How To Add Two Numbers Using RMI

how to add two numbers using RMI..This very simple example is taken from Chapter 24 of "Java 2: The Complete Reference" by P.Naughton and H.Schildt.The example is overly simplified but it still illustrates the basic steps in creating an RMI distributed program.

This example provides step-by-step directions for building a client/server application by using RMI. The server receives a request from a client, processes it, and returns a result. In this example, the request specifies two numbers, the server adds these together and returns the sum.(Of course, this program is intended only to illustrate the basic RMI mechanism.)The next subsections provide main steps in writing an RMI program

Define an interface that declares remote methods.The first file AddServerIntf.java defines the remote interface: it includes one method that accepts two double arguemnts and returns their sum. All remote interfaces must extend the interface Remote, that defines no methods: its purpose is simply to indicate that an interface uses remote methods.All remote methods should throw a RemoteException

import java.rmi.*;
public interface AddServerIntf extends Remote {
double add(double d1, double d2) throws RemoteException;
}
Implement the remote interface and the server

The second source file AddServerImpl.java implements the remote interface:

import java.rmi.*;
import java.rmi.server.*;
public class AddServerImpl extends UnicastRemoteObject
implements AddServerIntf {
public AddServerImpl() throws RemoteException {
}
public double add(double d1, double d2) throws RemoteException {
return d1 + d2;
}
}

All remote objects must extend UnicastRemoteObject which provide the functionaly that is needed to make objects available from remote machines. The third source file AddServer.java contains the main program for the server machine. Its primary function is to update the RMI registry on that machine. This is done by using the rebind() method of the Naming class (it is in java.rmi API). That method associates a name with an object reference.

import java.net.*;
import java.rmi.*;
public class AddServer {
public static void main(String args[]) {
try {
AddServerImpl addServerImpl = new AddServerImpl();

[code]....

Develop a client (an application or an applet) that uses the remote interface..The fourth source file AddClient.java implements the client side of this distributed application. This program requires 3 command line arguments: the IP address or name of the remote server, and two numbers that are to be summed.

The application forms an URL string using the rmi protocol, the first command line argument and the name "AddServer" that is used by naming registry of the server. The the program calls the method lookup() of the Naming class to find a reference to a remote object. All remote method invocations can then be directed to this object.The client program illustrates the remote call by using the method add(d1,d2) that will be invoked on the remote server machine from the local client machine where the client runs.

import java.rmi.*;
public class AddClient {
public static void main(String args[]) {
try {
String addServerURL = "rmi://" + args[0] + "/AddServer";
AddServerIntf addServerIntf =

[code]...

If you do not have an Internet connection, you can run all programs of this example on your local machine (both server and client). In this case, you can run

java AddClient 127.0.0.1 567 999

to use the "loop back" address (127.0.0.1) for the local machine. This will allow you to test the entire RMI mechanism without actually having to install the server on a remote computer.