دانلود کتاب JavaSpaces in Practice

For several years, Sun has promoted Jini as a means of developing Java-based distributed computing systems. As a practical matter, these systems are often mobile, and hence wireless. Think perhaps of the increasingly powerful and ubiquitous cellphones, PDAs and laptops. Less familiar to the public, but even more pervasive, are products using embedded microprocessors like cars and home appliances. Typically, most distributed systems have less memory and power than conventional computers, and their network connections may be intermittent. Developing applications to run under these conditions is tough, and Jini tries to make it practical. But in the last two years the pace of Jini development seems to have slowed. A rival open source approach, JXTA, has quickly grown and captured a lot of mindshare amongst developers. Its proponents say that it is far easier to learn and use. Naturally, Jini enthusiasts strongly disagree.But for the sake of argument, suppose Jini is indeed more difficult to program. Then if you are Sun, it makes sense to develop useful utilities on top of Jini that simplify coding. JavaSpaces, for example. Which is the subject of this book. It is a Jini service (=utility) that can be easily used by other devices on the network. A JavaSpace holds data that can be read and altered in a transactional context. This means that if the set of operations in a transaction fails, it can be rolled back; a fundamental necessity in a distributed system, where things can fail in many ways. As the authors clearly demonstrate, you need know little Jini to understand and use JavaSpaces. The interface is very clean, having essentially only three operations: "write" - to put something into the space; "read" - to read an item from the space into your device; "take" - to read the item into your device and remove it from the space.The book is short and succinct. The code examples are easy to grasp, without being simplistic. If you have been thinking about using Jini, or perhaps you already are using it, but are stymied, then try this book. In a day's reading, you can get its essence. A low risk investment of your time.Suppose though that you are a JXTA programmer. Or maybe you are using some other third way to develop distributed applications. There is probably no analog of JavaSpaces in your environment. Consider investing a day of your time in this book. See if it makes sense of have something like this. If so, perhaps you should implement it?