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RMI

3

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,

2

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RMI

,

,

(remotemethod invocation RMI)

3

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RMI

4

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RMI

5

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RMI

(), ()

,

-, :

6

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RMI

(Retry Request Message):

, ,

(Duplicate Filtering):

, ,

(Retransmission ofResults): history ,

, 7

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Invocation Semantics

Maybe invocation semantics: , , . . , .

At-Least-Once Invocation Semantics: , , . , . (.. ).

At-Most-Once Invocation Semantics: , , . , .

8

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RMI

RMI compiler Stub Proxy

Skeleton

Remote Method Invocation (RMI)

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Client Server

Stub SkeletonNetwork

(marshalling)

(unmarshalling)

server

server

Stubs Skeletons

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interfaces java.rmi RMI compiler

rmic command line compiler JDK

rmic [full class name including packages] :rmic RMITest

:RMITest_Stub

RMITest_Skel

-keep stub skeleton

Java RMI

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To RMI : (remote objects)

by reference (serializable objects)

JVMs

by value

by value

Remote

Serializable

(by value vs. by reference)

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Java RMI

5.16

To Shape remote interface remote ( 2)

GraphicalObject serializable ( 1) 13

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(naming service)

RMIregistry remote

java.rmi.Naming

registry URL-style ://computerName:portNumber/human-readable-objectName

computerName: RMIregistry

portNumber: RMIregistry

human-readable-objectName:

Java RMIregistry

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RMIregistry (Naming class)

15

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Java RMI client

O client ShapeListinterface ( 1)

allShapes(

2) 16

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RMISecurityManager

main client server security manager RMIclient/server

O default security manager RMISecurityManager

,

security manager RMISecurityManager

17

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Policy

..

, , sockets..

, , , , ( )

policy SecurityManager defaultjava.home/lib/security/java.policy

java.net.SocketPermission policy

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Policy

grant {

permission java.security.AllPermission;

};

grant {

// Allow to connect to any port above 1024

permission java.net.SocketPermission "localhost:1024-", "connect, resolve";

// Allow to accept to any port above 1024

permission java.net.SocketPermission "localhost:1024-", "accept, resolve";};

19

-Djava.security.manager -Djava.security.policy = myRMIapp.policy

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Java RMI 1

,

java.rmi.Remote java.rmi.RemoteException

(servant class)

java.rmi.UnicastRemoteObject

20

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Java RMI 2

(server skeleton) () (client stub)

javac

RMI, rmic

21

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Java RMI 3

,

22

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Marshalling/Unmarshalling

( ,)

RMI vs. Sockets

RMI

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Java RMI :Shared Whiteboard

Shared Whiteboard = :, , , ..

24

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server

version number (int) whiteboard

version number server, version

number 25

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Java RMI

To Shape remote interface

remote ( 2)

GraphicalObject serializable ( 1)

26

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GraphicalObject class

: , ,line color, fill color

/

27

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ShapeList

28

import java.rmi.*;import java.rmi.server.UnicastRemoteObject;import java.util.Vector;

public class ShapeListServant extends UnicastRemoteObject implements ShapeList {private Vector theList; // contains the list of Shapes 1private int version;

public ShapeListServant()throws RemoteException{...}public Shape newShape(GraphicalObject g) throws RemoteException { 2

version++;Shape s = new ShapeServant( g, version);theList.addElement(s); 3return s;

}public Vector allShapes()throws RemoteException{...}public int getVersion() throws RemoteException { ... }

}

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Java RMI Server

29

import java.rmi.*;public class ShapeListServer{

public static void main(String args[]){System.setSecurityManager(new RMISecurityManager());

try{ShapeList aShapeList = new ShapeListServant(); 1Naming.rebind("rmi://127.0.0.1/ShapeList", aShapeList ); 2System.out.println("ShapeList server ready");

}catch(Exception e) {System.out.println("ShapeList server main " + e.getMessage());}

}}

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Java RMI client ()

O client ShapeListinterface ( 1)

allShapes( 2)

30

rmi://127.0.0.1/ShapeList

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Java RMI client () client

allShapes(), getAllState() Shapeinterface ,

, newShape() server, GraphicalObject

O version number server ( ) server ,

31

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Java RMI :

add server

32

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Java RMI

import java.rmi.*;

public interface AddServerIntf extends Remote {

double add(double d1, double d2) throws RemoteException;}

33

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remote objectimport java.rmi.*;

import java.rmi.server.*;

public class AddServerImpl extends UnicastRemoteObject implementsAddServerIntf {

public AddServerImpl() throws RemoteException{

}

public double add(double d1, double d2) throws RemoteException

{ return d1 + d2;

}

}

34

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RMI server

35

import java.net.*;

import java.rmi.*;

public class AddServer {

public static void main(String args[]) {

try {AddServerImpl addServerImpl = new AddServerImpl();Naming.rebind("AddServer", addServerImpl);

}

catch(Exception e) { System.out.println("Exception: " + e); }}

}

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RMI clientimport java.rmi.*;

public class AddClient {

public static void main(String args[]) {

try {

String addServerURL = "rmi://" + args[0] + "/AddServer";

AddServerIntf addServerIntf =

(AddServerIntf)Naming.lookup(addServerURL);

System.out.println("The first number is: " + args[1]);double d1 = Double.valueOf(args[1]).doubleValue();

System.out.println("The second number is: " + args[2]);

double d2 = Double.valueOf(args[2]).doubleValue();

System.out.println("The sum is: " + addServerIntf.add(d1, d2));

}

catch(Exception e) {

System.out.println("Exception: " + e);

}

}

} 36

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Compile all aforementioned Java source files and keep

all generated .class files in the same directory. Before you can use the client and the server, you must

generate the necessary stub.

You may also need to generate a skeleton, if a serverruns on a machine that does not have Java 2, but hasan earlier version of JVM.

1. Generate stubs and skeletons (deprecated!)

To generate stubs and skeletons, you use the RMIcompiler: rmic AddServerImpl

This command generates two new files:AddServerImpl_Skel.class (skeleton) and

AddServerImpl_Stub.class (stub). 37

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2. Start the RMI registry

Go to the directory on the server machine where youkeep files mentioned above.

If your server is on another Windows machine: startrmiregistry

If your server is on a UNIX machine: rmiregistry &

3. Start the server

In the same directory: java AddServer

4. Run the client

j AddCli 6