Примеры применения сервера-клиента-чата на JAVA

Здесь идет программа multiThreading :) сервер имеет два класса, а клиент - один. Надеюсь, вам понравится!

ГЛАВНЫЙ КЛАСС СЕРВЕР:

    import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;


public class Main {

    public static void main(String[] args) throws IOException {
        int MAXCLIENTS = 20;
        int port = 4444;
        ServerSocket server = null;
        Socket clientSocket = null;
        // An array of clientsConnected instances
        ClientThread[] clientsConnected = new ClientThread[MAXCLIENTS];

        try {
            server = new ServerSocket(port);
            System.out.println("listening on port: " + port);
        } catch (IOException e) {// TODO Auto-generated catch block
            e.printStackTrace();

        }

        while (true) {
            try {
                clientSocket = server.accept();

            } catch (IOException e) {
                e.printStackTrace();
                if (!server.isClosed()){server.close();}
                if (!clientSocket.isClosed()){clientSocket.close();}
            }

            System.out.println("Client connected!");

            for (int c = 0; c < clientsConnected.length; c++){
                if (clientsConnected[c] == null){
                    // if it is empty ( null) then start a new Thread, and pass the socket and the object of itself as parameter
                    (clientsConnected[c] = new ClientThread(clientSocket, clientsConnected)).start();
                    break; // have to break, else it will start 20 threads when the first client connects :P
                }
            }
        }

    }



}

СЕРВЕРНЫЙ КЛИЕНТ КЛИЕНТА:

    import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;


public class ClientThread extends Thread{

    private ClientThread[] clientsConnected;
    private Socket socket = null;
    private DataInputStream in = null;
    private DataOutputStream out = null;
    private String clientName = null;

    //Constructor
     public ClientThread(Socket socket, ClientThread[] clientsConnected){
        this.socket = socket;
        this.clientsConnected = clientsConnected;
    }

    public void run(){
        try {
            // Streams :)
            in = new DataInputStream(socket.getInputStream());
            out = new DataOutputStream(socket.getOutputStream());

            String message = null;

            clientName = in.readUTF();

            while (true){
                message = in.readUTF();

                for (int c = 0; c < clientsConnected.length; c++){
                    if (clientsConnected[c]!= null && clientsConnected[c].clientName != this.clientName){ //dont send message to your self ;)
                        clientsConnected[c].sendMessage(message, clientName); // loops through all the list and calls the objects sendMessage method.
                    }
                }

            }

        } catch (IOException e) {
            System.out.println("Client disconnected!");
            this.clientsConnected = null;
        }
    }
    // Every instance of this class ( the client ) will have this method.
    private void sendMessage(String mess, String name){
        try {
            out.writeUTF(name + " says: " + mess);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

И НАКОНЕЦ КЛИЕНТА:

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.util.Scanner;

public class Main  
{
   public static void main(String[] args) throws IOException {

       Main m = new Main();
       m.connect();
   }

   public void connect() throws IOException{
     //declare a scanner so we can write a message
       Scanner keyboard = new Scanner(System.in);


       // localhost ip
       String ip = "127.0.0.1";
       int port = 4444;
       Socket socket = null;

       System.out.print("Enter your name: ");
       String name = keyboard.nextLine();

       try {

       //connect
       socket = new Socket(ip, port);

       //initialize streams
       DataInputStream in = new DataInputStream(socket.getInputStream());
       DataOutputStream out = new DataOutputStream(socket.getOutputStream());

       //start a thread which will start listening for messages
       new ReceiveMessage(in).start();

       // send the name to the server!
       out.writeUTF(name);

       while (true){
           //Write messages :)
           String message = keyboard.nextLine();
           out.writeUTF(message);
       }

       }
       catch (IOException e){
           e.printStackTrace();
            if (!socket.isClosed()){socket.close();}
       }
   }

   class ReceiveMessage extends Thread{

       DataInputStream in;

       ReceiveMessage(DataInputStream in){
           this.in = in;
       }

       public void run(){
           String message;
           while (true){
               try {
                    message = in.readUTF();
                    System.out.println(message);

                } catch (IOException e) {
                e.printStackTrace();
                }

           }
       }

   }

}

Я запустил сервер в eclipse и начал два клиента из CMD, выглядит так: