Javaspaces Example by Example

• Authors: Steven L. Halter
• Venue: Javaspaces Example by Example
• Year: 2001

From the Book:PrefaceWriting distributed programs is hard. This should not be a surprising statement to anyone who has had to deal with a distributed programming environment in the past. The good news is that every year it is getting a little bit easier as programming technologies and tools gradually catch up to the needs of a distributed environment. In particular, the introduction of JavaSpaces technology simplifies the distributed computing environment in several ways.JavaSpaces technology is a simple mechanism for performing distributed computing. In a distributed application, JavaSpaces provides a shared virtual space that providers and requesters of objects can use to communicate easily. This allows for the simple exchange of tasks, requests, and information in the form of Java objects. JavaSpaces also provides the ability to create and store objects with persistence.JavaSpaces is a Jini technology service. This means that developers working with JavaSpaces can also make use of the various Jini services, such as transactions and notification.JavaSpaces provides these capabilities with a very simple interface. Effectively making use of the simple interface, however, requires a number of tools, both conceptual and practical. This book should provide a solid base with a coherent set of examples to lead people in the right directions for using JavaSpaces technology.About This BookThe intended audience is for intermediate to advanced programmers wanting to learn about JavaSpaces. A working knowledge of Java is needed, and an acquaintance with Jini concepts is very useful, but not required.In this book, I have tried to give completeexamples for each of the concepts that are being discussed. OrganizationIn Part 1, "Getting to Know JavaSpaces," you look into the basics of using JavaSpaces. In Chapter 1, "About JavaSpaces" you explore what JavaSpaces are, how this book deals with them, and why anyone would want to use them. On the "what" side, the JavaSpace interface is presented along with some definitions of what the interfaces are. On the "why" side, the chapter presents some high level descriptions of the uses of JavaSpaces that are fleshed out in later chapters. Examples include using JavaSpaces as a mechanism for decoupled communication, application structuring, and parallel computing.In Chapter 2, "Obtaining and Installing JavaSpaces," you get JavaSpaces (and Jini itself) up and running. Doing this the first time can be a challenging experience. This chapter takes you through the process of installing Jini and JavaSpaces and running a simple application. In particular, some of the common problems, such as authorization configuration problems and improper codebase settings, are covered. Although an experienced Jini developer may skip this chapter, for beginners, this should be extremely valuable.In Chapter 3, "JavaSpaces Basics," you start to explore actually using a JavaSpace and writing some simple programs. It covers a simple method of locating a single JavaSpace. You then look at what an Entry is and how it can be used. Each concept is presented in the context of simple examples at this point.Chapter 4, "More JavaSpaces," will flesh out the more advanced topics of dealing with JavaSpaces. Again, each of the topics is covered in a simple example format. Later chapters make greater use of these. This chapter is intended to establish familiarity and building blocks for these topics.In Part 2, "Distributed Programming," you look at how you can apply the basics that you learned in Part 1 into writing distributed applications. In Chapter 5, "Encouraging Distribution," you start to explore programming in a distributed environment. Distributed programming is different than programming within a single machine (process). This chapter covers some of the concepts involved with programming in a distributed environment. In particular, it uses the concept of a linked list to explore some of the differences between distributed and nondistributed data structures.Chapter 6, "Preventing Deadlock," discusses mechanisms for allowing processes to avoid deadlock. This chapter covers locking and sharing issues and presents mechanisms, such as semaphores, for dealing with resource synchronization.Chapter 7, "Sharing Fairly," presents a more complex application example that makes use of (and ties together) many of the topics covered in earlier chapters. The application presents a small ordering processing system. This will be used to illustrate the concepts of sharing data in a fair and reliable manner.In Part 3, "Going to the Next Level," you look at how you can use the mechanisms you learned in Parts 1 and 2 and use these mechanisms to help meet demands that are needed to move into real world applications. Chapter 8, "Parallel Computing," looks into some of the areas where you can get into performance trouble and also some of the ways in which JavaSpaces can be an aid to performance. There are a number of ways to improve (or degrade) the performance of a distributed application. Some common techniques for doing this, such as how to decide what computations could benefit from being distributed and how to distribute data, are discussed in this chapter.Chapter 9, "Security Issues," looks into some of the security issues around JavaSpaces. There is currently no standard Jini security model. That does not mean, however, that your application can have no security itself. This chapter shows you how some of the security features of Java can be currently used with JavaSpaces. Setting up policy files and using some simple protocols to aid in application level security are discussed.Chapter 10, "Wrapping It up" ties up any loose ends. In it, you also briefly encounter some of the ways JavaSpaces are being used and might be used.