This document discusses Java Remote Method Invocation (RMI), which allows Java objects to invoke methods on other Java objects running in another Java Virtual Machine (JVM). It describes how RMI works using a client-server model, with an interface defining remote methods, an implementation class on the server exporting objects, and clients looking them up by name. It provides code examples of an RMI server interface, implementation class, and client class, along with steps for compiling, running the rmiregistry, and potential error sources.

1. By
Om Nishant
080911216

2. Java remote method invocation
 The Java Remote Method Invocation Application
Programming Interface (API), or Java RMI, is a Java
application programming interface that performs the
object-oriented equivalent of remote procedure calls
(RPC).
 Typically comprise 2 separate programs:-
 Client
 Server
 A remote interface specifies the methods that can be
invoked remotely by a client

3. RMI Server Interface
import java.rmi.Remote;
import java.rmi.RemoteException;
/*interface must extend Remote to enable access from
another JVM
The methods being remote methods can throw Remote
Exception */
public interface RmiServerIntf extends Remote {
public String getMessage() throws RemoteException;
/*This is the method implemented by server and
accessed by client*/
}

4. Implementing the interface
 An RMI server program needs to create the initial
remote objects and export them to the RMI runtime
 The setup procedure should do the following:
 Create and install a security manager
 Create and export one or more remote objects
 Register at least one remote object with the RMI
registry (or with another naming service

5. RMI Server Program
import java.rmi.Naming;
import java.rmi.registry.*;
import java.rmi.RemoteException;
import java.rmi.RMISecurityManager;
import java.rmi.server.UnicastRemoteObject;
//public class classname implements remote-interface
public class RmiServer extends UnicastRemoteObject implements RmiServerIntf {
public static final String MESSAGE = "Hello world";
public RmiServer() throws RemoteException {
//constructor defn }
public String getMessage() {
//Todo code for the remote method(s)
return MESSAGE;
}

6. public static void main(String args[]) {
//main method is used to create an instance and make it available to clients.
//Write the todo code here
System.out.println("RMI server started");
// Create and install a security manager
if (System.getSecurityManager() == null) {
System.setSecurityManager(new RMISecurityManager());
System.out.println("Security manager installed.");
} else {
System.out.println("Security manager already exists.");
}

7. try {
//special exception handler for registry creation
//Registry used for naming services
LocateRegistry.createRegistry(1099);
System.out.println("java RMI registry created.");
}
catch (RemoteException e) {
//do nothing, error means registry already exists
System.out.println("java RMI registry already exists.");
}

8. try {
//Instantiate RmiServer
//(ClassNAme)UnicastRemoteObject.exportObject(object1, portno);
RmiServer obj = new RmiServer();
// Bind this object instance to the name "RmiServer“
Naming.rebind("//localhost/RmiServer", obj);
System.out.println("PeerServer bound in registry");
}
catch (Exception e) {
System.err.println("RMI server exception:" + e);
e.printStackTrace();
}
}
}

9. import java.rmi.Naming;
import java.rmi.RemoteException;
import java.rmi.RMISecurityManager;
public class RmiClient {
// "obj" is the reference of the remote object
RmiServerIntf obj = null;
public String getMessage() {
try {
obj = (RmiServerIntf)Naming.lookup("//localhost/RmiServer");
return obj.getMessage();
} catch (Exception e) {
System.err.println("RmiClient exception: " + e);
return e.getMessage();
}
}

10. public static void main(String args[]) {
// Create and install a security manager
if (System.getSecurityManager() == null) {
System.setSecurityManager(new RMISecurityManager());
}
RmiClient cli = new RmiClient();
System.out.println(cli.getMessage());
}
}

11. Implementation:
 Compile the source code files
 javac filename
 Create the stub for client and skeleton for server
 rmic serverfilename
 Start the server
 rmiregistry
 Ensure security permits are in order
 Run the server and client files

12. Common sources of errors
 Before running the server, make sure you have an
instance of rmiregistry running on the server
 Make sure that your CLASSPATH variable is empty
 Not having a suitable security policy
 Mixing Java versions