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How to implement a chat client

I'm having trouble interpreting a question for a college assignment. It seems my solution is not an acceptable answer. I'm not looking for the solution just mainly an explanation on what I'm doing wrong.
The question is:
Implement a simple chat client which transmits user messages to a multicast address and receives messages sent from other clients on other machines sent to the same multicast address.
The way I am interpreting this is that I have is a server class with a multicast address, then n-amount of client classes that connect or join the server group.
Then when the client has connected to the server class. The server sends the same typed message out to the multiple clients which is displayed on screen of the client. Am I way off with whats asked??. My code for the multicast server is,
package multicastchatter;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.UnknownHostException;
public class multicastServer {
final static String INet_addr = "224.0.0.3";
final static int PORT = 8888;
public static void main(String[] args) throws InterruptedException, UnknownHostException {
InetAddress addr = InetAddress.getByName(INet_addr);
try(DatagramSocket serverSocket = new DatagramSocket())//open the datagram
{
for(int i = 0; i<5; i++)
{
String message = "Sent message number "+i;
//create a packet and send
DatagramPacket messPack = new DatagramPacket(message.getBytes(),message.getBytes().length, addr, PORT);
serverSocket.send(messPack);
System.out.println("The server says"+ message);
Thread.sleep(500);
}
}
catch(IOException e)
{
e.printStackTrace();
}
}
}
and my multicast client is
package multicastchatter;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;
import java.net.UnknownHostException;
public class multicastClient {
final static String INet_addr = "224.0.0.3";
final static int PORT = 8888;
//final static int PORT = 8080;
public static void main(String[] args) throws UnknownHostException {
InetAddress address = InetAddress.getByName(INet_addr);//get address
byte[] buf = new byte[256];//create a buffer of bytes
//create the multicast socket
try(MulticastSocket clientSocket = new MulticastSocket(PORT))
{
clientSocket.joinGroup(address);//join the group
while(true)
{//recieve the info
DatagramPacket messPack = new DatagramPacket(buf, buf.length);
clientSocket.receive(messPack);
String message = new String(buf, 0, buf.length);
System.out.println("Socket recieved message saying" + message+ " by "+ messPack.getAddress());
}
}
catch(IOException e)
{
e.printStackTrace();
}
}
}
Any advice is appreciated. All I can think off is that I need to send messages back to the server from the client?

Being that your question is asking if your conceptualization of the client-server architecture is correct, then yes. What your teacher wants is a server that accepts client connections, and broadcasts client messages it receives to all clients.
A multi-threaded server approach is typically chosen in this situation, as many concurrent connections are being utilized, and each of them waits for a message. Upon receiving the message, the server will take that message, append an identifier to the front so that we know what client said the message, and distribute that message once only to each client.
As for the client, it just takes input, sending when necessary, and always listens for packets from the server, displaying whatever it receives. A valuable word of advice:
Do not allow the client side to display what is sent until it is received. In other words, sending input from the client program should only display what was sent when it is received back from the server. It is a good practice to employ in server-client architecture in most instances.

Connection time out in Java Server-Client

I have a small program where a Server-Client program is getting connected on the same network, but the same program shows a connection time out error in the client program. I have connected the two systems using LAN cable.
Server
import java.io.IOException;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;
public class DateServer {
public static void main(String[] args) throws IOException {
ServerSocket listener = new ServerSocket(9090);
try {
while (true) {
Socket socket = listener.accept();
try {
PrintWriter out =
new PrintWriter(socket.getOutputStream(), true);
out.println(new Date().toString());
} finally {
socket.close();
}
}
} finally {
listener.close();
}
}
}
Client
import java.io.BufferedReader;
import java.io.IOException ;
import java.io.InputStreamReader;
import java.net.Socket;
import javax.swing.JOptionPane;
public class DateClient {
public static void main(String[] args) throws IOException {
String serverAddress = JOptionPane.showInputDialog(
"Enter IP Address of a machine that is\n" +
"running the date service on port 9090:");
Socket s = new Socket(serverAddress, 9090);
BufferedReader input =
new BufferedReader(new InputStreamReader(s.getInputStream()));
String answer = input.readLine();
JOptionPane.showMessageDialog(null, answer);
System.exit(0);
}
}

