Download CSCE 790: Computer Network Security

CSCE 515:
Computer Network Programming
Chin-Tser Huang
[email protected]
University of South Carolina
An RMI Chat with Callback Example




An RMI-based client/server chat system with callback
mechanism
Define remote interfaces RMICallbackServer and
RMICallbackClient
Server class RMICallbackServerImpl accepts client
registration through interface RMICallbackServer
Client class RMICallbackClientImpl sends messages to
server and server broadcasts messages to each
registered client through interface RMICallbackClient
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2
Interface RMICallbackServer
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.rmi.*;
public interface RMICallbackServer extends Remote {
public static final String REGISTRY_NAME = "Callback Server";
public abstract void register (RMICallbackClient client) throws RemoteException;
public abstract void deregister (RMICallbackClient client) throws RemoteException;
public abstract void say (String message) throws RemoteException;
}
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Interface RMICallbackClient
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.rmi.*;
public interface RMICallbackClient extends Remote {
public abstract void said (String message) throws RemoteException;
}
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Class RMICallbackServerImpl
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import
import
import
import
java.rmi.*;
java.util.*;
java.rmi.server.*;
java.rmi.registry.*;
public class RMICallbackServerImpl extends UnicastRemoteObject
implements RMICallbackServer {
// public RMICallbackServerImpl () throws RemoteException …
// public void register (RMICallbackClient client) …
// public void deregister (RMICallbackClient client) …
// public void say (String message) …
// public static void main (String[] args) throws RemoteException …
}
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Methods of RMICallbackServerImpl
protected Vector clients;
public RMIChatServerImpl () throws RemoteException {
clients = new Vector ();
}
public void register (RMICallbackClient client) {
try {
say (getClientHost () + " has joined.");
} catch (ServerNotActiveException ignored) {
}
clients.addElement (client);
}
public void deregister (RMICallbackClient client) {
clients.removeElement (client);
try {
say (getClientHost () + " has left.");
} catch (ServerNotActiveException ignored) {
}
}
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Method say
public void say (String message) {
Vector clients = (Vector) this.clients.clone ();
for (int i = 0; i < clients.size (); ++ i) {
RMICallbackClient client = (RMICallbackClient) clients.elementAt (i);
try {
client.said (message);
} catch (RemoteException ex) {
this.clients.removeElement (client);
}
}
}
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Method main
public static void main (String[] args) throws RemoteException {
RMICallbackServerImpl callbackServer = new RMICallbackServerImpl ();
Registry registry = LocateRegistry.getRegistry ();
registry.rebind (REGISTRY_NAME, callbackServer);
}
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Class RMICallbackClientImpl
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import
import
import
import
import
java.awt.*;
java.rmi.*;
java.awt.event.*;
java.rmi.server.*;
java.rmi.registry.*;
public class RMICallbackClientImpl extends UnicastRemoteObject implements RMICallbackClient, ActionListener{
// public RMICallbackClientImpl (String host) throws RemoteException …
// public synchronized void start () throws RemoteException, NotBoundException …
// public synchronized void stop () throws RemoteException …
// public void said (String message) …
// public void actionPerformed (ActionEvent ev) …
// public static void main (String[] args) throws RemoteException, NotBoundException …
}
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Constructor RMICallbackClientImpl
protected
protected
protected
protected
String host;
Frame frame;
TextField input;
TextArea output;
public RMICallbackClientImpl (String host) throws RemoteException {
this.host = host;
frame = new Frame ("RMICallbackClientImpl [" + host + "]");
frame.add (output = new TextArea (), "Center");
output.setEditable (false);
frame.add (input = new TextField (), "South");
input.addActionListener (this);
frame.addWindowListener (new WindowAdapter () {
public void windowOpened (WindowEvent ev) {
input.requestFocus ();
}
public void windowClosing (WindowEvent ev) {
try {
stop ();
} catch (RemoteException ex) {
ex.printStackTrace ();
}
}
});
frame.pack ();
}
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Methods start, stop, and said
protected RMICallbackServer server;
public synchronized void start () throws RemoteException, NotBoundException {
if (server == null) {
Registry registry = LocateRegistry.getRegistry (host);
server = (RMICallbackServer) registry.lookup
(RMICallbackServer.REGISTRY_NAME);
server.register (this);
frame.setVisible (true);
}
}
public synchronized void stop () throws RemoteException {
frame.setVisible (false);
RMICallbackServer server = this.server;
this.server = null;
if (server != null)
server.deregister (this);
}
public void said (String message) {
output.append (message + "\n");
}
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Method actionPerformed
public void actionPerformed (ActionEvent ev) {
try {
RMICallbackServer server = this.server;
if (server != null) {
server.say (ev.getActionCommand ());
input.setText ("");
}
} catch (RemoteException ex) {
input.setVisible (false);
frame.validate ();
ex.printStackTrace ();
}
}
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Method main
public static void main (String[] args) throws RemoteException, NotBoundException {
if (args.length != 1)
throw new IllegalArgumentException
("Syntax: RMICallbackClientImpl <host>");
RMICallbackClientImpl callbackClient =
new RMICallbackClientImpl (args[0]);
callbackClient.start ();
}
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Disadvantages of Example


