        "There's a huge community built around [Jini]. It's getting embedded here, there, and everywhere."

Below is an extract from the "Jini and JavaSpaces" section of Karl McCabe's recent JDJ article, "Java and the Future of Ad Hoc Networking":

Jini, officially launched in mid-2000, is a technology that may be used to federate groups of users and resources required by those users. It aims to allow a network to be more flexible and more easily administered, with resources being easily located by humans and computational clients. Jini provides framework components for managing federated services, such as a lookup service for locating services, a leasing capability for controlling use of services and security, and transaction capabilities for coherent interservice interactions.

Jini operates at a level of abstraction that makes it attractive to application developers who need to solve an application problem, rather than worry about underlying networking issues. It provides a paradigm that may be useful to Bluetooth applications, since it allows services to be loosely coupled, that is, Jini nodes and services may appear and disappear from a network as a natural consequence of its operation. This loose coupling of entities is an important quality in a mobile ad hoc network.

JavaSpaces is a Jini service. It provides the abstraction of a JavaSpace into which components known as "entries" can be put. An application may "find" these entries, it can "read" (passive) or "take" (destructive) entries, and it may write entries to a space. The JavaSpaces architecture includes a notification mechanism that notifies an application when an entry is written that matches some criteria. This form of abstraction is particularly useful for passing information from stage to stage in a workflow model, or for applications where redemption of some token is important - for example, redeeming a voucher with a service provider. Interestingly, JavaSpaces also provides a useful abstraction for layering over actual physical spaces. In a Bluetooth access point scenario, this may be useful as an application model for mapping zones or spaces in which access points are installed, and for specifying which services are available in which zones.

Both Jini and JavaSpaces are good examples of creative and elegant designs for Java software frameworks that are intended to provide rich abstractions to application programmers. They have characteristics that make them well suited to ad hoc networking applications - particularly the inherently loose coupling of objects. They're not without their drawbacks, though, as I'll examine shortly.