Since the code runs on the same computer, three possibilities come to my mind:
The problem can be either your firewall/access to port rights or having IP addresses as mentioned by other fellows.
You are setting the IP address of the server wrong.
The IP address of the server does not lie on the subnet mask of your network. If you have literaly connected the two computers with a cable (no routers in the middle) you probably haven't setup a DHCP, i.e., your ip addresses should be manually selected. If the ip is selected randomly, chances are your client computer can't find the server computer. try manually setting the ip addresses of both computers to an invalid address within the same subnet mask range and see if it works.
For example set the following addresses:
client IP: 192.168.1.10
subnetmask: 255.255.255.0
server IP: 192.168.1.11
subnetmask: 255.255.255.0

Connecting the two systems with a LAN cable is not sufficient. You have to ensure they have distinct IP addresses, are both in the same IP subnet, and/or have appropriate IP routing tables defined. More typically you would connect both via a router.

Message passing in Server Socket in Java

I am new in Socket programming of java, i had written two files in Java named Server.java and Client.java as below:
Server.java
import java.io.*;
import java.net.*;
public class Server
{
static ServerSocket server = null;
static Socket socket = null;
static int userConnected=0;
static String msg = "In Server";
public static void main(String []args)throws Exception
{
int port = 1234;
server = new ServerSocket(port);
PrintStream output = null;
while(true)
{
socket=server.accept();
//Connection Arrived
userConnected++;
System.out.println("A new user arrived,\nNo. of user connected "+(userConnected));
}
}
}
Client.java
import java.net.*;
import java.io.*;
public class Client
{
static Socket socket = null;
public static void main(String[] args) throws Exception
{
socket = new Socket("localhost",1234);
}
}
When running Server class file on one system it will create Server on Port 1234 and when i run client class file it get successfully connected to Server on port 1234 and when i run another Client class file by another Console it also get connected to Server on port 1234,
What i want is to perform message passing between these two clients i.e. the message written in first client get shown in second client and vise-versa.
Can anyone please help me ??

http://www.tutorialspoint.com/java/java_networking.htm
I suggest you take a look at this. You can take a horse to the water, but cannot make it drink!

Check out ObjectOutputStream and ObjectInputStream in the standard Java API, you can then send Strings (and any other objects you want).

Sending keyboard presses to another computer?

I was wondering if i could get help making or finding a program that has the ability to send keyboard presses and receive them on another computer. I want to use this to play multiplayer flash-player games with friends across computers. I know there are some programs out there like "logmein" but both users cannot use the keyboard at the same time. (When i press a key the computer user cannot press a key at the same time because it wont respond.) I only know java and I am quite novice at it. Im guessing if i need to write it ill have to send the information through a port or onto a web-server. I would like to know your opinions and suggestions for this program, thanks guys.