For every client, need to maintain two
network connections, one incoming and one
outgoing
Connections will timeout and need to be
periodically reestablished
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An RMI Distributed List Example
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

Client and server maintain list state in local
IDList object
When an update is attempted to a client list,
makes a remote method call on server
If server approves the change, it makes
remote method calls on all registered clients
to indicate the change
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Distributed List Data Structure
List
List
Object1
addElement()
Object1
Object2
Object4
Object2
Object3
Object3
List
updateElement()
List
Object1
replaceElement()
Object1
Object3,
Object2
Object2,
Object5
Object5
Object5
Object6
Object4
Object4
Object4
Object6
List
Enumeration
Object5
Object4
Object6
elements()
Object5
Object4
removeElement()
Object1
Object6
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Interface DistributedList
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.util.*;
public interface DistributedList {
public abstract void addElement (Object element);
public abstract void updateElement (Object oldElement, Object newElement);
public abstract void replaceElement (Object oldElement, Object newElement);
public abstract void removeElement (Object element);
public abstract Enumeration getElements ();
public abstract void addChangeListener (ChangeListener listener);
public abstract void removeChangeListener (ChangeListener listener);
}
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Interface ChangeListener
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.util.*;
public interface ChangeListener extends EventListener {
public abstract void changeOccurred (ChangeEvent changeEvent);
}
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Class ChangeEvent
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.util.*;
public class ChangeEvent extends EventObject {
public ChangeEvent (Object source) {
super (source);
}
}
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Class ID
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.io.*;
public class ID implements Serializable {
protected int id;
public ID (int id) {
this.id = id;
}
public boolean equals (Object other) {
return (other != null) && (other instanceof ID) && (((ID) other).id == id);
}
}
public int hashCode () {
return id;
}
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Class IDList
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.io.*;
import java.util.*;
public class IDList implements Serializable {
// public IDList () …
// public synchronized ID allocateID () …
// public synchronized boolean addElement (ID id, Object element) …
// public synchronized boolean updateElement (ID oldID, ID id, Object element) …
// public synchronized boolean replaceElement (ID oldID, ID id, Object element) …
// public synchronized boolean removeElement (ID id) …
// public synchronized ID getID (Object element) …
// public Enumeration getElements () …
// public synchronized Object clone () …
}
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Constructor IDList
protected Vector ids, elements;
public IDList () {
ids = new Vector ();
elements = new Vector ();
}
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Methods of IDList
protected int id;
public synchronized ID allocateID () {
return new ID (id ++);
}
protected int updateCount;
public int getUpdateCount () {
return updateCount;
}
public synchronized boolean addElement (ID id, Object element) {
if (ids.contains (id))
return false;
ids.addElement (id);
elements.addElement (element);
++ updateCount;
return true;
}
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Methods of IDList
public synchronized boolean updateElement (ID oldID, ID id, Object element) {
int index = ids.indexOf (oldID);
if (index < 0)
return false;
ids.setElementAt (id, index);
elements.setElementAt (element, index);
++ updateCount;
return true;
}
public synchronized boolean replaceElement (ID oldID, ID id, Object element) {
int index = ids.indexOf (oldID);
if (index < 0)
return false;
ids.removeElementAt (index);
elements.removeElementAt (index);
ids.addElement (id);
elements.addElement (element);
++ updateCount;
return true;
}
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Methods of IDList
public synchronized boolean removeElement (ID id) {
int index = ids.indexOf (id);
if (index < 0)
return false;
ids.removeElementAt (index);
elements.removeElementAt (index);
++ updateCount;
return true;
}
public synchronized ID getID (Object element) {
int index = elements.indexOf (element);
if (index < 0)
return null;
else
return (ID) ids.elementAt (index);
}
public Enumeration getElements () {
return ((Vector) elements.clone ()).elements ();
}
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Methods of IDList
public synchronized Object clone () {
try {
IDList idList = (IDList) super.clone ();
idList.ids = (Vector) ids.clone ();
