Chat de consola en java basado en la version de https://www.daniweb.com/programming/software-development/code/448361/multithreaded-simple-clientserver-chat-console-program

Client.java

package ttext;

import java.io.*;
import java.net.*;

public class Client {
	public static void main() {
		try {
			Socket sock = new Socket("localhost", 8000);
			SendThread sendThread = new SendThread(sock);
	
			Thread thread = new Thread(sendThread);
			thread.start();
			RecieveThread recieveThread = new RecieveThread(sock);
	
			Thread thread2 =new Thread(recieveThread);
			thread2.start();
		} catch (Exception e) {
			System.out.println(e.getMessage());
		} 
	}
}
class RecieveThread implements Runnable {
	Socket sock = null;
	BufferedReader recieve = null;
	
	public RecieveThread(Socket sock) {
		this.sock = sock;
	}
	
	public void run() {
		try {
			recieve = new BufferedReader(new InputStreamReader(this.sock.getInputStream()));
			String msgRecieved = null;
			
			while((msgRecieved = recieve.readLine())!= null) {
				System.out.println("Servidor: " + msgRecieved);
				System.out.println("Su mensaje para el servidor..");
			}
		} catch(Exception e) {
			System.out.println(e.getMessage());
		}
	}
}
class SendThread implements Runnable {
	Socket sock = null;
	PrintWriter print = null;
	BufferedReader brinput = null;
	
	public SendThread(Socket sock) {
		this.sock = sock;
	}
	
	public void run(){
		try {
			if(sock.isConnected()) {
				System.out.println("Conectado a " + sock.getInetAddress() + " en el puerto " + sock.getPort());
				this.print = new PrintWriter(sock.getOutputStream(), true);

				while(true) {
					System.out.println("Escriba su mensaje... (O escriba 'SALIR' para cerrar)");
					brinput = new BufferedReader(new InputStreamReader(System.in));

					String msgtoServerString = null;
					msgtoServerString = brinput.readLine();
					this.print.println(msgtoServerString);
					this.print.flush();
				
					if(msgtoServerString.equals("SALIR"))
					break;
				}
				sock.close();
			}
		} catch(Exception e) {
			System.out.println(e.getMessage());
		}
	}
}

Server.java

package ttext;

import java.io.*;
import java.net.*;
import java.lang.*;

public class Server {
	public static void main() throws IOException {
		final int port = 8000;
		System.out.println("Experando conexion en el puerto " + port);
		ServerSocket ss = new ServerSocket(port);
		Socket clientSocket = ss.accept();
		System.out.println("Conexion entrante de " + clientSocket.getInetAddress());

		RecieveFromClientThread recieve = new RecieveFromClientThread(clientSocket);
		Thread thread = new Thread(recieve);
		thread.start();
		SendToClientThread send = new SendToClientThread(clientSocket);
		Thread thread2 = new Thread(send);
		thread2.start();
	}
}

class RecieveFromClientThread implements Runnable {
	Socket clientSocket=null;
	BufferedReader brBufferedReader = null;
	
	public RecieveFromClientThread(Socket clientSocket) {
		this.clientSocket = clientSocket;
	}

	public void run() {
		try {
			brBufferedReader = new BufferedReader(new InputStreamReader(this.clientSocket.getInputStream()));		
			
			String messageString;
			while(true) {
				while((messageString = brBufferedReader.readLine()) != null){
					if(messageString.equals("SALIR"))
						break;

					System.out.println("Cliente: " + messageString);
					System.out.println("Respuesta al cliente..");
				}
				this.clientSocket.close();
				System.exit(0);
			}
		
		} catch(Exception ex) { 
			System.out.println(ex.getMessage()); 
		}
	}
}
class SendToClientThread implements Runnable {
	PrintWriter pwPrintWriter;
	Socket clientSock = null;
	
	public SendToClientThread(Socket clientSock) {
		this.clientSock = clientSock;
	}

	public void run() {
		try {
			pwPrintWriter =new PrintWriter(new OutputStreamWriter(this.clientSock.getOutputStream()));
			
			while(true) {
				String msgToClientString = null;
				BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
				
				msgToClientString = input.readLine();
				
				pwPrintWriter.println(msgToClientString);
				pwPrintWriter.flush();
				System.out.println("Su mensaje para el cliente..");
			}
		} catch(Exception ex) {
			System.out.println(ex.getMessage());
		}	
	}
}

TText.java

package ttext;

import java.io.*;

public class TText {
	
	/**
	* @param args the command line arguments
	*/
	public static void main(String[] args) {
		if(args[0].equals("-s")) {
			try {
				Server.main();
			} catch(IOException e) {
				System.out.println("Parece que hubo algun tipo de error en la conexion");
			}
		} else {
			Client.main();
		}
	}
}