Basically what you are looking for is a chatroom program? Have you tried looking into mIRC?
mIRC is a free internet relay chat. What exactly are the requirements for the program? Is there a certain size that it must be? Are these flash games that you and your friends are playing taking up your full computer screen?
Building a program would require a web-server(any computer with internet access would do), and you would have to open the ports on your network to allow the traffic to go through.
A basic server in java would look something like this:
Please note that after the first connection this "server" will close the connection.
import java.net.ServerSocket;
import java.net.Socket;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
public class Server
{
private static ServerSocket serverSocket;
private static Socket clientSocket;
private static BufferedReader bufferedReader;
private static String inputLine;
public static void main(String[] args)
{
// Wait for client to connect on 63400
try
{
serverSocket = new ServerSocket(63400);
while(true){
clientSocket = serverSocket.accept();
// Create a reader
bufferedReader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
// Get the client message
while((inputLine = bufferedReader.readLine()) != null)
{System.out.println(inputLine);}
serverSocket.close();
System.out.println("close");
}
}
catch(IOException e)
{
System.out.println(e);
}
}
}
And a client would almost be the same:
import java.net.Socket;
import java.io.PrintWriter;
public class client
{
private static Socket socket;
private static PrintWriter printWriter;
public static void main(String[] args)
{
try
{
//change "localhost" to the ip address that the client is on, and this number to the port
socket = new Socket("localhost",63400);
printWriter = new PrintWriter(socket.getOutputStream(),true);
printWriter.println("Hello Socket");
}
catch(Exception e)
{
System.out.println(e);
}
}
}
If I am not mistaken printWriter is a 16-bit operation, and in order to reduce lag, if you were just sending text then you might want to use printStream(). I believe that this might be a bit quicker.

How can I configure the source port for a server using Netty to send UDP packets?

I have a server task that uses Netty for socket I/O. It binds to port MY_PORT and receives UDP messages from clients. It responds to these clients, sending messages back to the clients with a destination port of MY_PORT. Using wireshark, I see that the outgoing packets from my server also have a source port of MY_PORT. This all works fine.
The people in charge of the network between the server and clients are having some issues with a load balancer. They said it would help them out if the UDP messages my server sends to the clients had a different source port than the one used for a destination.
I've looked at the Netty API, but I'm not sure how I can do this. It seems that because I've bound to a local port, I must use that for outgoing packets as well?? Here's a stripped down version of my code.
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.net.UnknownHostException;
import java.util.concurrent.Executors;
import org.jboss.netty.bootstrap.ConnectionlessBootstrap;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ChannelPipeline;
import org.jboss.netty.channel.ChannelPipelineFactory;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.channel.MessageEvent;
import org.jboss.netty.channel.SimpleChannelHandler;
import org.jboss.netty.channel.socket.nio.NioDatagramChannelFactory;
public class UdpServer {
private final int port;
private Channel serverChannel;
public UdpServer( int port ) {
super();
this.port = port;
}
public void start() {
NioDatagramChannelFactory serverChannelFactory =
new NioDatagramChannelFactory( Executors.newCachedThreadPool(), 1 );
ConnectionlessBootstrap serverBootstrap =
new ConnectionlessBootstrap( serverChannelFactory );
serverBootstrap.setPipelineFactory( new ChannelPipelineFactory() {
#Override
public ChannelPipeline getPipeline() {
return Channels.pipeline( new SimpleChannelHandler() {
#Override
public void messageReceived( ChannelHandlerContext ctx,
MessageEvent e ) {
// TODO, handle message from client
}
} );
}
} );
serverBootstrap.setOption( "reuseAddress", Boolean.TRUE );
final InetSocketAddress trafficAddress = new InetSocketAddress( port );
serverChannel = serverBootstrap.bind( trafficAddress );
}
public void sendMessage( byte[] message, String clientIp )
throws UnknownHostException {
// TODO, how do I control the source port of this packet??
SocketAddress address =
new InetSocketAddress( InetAddress.getByName( clientIp ), port );
ChannelBuffer buffer = ChannelBuffers.wrappedBuffer( message );
serverChannel.write( buffer, address );
}
}

You're already using bind() to set the local address. You can use connect() to connect to a specific destination port (a stretch of the "connect" concept). On a regular datagram socket you could include the remote port in the send request, but not if you're using write(). In that case you must use connect().

They said it would help them out if the UDP messages my server sends to the clients had a different source port than the one used for a destination.
This sounds like complete hooey to me. Net admins seem to have no idea about how source/destination ports are actually allocated. Even if the clients used system-allocated poets rather than a fixed port, which they probably should, the system could still allocate the same port number as the server is using.
However you could probably shut them up, or at least move them on to a different problem, by having the clients use system-allocated ports rather than a fixed port. Unless there is a client-side firewall of course ...