remotemathimpl.java

this gives details of the network programming

// Implementation of RemoteMath interface for RMI server
// This class implements the interface RemoteMath which is used to support 
// RMI based simple math operations. This class extends
// UnicastRemoteObject (this is the simplest way to create a class
// that will become available as a remote object). See the example
// named AlternativeSimpleRMI for another approach...

import java.net.*;    // need this for MalformedURLException
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

// Note that this class will be used to
// generate stub and skeleton files ... (using rmic)
//
// In this example we include a main, in general you would probably not
// include a main() in the remote object class definitions...

public class RemoteMathImpl extends UnicastRemoteObject implements RemoteMath {

    // We need to create a constructor (even if it does nothing).
    // The constructor must throw RemoteException - since 
    //    when a new UnicastRemoteObject is created it requires some
    //    communication resources that may not be available!
    // In this constructor we just call the constructor for
    // UnicastRemoteObject which exports the object 

    public RemoteMathImpl() throws RemoteException {
	super();
    }

    // For this simple example we include a main here, in general
    // we will define remote objects and create them elsewhere
    // (in general we don't put main inside the implementation
    // of a remote object).

    public static void main(String args[]) { 
	try {
	    // create a RemoteMathImpl object 
	    RemoteMathImpl r = new RemoteMathImpl();

	    // register the object with the rmi registry
	    // (registry mush already be running)
	    Naming.rebind("ReMath",r);
	    System.out.println("Registered RemoteMath object\n"); 

	} catch (RemoteException e) {
	    System.out.println("RemoteException: " + e.getMessage());
	    e.printStackTrace();

	} catch (MalformedURLException m) {
	    System.out.println("URL Problem: " + m.getMessage());
	    m.printStackTrace();
	}
    }

    // Below are the actual remote methods. Although these are
    // simple methods in this example - it's worth noting that aside
    // from the declaration that each can throw RemoteException, there
    // is no difference between the code in these methods and in
    // a local method (the fact that these methods can be called
    // remotely doesn't change the way we write the code.

    // LogRequest is just doing some printing here, although in a real
    // service you might want to replace this with code that does
    // something fancy (actually log to a file or to syslog).

    public int Add(int x, int y) throws RemoteException {
	LogRequest("ADD: " + x + "+" + y);
	return(x+y);
    }
    public int Sub(int x, int y) throws RemoteException {
	LogRequest("SUB: " + x + "-" + y);
	return(x-y);
    }
    public int Mult(int x, int y) throws RemoteException {
	LogRequest("MULT: " + x + "*" + y);
	return(x*y);
    }
    public int Div(int x, int y) throws RemoteException {
	LogRequest("DIV: " + x + "/" + y);
	return(x/y);
    }

    void LogRequest(String s) {
	System.out.println("RemoteMath Request: " + s );
    }

}