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Jini
Technology Infrastructure: Lookup Service
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The Jini Lookup
Service is essentially a bulletin board repository for all services available
on the network. It constantly searches for Discovery packets and allows those
services to register (of Join), enabling the service and its interface to
become a part of the overall Jini community. Characteristics uploaded into
Lookup Service include all value-added services provided by the device or
application, such as drivers, help wizards, attributes, and so on. The Lookup Service then stores discovered
services as an extensible set of Java application objects, including all of
the information/attributes of those services.
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For example,
when a printer registers with the Lookup Service, it loads a printer driver
or an interface to the driver into the Lookup. Then when someone wants to use
that printer, he or she downloads the driver and driver interface from the
Lookup onto their client device. The printer might also load other
value-added services into the Lookup Service. For example, the printer might
offer color printing, or support for PostScript. It might also have help
wizards that will run on the client device.
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Its important to
note that service objects are only downloaded as required. Objects in a
lookup service may include other lookup services -- thus providing
hierarchical lookup. Further, a lookup service may contain objects that
encapsulate other naming or directory services, providing a way for bridges
to be built between a Jini technology’s Lookup Service and other forms of
lookup service.Of course, references
to the Lookup Service may be placed in these other naming and directory
services, providing a means for clients of those services to gain access to a
Jini technology federation.
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Lastly, a
service is added to the Lookup Service by a pair of protocols called Discovery
and Join — first the service locates an appropriate lookup service
(by using the Discovery protocol), and then it joins it (by using the Join
protocol). The basic Lookup
Service interface provides all that is needed — registration, access, search,
and removal functions.
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