Java remote method invocation

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

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*/ }

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

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; }

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."); }

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."); }

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(); } } }

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(); } }

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()); } }

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

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

Java remote method invocation

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