Java Remote Method Invocation (RMI)

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Java Remote Method Invocation (RMI)
In Java we implement object systems
O1
O2
O3
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Programs/objects running on different virtual
machines separately compiled/linked allocated
in different address spaces ? object by value
message passing Approach (very natural in
object technology) definition of behavior ?
interface implementation of behavior ? class
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The concept
client object
client object
STUB
SKELETON
server object
server object
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RMI architecture layers
client
server
stubs skeletons
stubs skeletons
RMI system
remote reference layer
remote reference layer
transport layer
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Stubs plays the role of PROXY Skeletons he
lper class generated automatically (Java 2
new protocol reflection classes ? no
skeleton class)
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Remote Reference Layer (RRL) RRL defines the
invocation semantics Connections unicast,
point-to-point (currently) Stages server
instantiates service exporting to
RMI optional naming and registering (Java 2
activable remote object (i.e. on-demand
instantiation)
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network cable
Transport layer
JRE
JRE
JRE
JRE
Host OS
Host OS
Network layer
Network layer
On TCP/IP Java Remote Method Protocol
(JRMP) Other proprietary protocols are also in
use!! (Java 2 v1.3 RMI-IIOP (straight link to
CORBA))
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Naming The big question How can a client find a
particular service?
RMI registry
lookup
register
client
server
stubs skeletons
stubs skeletons
RMI
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RMI can use various directory services. RMI
includes rmiregistry service - the registry
service runs on each machine, which hosts
remote objects and accepts requests for
services - default TCP/IP port 1099 Client
the RMI registry service provides lookup
method specification of required remote object
service URL rmi//lthost_namegt ltname_service
_portgt /ltservice_namegt
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Using RMI Components of an RMI based
application interface definitions for remote
services implementations of remote
services stub and skeleton files server(s) to
host the services RMI naming service client
program optional class file provider Example
remote calculator service and client program
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Step 1 write and compile service interfaces
import java.rmi.Remote import java.rmi.RemoteExce
ption public interface Calculator extends
Remote public long add(long a, long b)
throws RemoteException public long sub(long
a, long b) throws RemoteException public
long mul(long a, long b) throws
RemoteException public long div(long a,
long b) throws RemoteException
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Step 2 write and compile service implementation
import java.rmi.server.UnicastRemoteObject import
java.rmi.RemoteException public class
CalculatorImpl extends UnicastRemoteObject
implements Calculator // Implementations
must have an explicit constructor // in order
to declare the RemoteException exception
public CalculatorImpl() throws RemoteException
super() public long add(long
a, long b) throws RemoteException
return a b public long sub(long a,
long b) throws RemoteException return a
- b public long mul(long a, long b)
throws RemoteException return a b
public long div(long a, long b) throws
RemoteException return a / b
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Step 3 generate stub and skeleton classes RMI
compiler part of JDK rmic CalculatorImpl Res
ult CalculatorImpl_Stub.class CalculatorImpl_
Skel.class
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Step 4 write remote service class
import java.rmi.Naming public class
CalculatorServer public CalculatorServer()
try Calculator c new
CalculatorImpl() Naming.rebind("rmi//local
host1099/CalculatorService", c) catch
(Exception e) System.out.println("Trouble
" e) public static void
main(String args) new CalculatorServer()

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Step 5 write client program
import java.rmi.Naming import java.rmi.RemoteExce
ption import java.net.MalformedURLException impo
rt java.rmi.NotBoundException public class
CalculatorClient public static void
main(String args) try
Calculator c (Calculator)
Naming.lookup("rmi//localhost/CalculatorService")
System.out.println( c.sub(4, 3)
) System.out.println( c.add(4, 5)
) System.out.println( c.mul(3, 6)
) System.out.println( c.div(9, 3)
) catch (MalformedURLException
murle) lt.. some code here ..gt
catch (RemoteException re) lt.. some code here
..gt catch (NotBoundException
nbe) lt.. some code here ..gt
catch (java.lang.ArithmeticException ae) lt..
some code here ..gt
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Remarks on parameter passing in RMI Parameters
in a single JVM primitive types by
value object types object reference by
value Parameters in RMI primitive types by
value object types (of course) by value ?
object serialization local reference to a remote
object reference to the proxy