What and How is RMI ??

What is RMI

Enables the programmer to create distributed applications (Java-Java), in which the methods of
remote Java objects can be invoked from other Java virtual machines, possibly on different hosts.

RMI uses object serialization to marshal and unmarshal parameters and does not truncate types, supporting true object-oriented polymorphism

Architecture

Advantages

Object Oriented

Mobile Behavior

Design Patterns

Safe and Secure

Easy to Write/Easy to Use

Connects to Existing/Legacy Systems

Write Once, Run Anywhere

How to implement RMI ?

Write and compile Java code for interfaces

Write and compile Java code for implementation classes

Generate Stub and Skeleton class files from the implementation classes

Write Java code for a remote service host program

Develop Java code for RMI client program

Install and run RMI system

Note: while declaring & implementing methods they should throws RemoteException

How to run a sample program ?

Interface


import java.lang.*;

import java.rmi.*;

public interface Hello extends java.rmi.Remote {

public String sayHellow() throws java.rmi.RemoteException;

}

Implementation Class:

import java.rmi.*;

import java.rmi.server.*;

class HelloImpl extends UnicastRemoteObject implements Hello {
HelloImpl () throws java.rmi.RemoteException { }
public String sayHellow() throws java.rmi.RemoteException

{

System.out.println(“In say Hello ");

return” Hello! Welcome to the world of RMI”;

}

}

Creating the Server

import java.util.*;

import java.rmi.*;

import java.rmi.RMISecurityManager;

public class HelloServer

{

public static void main( String args[] )

{

System.setSecurityManager( new RMISecurityManager());

try {

System.out.println ("Starting Hello Server");

HelloImpl hello =new HelloImpl ();

System.out.println ("Binding Server");

Naming. rebind (“hello", hello );

System. out. print ("Server is waiting");

}

catch( Exception e )

{

System. out. print ("An error occured");

e. printStackTrace ();

System.out.println(e.getMessage());

}

} }

Creating the Client


import java.util.*;

import java.net.*;

import java.rmi.*;

import java.rmi.RMISecurityManager;

public class HelloClient {

public static void main( String args[] ) {

System.setSecurityManager( new RMISecurityManager());

try {

System.out.println("Starting calcClient");

String url = new String( “rmi://"+ args[0] + "/hello");

System.out.println(“Hello Server Lookup: url =" + url);

hello = (Hello)Naming.lookup( url );

if(hello != null )

{ System.out.println(hello.sayHello());//invoking remote method

} else {

System.out.println("Requested Remote object is null.");

}

} catch( Exception e ) {

System.out.println("An error occurred");

e.printStackTrace();

System.out.println(e.getMessage());

}

}

}




Running the Client and the Server

Start the rmi registry

start rmiregistry

Compile all classes

Create stubs & skeletons

rmic HelloImpl

Start the server

java HelloServer

Start the Client

java HelloClient localhost

Sample program architecture