RMI Components

• java.rmi: client-side RMI classes, interfaces, and exceptions

• java.rmi.server: server-side RMI classes, interfaces, and exceptions

• java.rmi.registry: Classes for naming services

• java.rmi.dgc: distribute garbage collection

• java.rmi.activation: Implements activate on demand RMI services. Objects instantiated on-demand by client-requests. References persistent over server crashes.

• rmic: compiler to generate stubs and skeletons• rmiregistry: Utility server that provides

naming service for RMI. Associates names with objects

• rmid: utility server to RMI activation framework

RMI Server Properties

• java.rmi.server.codebase: a url indicating code base from which classes should be loaded to network clients

• java.rmi.server.disableHttp: if true, RMI will not use Http to try to tunnel through firewalls. Default is false, meaning that Http wraps RMI calls

• java.rmi.server.hostname: sets servers fully qualified host name, if name unavailable via DNS

• java.rmi.server.logCalls: if true, RMI will log information about calls. Default is false.

• java.rmi.dgc.leaseValue: The time in milliseconds until server notices client is no longer connected. Default is 10 minutes.

RMI Naming Methods

• Remote lookup(String name): Look up remote object by URL and return it

• bind(String name, Remote obj): bind an object to a specific URL

• unbind(String name): unbind an object at a URL

• rebind(String name, Remote obj): Replace the object currently bound with a new one

• String[] list(String name): list of URL’s from specified Registry

Creating RMI Application

• Create and compile remote object interface that extends java.rmi.Remote

• Implement a server application that contains a remote object class that implements your interface

• Compile the server application and run rmic to generate stubs classes.

• Install the class files in a known location, such as web root directory. RMI by default uses web server to for sharing classes.

• Run rmiregistry on the server machine so it can manage remote objects

• Run the server application and have it install an instance of the remote object with a unique name in the registry.

• Implement a client application that connects to the server and looks up the remote object by name in a remote object registry.

• Compile, then Run client

package message;

import java.rmi.Remote;import java.rmi.RemoteException;

public interface MessageServer extends Remote{

static String SERVER_NAME = "Message_Server";

void send(String name, String s) throws RemoteException;}

package server;

import java.rmi.*;import java.rmi.server.*;import java.rmi.registry.*;import message.*;

public class Server extends UnicastRemoteObject implements MessageServer{ public Server() throws RemoteException

{ super(); }

public void send(String name, String s) throws RemoteException{

System.out.println(name + ": " + s); }

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

try { MessageServer srv = new Server();

// Bind server to local registry on default port Naming.rebind(MessageServer.SERVER_NAME, srv);

System.out.println("Server bound and started"); } catch (Exception e) { System.err.println("Server exception: " + e.getMessage()); e.printStackTrace(); } }}

package client;

import java.io.*;import java.rmi.*;import java.rmi.server.*;import message.*;

public class Client{

static String name; // name of this client static MessageServer server; //Connection to the server

public static void main(String args[]){

if(args.length<1){

System.out.println("Usage: java client.Client ClientName");System.exit(-1);

}

name = args[0];

System.setSecurityManager(new RMISecurityManager());

try{

server =(MessageServer)Naming.lookup(MessageServer.SERVER_NAME);

//Now, loop and process input from the user untilthey type 'exit'

boolean notDone = true;String message = null;BufferedReader br = new BufferedReader(new

InputStreamReader(System.in));

System.out.println("Type 'exit' to end.");

while(notDone){

System.out.print("Enter message:"); message = br.readLine();

if(message.startsWith("exit")) notDone=false;else server.send(name,message);

} } catch (Exception e)

{ System.err.println("Client exception: " + e.getMessage()); e.printStackTrace();

System.exit(-1); } }}

grant{

permission java.net.SocketPermission "*:1024-65535", "connect,accept";permission java.lang.RuntimePermission "setSecurityManager";permission java.lang.RuntimePermission "createSecurityManager";

};

javac message\*.java

javac server\*.javarmic -d . server.Server

javac client\*.java

REM Start local registrystart rmiregistry

REM start java server.Serverstart java -Djava.security.policy=server.policy server.Server

REM give the server a chance to startpause

REM start a few clientsstart java -Djava.security.policy=server.policy client.Client Client1start java -Djava.security.policy=server.policy client.Client Client2start java -Djava.security.policy=server.policy client.Client Client3

package examples.hello;public interface Hello extends java.rmi.Remote {

String sayHello() throws java.rmi.RemoteException;}

package examples.hello;

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

public class HelloImpl extends UnicastRemoteObject implements Hello {private String name;

public HelloImpl(String s) throws RemoteException {super();name = s;

}

public String sayHello() throws RemoteException {return "Hello World!";

}

public static void main(String args[]){

System.setSecurityManager(new RMISecurityManager());

try {HelloImpl obj = new HelloImpl("HelloServer");Naming.rebind("//myhost/HelloServer",obj);System.out.println("HelloServer bound in registry");

} catch (Exception e) {System.out.println("HelloImpl err: " +e.getMessage());e.printStackTrace();

}}

}

package examples.hello;

import java.awt.*;import java.rmi.*;

public class HelloApplet extends java.applet.Applet {String message = "";public void init() {

try {Hello obj = (Hello)Naming.lookup("//" +

getCodeBase().getHost() + "/HelloServer");message = obj.sayHello();

} catch (Exception e) {System.out.println("HelloApplet exception: " +e.getMessage());e.printStackTrace();

}}public void paint(Graphics g) {

g.drawString(message, 25, 50);}

}