A Simple Chat Application

This is a simple chat application. The basic idea is to have several client applets who chat with each other. That is, what they type in their TextFields appears on every client's TextArea---a chat session. To do this, each client must first register with a server (an act that is posted to all current clients). When a client contributes a comment, it is sent to the server, who forwards the message to each of the clients.

This basic logic could, for example, be used to implement a collaborative "white board" application.

Client operations include:

register with the chat server by typing your "name" into a Dialog box. Your name is a string by which other clients will distinguish your messages from all others. No attempt is made to force ensure uniqueness. Hey, this is a simple chat application. You can supe it up.
listChatters all current participants.
clear your TextArea. This does not clear the TextArea of other clients.
unregister from the chat session.

The files needed are:

ChatServer.java: The server remote interface.
ChatServerImpl.java: The application that implements the ChatServer remote interface.
Talker.java: A thread that buffers the server's communication with the client.
Message.java: A simple message object.

Chat.java: The chat client remote interface.
ChatImpl.java: The applet that implements the Chat remote interface.
ServerTalker.java: A thread that buffers the client's communication with the server.
NameDialog.java: A Dialog box that takes the clients "name".

Regarding names, Talker and ServerTalker seem backward. I am calling it ServerTalker because it "talks" to the server. Bad choice. I know.

Everything is in packages. The NameDialog class, following the author's intentions, is put in examples.util; all other classes are put in examples.chat. I have a similar structure for the source files. That is, I have directories named:

$home/java/examples/chat
$home/java/examples/util

$home/class/examples/chat
$home/class/examples/util

Compile and Deploy Class Files

Compile the Java source files

$HOME/class

$HOME/java/examples/chat

CLASSPATH

To compile the Java source files, run the javac command as follows:

javac -d $HOME/class *.java

This command creates the directory examples/chat (if it does not already exist) in the directory $HOME/class.

javac

Solaris javac manual page

Win32 javac manual page

Use `rmic` to generate skeletons and/or stubs

rmic

MyImpl_Skel.class

MyImpl_Stub.class

For our example, to create the stub and skeleton for the HelloImpl remote object implementation, run rmic like this:

rmic -d $HOME/class examples.chat.ChatImpl examples.chat.ChatServerImpl

Start the server and client

Create the HTML file

<html>

<applet code="examples.chat.ChatImpl.class"

width=800

height=400

>

</applet>

</html>

Start the server

For Solaris:

java examples.chat.ChatServerImpl &

For Windows:

java examples.chat.ChatServerImpl

Run the client
Once the server is running, the client can be launched as follows (while in $HOME/class/examples/chat):
appletiewer ChatApplet.html
Good luck!

Enhancements

Serialize Messages yourself (within the Message class):

private void writeObject( ObjectOutputStream out ) throws IOException

{

out.writeUTF( sender );

out.writeUTF( message );

}

private void readObject( ObjectInputStream in ) throws IOException, ClassNotFoundException
{
sender = in.readUTF();
message = in.readUTF();
}

Threadpooling instead of having 1 Talker for each ChatClient.
RMI Activation to restart server.