java RMI

Making the Remote Service
Step one: Make a Remote interface

Remote interface should extend java.rmi.Remote interface

Declare that all methods throw a RemoteException as every remote call is considered risky

Arguments and return values of remote methods must be either primitive or serializable(Strings, arrays, collections etc), if passing self defined types be sure to implement serializable interface to the class.

Step two: Make a Remote Implementation

Implement the Remote interface created earlier.

Extend java.rmi.server.UnicastRemoteObject to the class

As the super class UnicastRemoteObject's constructor throws a Remote Exception it is necessary to write a no-arg constructor that declares a Remote exception in our class.

To make available the remote service to clients register the service with RMI registry

Step three: Generate Stubs

Compile java files

Runrmic on the remote implementation class. To do this use the following command: rmic MyRemoteImplementation. This will create MyRemoteImplementation_Stub.class which is going to be the client helper.

Step four: run rmiregistry

Open a new terminal and goto the directory where your class files reside using command cd

Start rmiregistry using following command: rmiregistry

Step five: Start the service

open a new terminal and run the service following way: java MyRemoteImplementation

Server Code
Remote interface

import java.rmi.*;
public interface MyRemoteInterface extends Remote{ //step 1.1 
public int doCalc(int a,int b) throws RemoteException; //step 1.2 & step 1.3
}

Remote service

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

public class MyRemoteImplementation extends UnicastRemoteObject implements MyRemoteInterface {//step 2.1 & 2.2
 
 public MyRemoteImplementation() throws RemoteException {} //step 2.3

 public int doCalc(int a,int b){  
  int result=a+b;
  System.out.println("Returned the result= "+result+" to client!");
  return result;
 }
 
 public static void main(String args[]){
  
  MyRemoteInterface service=null;
  try {
   service = new MyRemoteImplementation();
  } catch (RemoteException e) {
   e.printStackTrace();
  }
  try {
   Naming.rebind("welcome", service); //step 2.4 and be sure to give a name without spaces
  } catch (RemoteException e) {
   e.printStackTrace();
  } catch (MalformedURLException e) {
   e.printStackTrace();
  }
  
 }
}

Note: Server should have following three classes to work.

MyRemoteInterface.class

MyRemoteImplementation.class

MyRemoteImplementation_Stub.class

How client works?
Note: Client should have following three classes to work.

MyRemoteInterface.class

MyRemoteClient.class

MyRemoteImplementation_Stub.class

Client does a lookup on the RMI registry and RMI registry returns the stub object. Stub pretends to be the real service and let client invokes the method in it.
Client Code

import java.rmi.*;

public class MyRemoteClient {
 
 public static void main(String args[]){
  
  new MyRemoteClient().getResult();
  
 }
 
 public void getResult(){
  
try{
   
   MyRemoteInterface service=(MyRemoteInterface)Naming.lookup("rmi://127.0.0.1/welcome");//Client does 
//the lookup on the RMI registry
   int result=service.doCalc(1,2);
   System.out.println("hello I got the result "+result);
   
   }catch(Exception e){
    e.printStackTrace();
   }
  
 }


}

Output