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 Jxta solution to P2P

Sun's new network computing platform establishes a base infrastructure for peer-to-peer application development

By Navaneeth Krishnan, JavaWorld.com, 10/17/01

Today's Internet is witnessing a revolution. A revolution that strives to change one of its basic features. A revolution where network endpoints -- or clients, such as desktop PCs, mobile phones, PDAs, and the like -- are demanding better network status. A revolution fueled by applications like Napster and Gnutella, applications that bring an end to a server-dominated Internet. A revolution hailed as P2P.

P2P (or peer-to-peer) networking is a network model where, depending on an operation's context, any node can operate as either a server or a client. P2P provides certain interesting capabilities not possible in traditional client/server networks, which have predefined client or server roles for their nodes.

In this article, I introduce you to P2P networking and compare it with client/server networking. I also introduce you to Jxta (pronounced jux-ta), a P2P computing platform pioneered by Bill Joy, Sun Microsystems' chief scientist and corporate executive officer; currently, Jxta is being molded by hundreds of open source developers. Jxta holds tremendous promise for the P2P world. It defines a set of protocols that developers can use to build almost any P2P application. At the same time, these protocols are flexible enough to be easily adapted to application-specific requirements. While Jxta does not dictate any particular programming language or environment, Java could potentially become the language of choice for P2P application development for obvious reasons: portability, ease of development, and a rich set of class libraries.

P2P: An overview

Today, the most common distributed computing model is the client/server model. Figure 1 depicts the typical client/server architecture.

Figure 1. The client/server model

In the client/server architecture, clients request services and servers provide those services. A variety of servers exist in today's Internet -- Web servers, mail servers, FTP servers, and so on. The client/server architecture is an example of a centralized architecture, where the whole network depends on central points, namely servers, to provide services. With no servers, the network would make no sense; without them, how would Web browsers work? Regardless of the number of browsers or clients, the network can exist only if a server exists.

Like the client/server architecture, P2P is also a distributed computing model, but there is an important difference. The P2P architecture is a decentralized architecture (see Figure 2), where neither client nor server status exists in a network. Every entity in the network, referred to as a peer, has equal status, meaning that an entity can either request a service (a client trait) or provide a service (a server trait). Figure 2 illustrates a P2P network.

Figure 2. The peer-to-peer model

Though peers all have equal status in the network, they don't all necessarily have equal physical capabilities. A P2P network might consist of peers with varying capabilities, from mobile devices to mainframes. A mobile peer might not be able to act as a server due to its intrinsic limitations, even though the network does not restrict it in any way.

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