idList.elements = (Vector) elements.clone ();
return idList;
} catch (CloneNotSupportedException ignored) {
return null;
}
}
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Interface RMIListServer
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.rmi.*;
public interface RMIListServer extends Remote {
public abstract IDList register (RMIListClient client) throws RemoteException;
public abstract void deregister (RMIListClient client) throws RemoteException;
public abstract void addElement (Object element) throws RemoteException;
public abstract void updateElement (ID id, Object newElement) throws RemoteException;
public abstract void replaceElement (ID id, Object newElement) throws RemoteException;
public abstract void removeElement (ID id) throws RemoteException;
}
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Interface RMIListClient
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import java.rmi.*;
public interface RMIListClient extends Remote {
public abstract void elementAdded (ID id, Object element) throws RemoteException;
public abstract void elementUpdated (ID oldID, ID id, Object element) throws
RemoteException;
public abstract void elementReplaced (ID oldID, ID id, Object element) throws
RemoteException;
public abstract void elementRemoved (ID id) throws RemoteException;
}
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Class RMIListServerImpl
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import
import
import
import
java.rmi.*;
java.util.*;
java.rmi.server.*;
java.rmi.registry.*;
public class RMIListServerImpl extends UnicastRemoteObject implements RMIListServer {
// public RMIListServerImpl () throws RemoteException …
// public synchronized IDList register (RMIListClient client) …
// public synchronized void deregister (RMIListClient client) …
// public synchronized void addElement (Object element) …
// public synchronized void updateElement (ID id, Object element) …
// public synchronized void replaceElement (ID id, Object element) …
// public synchronized void removeElement (ID id) …
// public static void main (String[] args) throws RemoteException, AlreadyBoundException …
}
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Constructor RMIListServerImpl
protected IDList idList;
protected Vector clients;
public RMIListServerImpl () throws RemoteException {
idList = new IDList ();
clients = new Vector ();
}
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Methods of RMIListServerImpl
public synchronized IDList register (RMIListClient client) {
clients.addElement (client);
return idList;
}
public synchronized void deregister (RMIListClient client) {
clients.removeElement (client);
}
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Methods of RMIListServerImpl
public synchronized void addElement (Object element) {
ID id = idList.allocateID ();
if (idList.addElement (id, element)) {
for (int i = 0; i < clients.size (); ++ i) {
try {
((RMIListClient) clients.elementAt (i)).elementAdded (id, element);
} catch (RemoteException ex) {
clients.removeElementAt (i --);
}
}
}
}
public synchronized void updateElement (ID id, Object element) {
ID newID = idList.allocateID ();
if (idList.updateElement (id, newID, element)) {
for (int i = 0; i < clients.size (); ++ i) {
try {
((RMIListClient) clients.elementAt (i)).elementUpdated (id, newID, element);
} catch (RemoteException ex) {
clients.removeElementAt (i --);
}
}
}
}
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Methods of RMIListServerImpl
public synchronized void replaceElement (ID id, Object element) {
ID newID = idList.allocateID ();
if (idList.replaceElement (id, newID, element)) {
for (int i = 0; i < clients.size (); ++ i) {
try {
((RMIListClient) clients.elementAt (i)).elementReplaced (id, newID, element);
} catch (RemoteException ex) {
clients.removeElementAt (i --);
}
}
}
}
public synchronized void removeElement (ID id) {
if (idList.removeElement (id)) {
for (int i = 0; i < clients.size (); ++ i) {
try {
((RMIListClient) clients.elementAt (i)).elementRemoved (id);
} catch (RemoteException ex) {
clients.removeElementAt (i --);
}
}
}
}
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Method main
public static void main (String[] args) throws RemoteException,
AlreadyBoundException {
if (args.length != 2)
throw new IllegalArgumentException
("Syntax: RMIListServerImpl <port> <service>");
RMIListServerImpl listServer = new RMIListServerImpl ();
Registry registry = LocateRegistry.createRegistry
(Integer.parseInt (args[0]));
registry.bind (args[1], listServer);
}
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Class RMIListClientImpl
/* Java Network Programming, Second Edition
* Merlin Hughes, Michael Shoffner, Derek Hamner
* Manning Publications Company; ISBN 188477749X
*
* http://nitric.com/jnp/
*
* Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
* all rights reserved; see license.txt for details. */
import
import
import
import
java.rmi.*;
java.util.*;
java.rmi.server.*;
java.rmi.registry.*;
