Java Reference
In-Depth Information
Sidebar 13.1 Java RMI
Java RMI is a middleware framework that allows a client application to invoke a method of an
object residing in a different address space, i.e. that is a remote object. Let's consider the example
depicted in the figure below. Classes
Naming
,
Remote
and
UnicastRemoteObject
are provided by the
Java RMI package. Classes
SumStub
and
SumSkeleton
are automatically generated by the RMI com-
piler. The other classes are defined by the programmer.
The
Client
object and the
Server
objects reside on two different networked computers, each one
being identified by a unique IP address. The
Server
creates an object of class
SumImplementation
that exports the
int sum(int a, int b)
method defined in interface
SumInterface
. The RMI framework
allows a
Client
to invoke the sum method on a
SumImplementation
object by passing its actual
parameters and getting the result.
This is accomplished by means of two ancillary objects called the
SumStub
and the
SumSkeleton
.
The
Stub
is a surrogate (proxy) of the remote object and resides in the client's address space. It
offers the same set of operations as the remote object, i.e. the
sum
method. The
Stub
is in charge of
marshalling the client's request and transmitting it through the network. The
Skeleton
resides in
the
Server
address space and is in charge of receiving and unmarshalling the client's request and of
invoking the corresponding operation of the
SumImplementation
object. The matched pair
Stub
Skeleton
is automatically generated at compile time from the definition of
SumInterface
.
In order to make the
SumImplementation
object accessible from a remote application, the
Server
must register it with a symbolic name using the
Naming
class's
bind
method. Once a remote object
is registered on the local host, clients on a remote host can look up the remote object by name
using the
Naming
class's
lookup()
method, obtain its reference and then invoke remote methods on
the object.
Naming
void bind(String name,
Remote obj)
Remote lookUp
(String name)
Client
Server
execute()
execute()
Remote
UnicastRemote
Object
SumInterface
int sum(int a, int b)
SumStub
SumSkeleton
SumImplementation
int sum()
int sum(int a, int b)
int sum(int a, int b)
