Java RMI

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Java RMI

• Stanislav Chachkov
• LGL-EPFL

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What is RMI?

• RMI enables the programmer to create distributed
  Java applications, in which the methods of remote
  Java objects can be invoked from other Java
  virtual machines, possibly on different hosts.
• A Java program can make a call on a remote object
  once it obtains a reference to the remote object,
  either by looking up the remote object in the
  naming service provided by RMI or by receiving
  the reference as an argument or a return value. A
  client can call a remote object in a server, and
  that server can also be a client of other remote
  objects.
• RMI uses object serialization to marshal and
  unmarshal parameters.

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What is RMI?

• Remote Method Invocation

network
Object Client
Remote Object Server
method invocation
Host tata.epfl.ch
Host titi.epfl.ch
4
NetBank example
Client
Bank Office
BankMgr
Account
Host ecub.ubs.ch
Host serv.ubs.ch
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Creating a Remote object
interface java.rmi.Remote
java.rmi.server. UnicastRemoteObject
bank.BankMgrImpl
interface bank.BankMgr
createClient() createAccount(Client)
bank.BankMgrImpl_Stub
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Remote Reference

• Encapsulates network communication
• Same interface as Remote object

Object Client
Remote Object Stub
Remote Object
RMI Runtime
01101
f()
f()
true
10010
true
Host tata.epfl.ch
Host titi.epfl.ch
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Naming Service

• Directory that associates names to remote objects
  (bind)

Remote Object A
Naming
Remote Object C
X
Y
Remote Object B
Z
Host titi.epfl.ch
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Naming Service

• Client use Naming Service to find a particular
  Server object (lookup)

Naming
Object Client
Remote Object Server
X
lookup(Y)
Y
Remote ref. to Server
Z
tata.epfl.ch
Host titi.epfl.ch
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Creating Remote object

• Create an interface
• Create the implementation
• Compile
• Create the Stub

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Interface

• public interface BankMgr extends Remote
• public createAccount(Client c)
• throws RemoteException
• public createClient(String name)
• throws RemoteException

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Implementation class

• public class BankMgrImpl
• extends UnicastRemoteObject
• implements BankMgr
• public BankMgrImpl()
• throws RemoteExceptionsuper()
• public createClient(String a) code
• public createAccount(Client b) code

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Stub

• In JBuilder use JNI/RMI tab in class properties
  to generate it automatically
• By hand use rmic tool
• rmic bank.BankMgrImpl

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Binding (server side)

• Binding means register the object in local
  Naming service
• Naming.rebind(
• LGLBank,
• new BankMgrImpl())

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Locating (client side)

• Lookup operation return the reference (stub) on a
  remote object
• BankMgr bank
• (BankMgr)Naming.lookup(
• //titi.epfl.ch/LGLBank)

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Parameters and Return Values

• Remote objects by reference
• Serializable objects - by copy
• Others cannot be passed (exception)

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Deployment

• On the server host
• Launch Naming service
• rmiregistry
• Launch Server program
• java bank.BankMgr
• On the client host(s)
• Launch the client program

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References

• Java Tutorial on RMI
• http//java.sun.com/j2se/1.4/docs/guide/rmi
• Book on RMI
• William Grosso Java RMI, OReilly