14th August 1997

VirtualNet (over RMI)

RMI example

Creating the server

The remote version of Virtual Net just need a RMI server; there are no special requirements of Virtual Net on the server.

For this example, the server is going to give only one service: it returns a phone number, those used for its initialization.

The code for this interface is:

public interface PhoneNumbersIntf extends java.rmi.Remote
{
 public String getNumber() throws java.rmi.RemoteException;
}

The code for the server is:

public class PhoneNumbersServer extends java.rmi.server.UnicastRemoteObject 
  implements PhoneNumbersIntf
{
 public PhoneNumbersServer(String number)  throws java.rmi.RemoteException
 {
  Number=number;
 }
 public String getNumber() throws java.rmi.RemoteException
 {
  return Number;
 }
 String Number;
}

Generating servers

The following is the code that generates several servers:

import java.rmi.Naming;
          
import vnet.remote.Host;
          
public class InsertServers
{
 public static void main(String args[])
 {
  try
  {
   System.out.println("This test expects to have a virtualNet called "
    +"TestA, with 4 nodes C,M,U,Y, with links between C-M, M-U, V-Y");
   System.out.println();
   System.out.println("Getting the hosts...");
   Host C=(Host) Naming.lookup("/TestA/HostC");
   Host M=(Host) Naming.lookup("/TestA/HostM");
   Host U=(Host) Naming.lookup("/TestA/HostU");
   Host Y=(Host) Naming.lookup("/TestA/HostY");
   System.out.println("Binding the servers");
   System.out.println("In M there is a server called LMP");
   M.bind("LMP",new PhoneNumbersServer("763271"));
   System.out.println("In Y there is the same server ,but with a "+
    "different number");
   Y.bind("LMP",new PhoneNumbersServer("859829"));
   System.out.println("In C there is a server, hosted in U, called "+
    "BELLMP (/TestA/HostC/BELLMP");
   U.bind("/TestA/HostC/BELLMP", new PhoneNumbersServer("213207"));
   System.out.println();
   System.out.println();
   System.out.println("Ready");
  }
  catch(Exception ex)
  {
   System.out.println(ex);
  }
 }
}

Generating clients

The following is a very small apllication that acts as a client for the previous generated clients.

import java.rmi.Naming;
          
import vnet.remote.Host;
          
public class CheckServers
{
 public static void main(String args[])
 {
  System.out.println("This test expects to have a virtualNet called TestA, with " +
    " 4 nodes C,M,U,Y, with links between C-M, M-U, V-Y");
  if (args.length!=1)
   System.out.println("This test need an argument: The letter of the host from "+
    "where the tests are done");
  else 
   try
   {
    System.out.println("Getting the host");
    Host host=(Host) Naming.lookup("/TestA/Host"+args[0]);
    PhoneNumbersIntf phone=null;
    System.out.println("getting LMP");
    phone=(PhoneNumbersIntf)host.lookup("LMP");
    System.out.println("phone: "+phone.getNumber());
    System.out.println("getting /TestA/HostY/LMP");
    phone=(PhoneNumbersIntf)host.lookup("/TestA/HostY/LMP");
    System.out.println("phone: "+phone.getNumber());
    System.out.println("getting /TestA/HostM/LMP");
    phone=(PhoneNumbersIntf)host.lookup("/TestA/HostM/LMP");
    System.out.println("phone: "+phone.getNumber());
    System.out.println("getting BELLMP");
    phone=(PhoneNumbersIntf)host.lookup("BELLMP");
    System.out.println("phone: "+phone.getNumber());
    System.out.println("getting /TestA/HostC/BELLMP");
    phone=(PhoneNumbersIntf)host.lookup("/TestA/HostC/BELLMP");
    System.out.println("phone: "+phone.getNumber());
    System.out.println("getting /TestA/HostU/BELLMP");
    phone=(PhoneNumbersIntf)host.lookup("/TestA/HostU/BELLMP");
    System.out.println("phone: "+phone.getNumber());
   }
   catch(Exception ex)
   {
    System.out.println(ex);
   }
 }
}

Executing the application

In the RMI remote case, there are four parts:

  • The RMI system
  • The Virtual Net application
  • One or more servers
  • One or more clients

First one has to compile the java files:

javac PhoneNumbersIntf.java
javac PhoneNumbersServer.java
javac InsertServers.java
javac CheckServers.java

It you get any compiler error, probably the classpath has not been properly set. In this case, go to the page on Availability to know how to set it. Then, we start the RMI registry:

start rmiregistry (rmiregistry & in Unix)

Now, we need to have the Virtual Net application, and to initialize a net called TestA that will be used by the servers and clients.

There are several ways to execute this application. One of them is generating another program that creates an object vnet.remote.VirtualNet.

Another way is to use one of the two programs hosted in vnet.remote.prg. We will use the graphic version:

javaw vnet.remote.prg.GraphMain -init=+C+M+U+Y+MU1+MC2+MY3 -start TestA

The graph of this net is:

Before executing the server or client applications, you have to generate the stub for the server, and its stub and skeleton:

rmic PhoneNumbersServer
java vnet.remote.vnc PhoneNumbersServer
javac PhoneNumbersServer_Stub_VNet.java
rmic PhoneNumbersServer_Stub_VNet

Now, it is already possible to install the servers:

java InsertServers

The output of this program will be:

This test expects to have a virtualNet called TestA, with 4 nodes C,M,U,Y, with
links between C-M, M-U, V-Y
          
Getting the hosts...
Binding the servers
In M there is a server called 
In Y there is the same server ,but with a different number
In C there is a server, hosted in U, called BELLMP (/TestA/HostC/BELLMP
          
Ready

Finally, we test the client:

java CheckServers C

The ouput is:

This test expects to have a virtualNet called TestA, with 4 nodes C,M,U,Y, with
links between C-M, M-U, V-Y
Getting the host
getting LMP
phone: 763271
getting /TestA/HostY/LMP
phone: 859829
getting /TestA/HostM/LMP
phone: 763271
getting BELLMP
phone: 213207
getting /TestA/HostC/BELLMP
phone: 213207
getting /TestA/HostU/BELLMP
java.rmi.NotBoundException: /TestA/HostU/BELLMP

Download the example

vnetexrmi.zip (10 KB)

Once unzipped this file -and having correctly set the classpath-, to execute the example is just needed to do:

start rmiregistry (rmiregistry & in Unix)
javaw vnet.remote.prg.GraphMain -init=+C+M+U+Y+MU1+MC2+MY3 -start TestA
start java InsertServers (java InsertServers & in Unix)
java CheckServers C