Chat Server and Chat Client In Java

I have written a simple chat server that can serve multiple clients using Socket programming and multithreading in Java. Each client can send message to server, which then broadcasts the message to all other clients currently connected.

Each client is identified by a name, which is taken from user at the time of starting the client.

Chat Server

The following is the code for ChatServer.java. Compile and run it first.

// Chat Server runs at port no. 9999
import java.io.*;
import java.util.*;
import java.net.*;
import static java.lang.System.out;
public class  ChatServer {
  Vector<String> users = new Vector<String>();
  Vector<HandleClient> clients = new Vector<HandleClient>();
  public void process() throws Exception  {
      ServerSocket server = new ServerSocket(9999,10);
      out.println("Server Started...");
      while( true) {
 		 Socket client = server.accept();
 		 HandleClient c = new HandleClient(client);
  		 clients.add(c);
     }  // end of while
  }
  public static void main(String ... args) throws Exception {
      new ChatServer().process();
  } // end of main
  public void broadcast(String user, String message)  {
	    // send message to all connected users
	    for ( HandleClient c : clients )
	       if ( ! c.getUserName().equals(user) )
	          c.sendMessage(user,message);
  }
  class  HandleClient extends Thread {
        String name = "";
	BufferedReader input;
	PrintWriter output;
	public HandleClient(Socket  client) throws Exception {
         // get input and output streams
	 input = new BufferedReader( new InputStreamReader( client.getInputStream())) ;
	 output = new PrintWriter ( client.getOutputStream(),true);
	 // read name
	 name  = input.readLine();
	 users.add(name); // add to vector
	 start();
        }
        public void sendMessage(String uname,String  msg)  {
	    output.println( uname + ":" + msg);
	}
		
        public String getUserName() {  
            return name; 
        }
        public void run()  {
    	     String line;
	     try    {
                while(true)   {
		 line = input.readLine();
		 if ( line.equals("end") ) {
		   clients.remove(this);
		   users.remove(name);
		   break;
                 }
		 broadcast(name,line); // method  of outer class - send messages to all
	       } // end of while
	     } // try
	     catch(Exception ex) {
	       System.out.println(ex.getMessage());
	     }
        } // end of run()
   } // end of inner class
} // end of Server

Chat Client

The following is the code for ChatClient.java. It prompts user to enter name and identifies the client with that name. Server is assumed to run on the same system (localhost) at port number 9999. Run client once for each user by going to a different command prompt.

import java.io.*;
import java.util.*;
import java.net.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import static java.lang.System.out;
public class  ChatClient extends JFrame implements ActionListener {
    String uname;
    PrintWriter pw;
    BufferedReader br;
    JTextArea  taMessages;
    JTextField tfInput;
    JButton btnSend,btnExit;
    Socket client;
    
    public ChatClient(String uname,String servername) throws Exception {
        super(uname);  // set title for frame
        this.uname = uname;
        client  = new Socket(servername,9999);
        br = new BufferedReader( new InputStreamReader( client.getInputStream()) ) ;
        pw = new PrintWriter(client.getOutputStream(),true);
        pw.println(uname);  // send name to server
        buildInterface();
        new MessagesThread().start();  // create thread to listen for messages
    }
    
    public void buildInterface() {
        btnSend = new JButton("Send");
        btnExit = new JButton("Exit");
        taMessages = new JTextArea();
        taMessages.setRows(10);
        taMessages.setColumns(50);
        taMessages.setEditable(false);
        tfInput  = new JTextField(50);
        JScrollPane sp = new JScrollPane(taMessages, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        add(sp,"Center");
        JPanel bp = new JPanel( new FlowLayout());
        bp.add(tfInput);
        bp.add(btnSend);
        bp.add(btnExit);
        add(bp,"South");
        btnSend.addActionListener(this);
        btnExit.addActionListener(this);
        setSize(500,300);
        setVisible(true);
        pack();
    }
    
    public void actionPerformed(ActionEvent evt) {
        if ( evt.getSource() == btnExit ) {
            pw.println("end");  // send end to server so that server knows about the termination
            System.exit(0);
        } else {
            // send message to server
            pw.println(tfInput.getText());
        }
    }
    
    public static void main(String ... args) {
    
        // take username from user
        String name = JOptionPane.showInputDialog(null,"Enter your name :", "Username",
             JOptionPane.PLAIN_MESSAGE);
        String servername = "localhost";  
        try {
            new ChatClient( name ,servername);
        } catch(Exception ex) {
            out.println( "Error --> " + ex.getMessage());
        }
        
    } // end of main
    
    // inner class for Messages Thread
    class  MessagesThread extends Thread {
        public void run() {
            String line;
            try {
                while(true) {
                    line = br.readLine();
                    taMessages.append(line + "\n");
                } // end of while
            } catch(Exception ex) {}
        }
    }
} //  end of client

The following screenshot shows the program in execution with two clients.