RMI 003

[Javini Javono]

Hi,
This is a follow-up question, based upon this link here at this site:
http://www.coderanch.com/t/184995/java-developer-SCJD/certification/RMI
The next question to consider, or the next observation to be made, is
that our ...Impl method no longer need declare the, perhaps, troublesome
remote exception in every method anymore.
So, here is package rmi3, with the contents of the GenImpl class,
but this time I've commented out every exception thrown. This
compiles and runs without error. The complete rmi3 package
runs against either localhost or against a live internet connect.
Also, this ...Impl class (GenImpl) does not extend UnicastRemoteObject.

package rmi3;
import java.io.*;
import java.rmi.*;
import java.rmi.server.*;
public class GenImpl extends Object implements GenRemoteInterface, Serializable {

private Stringname;

public GenImpl(String name) /* throws RemoteException */ {
this.name = name;
}

//  Whether this is called or not, makes no difference.

public void rmiExport(int port) /* throws RemoteException */ {
try {
//The second argument of 0 means that any suitable
//port can be used to listen to client connections.

UnicastRemoteObject.exportObject(this, port);
} catch (Exception tried) {
tried.printStackTrace();
}
}

public String getDescription() /* throws RemoteException */ {
return "I am a " + name + ";  feed me!";
}

/*
Removes the remote object, obj, from the RMI runtime.
This method has not been tested yet.
*/

void disposeOfAllResources(boolean force) /* throws RemoteException */ {

try {
UnicastRemoteObject.unexportObject(this, force);
} catch (Exception tried) {
tried.printStackTrace();
}
}
}

So, now we have added two possible components of flexibility which
perhaps can be leveraged to our advantage:
1. GenImpl no longer has to extend UnicastRemoteObject, but
can extend one of our own, and
2. GenImpl's methods need not declare any exceptions, such as
RemoteException, but only those that we specifically decide it will throw, if any.
To test the exception capability, I told my Mac to be a web server, and I
received an on-the-fly http://there.somewhere.com/ URL, wherein, when
I go to it, it is my computer; that is, this is, I think, exercising the
internet (for when I run the client, the modem indicator lights up
as if it is being used).
After testing out package rmi3, I then shut down the GenServer
application. Then I ran the client GenClient; surely, something bad should
occur, and here is the error I received:

$ java rmi3/GenClient
GenClient.main():  Application started.
[B]java.rmi.ConnectException:[/B] Connection refused to host: there.somewhere.com; nested exception is: 
        java.net.ConnectException: Connection refused
        at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:567)
        at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:185)
        at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:171)
        at sun.rmi.server.UnicastRef.newCall(UnicastRef.java:313)
        at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
        at java.rmi.Naming.lookup(Naming.java:84)
        at rmi3.GenClient.main(GenClient.java:24)
Caused by: java.net.ConnectException: Connection refused
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:305)
        at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:171)
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:158)
        at java.net.Socket.connect(Socket.java:426)
        at java.net.Socket.connect(Socket.java:376)
        at java.net.Socket.<init>(Socket.java:291)
        at java.net.Socket.<init>(Socket.java:119)
        at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:22)
        at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:128)
        at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:562)
        ... 6 more
GenClient.main():  This application has exited.
$ 

And the exception I received, java.rmi.ConnectException, is a direct
sub-class of RemoteException:

java.rmi 
Class ConnectException
java.lang.Object
  java.lang.Throwable
      java.lang.Exception
          java.io.IOException
              java.rmi.RemoteException
                  java.rmi.ConnectException

and as seen just above, ConnectException is a direct sub-class of RemoteException.
And, I received this exception without having to declare each method
has throwing a RemoteException and without having to declare
the class as having extended UnicastRemoteObject.
As I am just learning this stuff, if anyone has added-value comments
on these new experiences in Java, they would be much appreciated.
Thanks,
Javini Javono
[ January 25, 2004: Message edited by: Javini Javono ]