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Fiddler

A new member of the family since Jini 1.1, Fiddler is a lookup discovery service. Once a client finds a service registrar, it usually wants to perform useful work that doesn't necessarily include bookkeeping registrars. On the other hand, a client does want to make sure that it talks to registrars that actually exist, so the bookkeeping is a necessary activity.

Just as business people outsource bookkeeping to accountants, Jini clients can outsource the bookkeeping of lookup services to lookup discovery service. This is an important pattern in Jini: if you see common behavior, don't just refactor it into a separate class or package, refactor it into a separate service.

Fiddler can be run as an activatable service (the recommended and default way) that keeps a persistent transaction log between starts, or as a service started directly from the command line without persistence.

Mercury

Another new entry is Mercury, a Jini event mailbox. Activatable (and other) services are not always available, and mobile services may actually be physically removed from the network altogether. Event registrations may be problematic in this case: an activatable service would be activated for every event sent to it and a mobile service simply wouldn't get them. Mercury acts as an intermediary, collecting events on behalf of clients and only sending them when the client explicitly requests it. An activatable service thus can disable event delivery when it deactivates, and request delivery of all outstanding events right after it is activated again.

Norm

Norm, also new since Jini 1.1, implements another boring bookkeeping activity: lease renewal. There was already a local utility class for this, but activatable and mobile services may not always be available to renew their leases in time. Therefore, they hand their leases over to Norm, who will take care of the job so the services may safely become inactive.

Norm is an activatable service and keeps a persistent transaction log of leases and registrations.


 
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