Tutorial:Internet
Understanding Jini
Often quoted and misunderstood in equal measures, Sun's Jini promises to extend the boundaries
of network computing by combining Java with Jini and its sibling JavaSpaces.
By Clive Grace
T
he promise at the heart of Java
Jini can thus be logically divided
cuted remotely, and when a method is
has always been code that de
into three loose areas: an infrastruc
incompatible with its execution envi
velopers can write once and run
ture; a programming model; and Jini
ronment (floating point code, for ex
anywhere but with smart card to su
services. To the rest of us this looks
ample), it simply loads the correct
percomputer scalability.
awfully like a network operating sys
method automatically and discards it
Sun has recently encountered criti
tem, but Sun is justifiably playing
when it is not needed.
cism of Jini's performance, primarily
down its role as a true network OS
Jini supports only very simple basic
from Microsoft (mainly for technical
primarily because Jini only provides a
control structures. Objects communi
reasons, but ostensibly because it in
limited selection of core services. Also,
cate via the standard Java RMI inter
conveniently clashes with Millennium,
some of Sun's partners (in particular
face through basic operations in what
Microsoft's quiet project to develop its
companies with their own network OS
Sun
has
dubbed
JavaSpaces.
own version of a distributed operating
products such as Novell) are wary of
JavaSpaces is a vital part of Java that
system).
helping Sun develop a potentially self
manages lower level features such as
Nevertheless, Jini represents a ster
competing network OS.
processing objects and sharing them
ling attempt by Sun and its supporters
with other processes and so on.
to help make Java truly portable while
Differences
To understand Jini, then, you'll
simultaneously addressing many of
need to know about JavaSpaces, be
Java's limitations as a language capa
So how does Jini differ from a tradi
cause the two are carefully woven to
ble of running on the smallest hand
tional network OS? Jini has the poten
gether. JavaSpaces is actually more
held PC to controlling huge pieces of
tial to create large federations of
important than Jini, because although
equipment, yet with few developers
electronic appliances, which you can
JavaSpaces manages features such as
actually using it in the real world.
connect to a standard PC. You can al
object processing, sharing and migra
ternatively obtain these services (such
tion, Jini provides the distributed sys
What Is Jini?
as memory, storage, and enough proc
tem services for look up, registration
essing power to manage the contents
and leasing.
At its very simplest, Jini is an archi
of the former) from the network itself.
JavaSpaces needs Jini in order to
tecture for a network operating system
Jini thus differs from traditional
perform its functions. Jini allocates fea
designed for an array of electronic de
network OSes because it tends to be
tures and services to the JavaSpaces
vices and software services. This takes
quite small. Core Jini components re
model, which then uses its allocation to
it out of the domain of the typical PC
quire only a Java virtual machine,
carry out its coded instructions.
or network computer into the realm of
about 4 KB of resident memory, and
However, the most fundamentally
the network appliance.
some processing to drive it. Initial Jini
important feature associated with Jini
Appliances can be anything from a
systems weigh in at about 0.5 MB. It is
is that it provides Java with plug and
telephone or pocket organiser or even
also fully object based, ie, its compo
execute capabilities. Sun hopes that a
something less obviously a computer
nents include methods that can be exe
new device will gain instant recogni
such as a remote control unit (imagine
a remote control that changes its func
tions depending on what room you are
in). The dream of Jini is to run on any
Sun tries not to define Jini as a network
appliance or computer or rather, any
device that supports Java.
operating system, preferring instead to
Sun tries not to define Jini as a net
work operating system, preferring in
call it a networking infrastructure
stead
to
call
it
a
networking
infrastructure running on top of Java
running on top of Java.
to create a federation of virtual ma
chines.
Issue 108 (June 1999) page 9
File: T1824.1
PC Network Advisor
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