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Summary

In this chapter, you learned that a Jini system is made up of three parts: Service Client Service locator Code is moved between these applications. A registrar acts as a proxy to the lookup locator and runs on both the client and service. A service and a client both possess a certain structure, which is detailed in the following chapters. Services may require support from other non-Jini servers, such as an HTTP server.

ini is advertised as being network plug and play, which carries with it the idea of zero administration, where you buy a device or install a software service, switch it on, and voila! it is there and available. Well, this may happen in the future, but right now there are a number of backroom games that you have to succeed at. Once you have won these games, network plug and play does work, but if you lose at any stage, you have an uphill battle to fight. The difficult parts are getting the right files in the right places with the right permissions. About 50 percent of the messages in the Jini mailing list relate to these configuration problems, which shouldn t occur. This chapter looks at some of the problems that can arise in a Jini system, most of which are configuration issues of some kind. Each of the early sections contains step-by-step instructions on what to do to get the example programs working. Because this is only the second chapter in this book, and right now you shouldn t have managed to fail at anything, feel free to skip to the next chapters, but do come back here when things go wrong.

The following is a typical Java package-related error: Exception in thread "main" java.lang.NoClassDefFoundError: basic/InvalidLookupLocator Most of the code in this tutorial is organized into packages. To run the book s examples, the classes must be accessible from your classpath. For example, one of the programs in the basic directory is InvalidLookupLocator.java. This defines the class InvalidLookupLocator in the package basic. The program must be run using the fully qualified path name, as follows: java basic.InvalidLookupLocator (Note the use of . , not / .) To find this class, the classpath must be set correctly for the Java runtime. If you have copied the file classes.zip, then you can find the class files for this tutorial there. You only need to reference this: CLASSPATH=classes.zip:...

If you have downloaded the source files, then you can find the class files in subdirectories such as basic, complex, and so on. After compilation, the class files should also be in these subdirectories, for example, basic/InvalidLookupLocator.class. An alternative to using classes.zip is to set the classpath to include the directory containing those subdirectories. For example, if the full path is /home/jan/classes/basic/InvalidLookupLocator.class, then set classpath to CLASSPATH=/home/jan/classes:... An alternative to setting the CLASSPATH environment variable is to use the -classpath option to the Java runtime engine: java -classpath /home/jan/classes basic.InvalidLookupLocator

There are five versions of Jini: 1.0, 1.1, 1.2, 2.0, and now 2.1. The core classes are the same in each version. In this book, we ll deal only with the new version, 2.1. Jini 2.1 requires Java Development Kit (JDK) 1.4 or later, not earlier versions of Java. It will work with JDK 1.5 but does not require it. The changes for 2.1 are listed in the document jini2_1/doc/release-notes/new.html. The main classes that have changed for 2.0 are as follows: LookupDiscovery (now has an additional constructor) LeaseRenewalManager ServiceIDListener The main new classes are as follows: LookupLocatorDiscovery LookupDiscoveryManager ClientLookupManager If you get syntax errors or runtime errors relating to these classes, it is possible that you are using Jini 1 instead of Jini 2. If you get deprecated warnings, it is likely that you are using the Jini 1 classes in a Jini 2 environment. The old classes are supported for now, but are not approved.