public class RMIListClientImpl implements DistributedList {
// public RMIListClientImpl (String host, int port, String service) …
// public synchronized void start () throws RemoteException, NotBoundException …
// public synchronized void stop () throws RemoteException …
// public synchronized void addElement (Object element) …
// public synchronized void updateElement (Object oldElement, Object newElement) …
// public synchronized void replaceElement (Object oldElement, Object newElement) …
// public synchronized void removeElement (Object element) …
// public Enumeration getElements () …
// public void addChangeListener (ChangeListener listener) …
// public void removeChangeListener (ChangeListener listener) …
// protected void fireChangeEvent (ChangeEvent changeEvent) …
// class Callback implements RMIListClient …
}
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Constructor RMIListClientImpl
protected String host, service;
protected int port;
public RMIListClientImpl (String host, int port, String service) {
this.host = host;
this.port = port;
this.service = service;
}
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Methods of RMIListClientImpl
protected IDList idList;
protected RMIListClient myself;
protected RMIListServer listServer;
public synchronized void start () throws RemoteException, NotBoundException {
if (listServer == null) {
myself = (RMIListClient)
UnicastRemoteObject.exportObject (new Callback ());
Registry registry = LocateRegistry.getRegistry (host, port);
listServer = (RMIListServer) registry.lookup (service);
try {
idList = listServer.register (myself);
} catch (RemoteException ex) {
listServer = null;
throw ex;
}
fireChangeEvent (new ChangeEvent (this));
}
}
public synchronized void stop () throws RemoteException {
try {
if (listServer != null)
listServer.deregister (myself);
} finally {
listServer = null;
UnicastRemoteObject.unexportObject (myself, true);
}
}
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Methods of RMIListClientImpl
public synchronized void addElement (Object element) {
if (listServer != null) {
try {
listServer.addElement (element);
} catch (RemoteException ex) {
listServer = null;
}
}
}
public synchronized void updateElement (Object oldElement, Object newElement) {
if (listServer != null) {
ID id = idList.getID (oldElement);
if (id != null) {
try {
listServer.updateElement (id, newElement);
} catch (RemoteException ex) {
listServer = null;
}
}
}
}
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Methods of RMIListClientImpl
public synchronized void replaceElement (Object oldElement, Object newElement) {
if (listServer != null) {
ID id = idList.getID (oldElement);
if (id != null) {
try {
listServer.replaceElement (id, newElement);
} catch (RemoteException ex) {
listServer = null;
}
}
}
}
public synchronized void removeElement (Object element) {
if (listServer != null) {
ID id = idList.getID (element);
if (id != null) {
try {
listServer.removeElement (id);
} catch (RemoteException ex) {
listServer = null;
}
}
}
}
public Enumeration getElements () {
return idList.getElements ();
}
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Methods of RMIListClientImpl
protected Vector listeners = new Vector ();
public void addChangeListener (ChangeListener listener) {
listeners.addElement (listener);
}
public void removeChangeListener (ChangeListener listener) {
listeners.removeElement (listener);
}
protected void fireChangeEvent (ChangeEvent changeEvent) {
synchronized (listeners) {
for (int i = 0; i < listeners.size (); ++ i)
((ChangeListener) listeners.elementAt (i)).changeOccurred (changeEvent);
}
}
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Inner Class Callback
class Callback implements RMIListClient {
public void elementAdded (ID id, Object element) {
idList.addElement (id, element);
fireChangeEvent (new ChangeEvent (RMIListClientImpl.this));
}
public void elementUpdated (ID oldID, ID id, Object element) {
idList.updateElement (oldID, id, element);
fireChangeEvent (new ChangeEvent (RMIListClientImpl.this));
}
public void elementReplaced (ID oldID, ID id, Object element) {
idList.replaceElement (oldID, id, element);
fireChangeEvent (new ChangeEvent (RMIListClientImpl.this));
}
}
public void elementRemoved (ID id) {
idList.removeElement (id);
fireChangeEvent (new ChangeEvent (RMIListClientImpl.this));
}
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Summary of RMI



RMI framework hides low-level networking details in
the guise of remote method calls
Different style than using streams and sockets
Each style has its own uses


Sockets are useful when interacting with other socket-based
applications and when full control of communication channel
is needed
RMI is good in designing cleaner high-level protocols, in
request-based applications, and in peer-to-peer applications
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Next Class



Telnet and rlogin
File transfer protocol (FTP)
Read TI Ch. 26, 27
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