Communicating Between Threads In Java

Question

I am attempting to make a program that allows for communication between two or more clients. I grabbed most of the source from a site, however I could not find out how to make the two clients actually display what the other client said. Since they run in their own thread I think the server is only giving the text back to the sender's thread only, instead of giving it to everyone connected.

package Server;
import java.net.*;
import java.util.*;
import java.io.*;
import javax.swing.*;
import java.awt.*;

public class Server extends JFrame
{   
//A JTextArea to hold the information received from clients
JTextArea chatBox = new JTextArea();

public static void main(String[] args)
{
    new Server();
}

public Server()
{
    //We need to set up a layout for our window
    setLayout(new BorderLayout());
    //Only display text, do not allow editing
    chatBox.setEditable(false);
    //Add our chatbox in the center with scrolling abilities
    add(new JScrollPane(chatBox), BorderLayout.CENTER);

    setTitle("Chat Server");
    setSize(550,400);
    //If the user closes then exit out
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //Show the frame
    setVisible(true);

    //We need a try-catch because lots of errors can be thrown
    try {
        ServerSocket sSocket = new ServerSocket(8123);
        chatBox.append("Server started at: " + new Date()+"\n");

        //Loop that runs server functions
        while(true) {
            //Wait for a client to connect
            Socket socket = sSocket.accept();
            int Port = socket.getPort();
            InetAddress IP = socket.getInetAddress();
            System.out.println("INFO: Incoming connection from: "+IP+":"+Port);
            chatBox.append("INFO: Incoming connection from: "+IP+":"+Port+"\n");

            //Create a new custom thread to handle the connection
            ClientThread cT = new ClientThread(socket);

            //Start the thread!
            new Thread(cT).start();

        }
    } catch(IOException exception) {
        System.out.println("Error: " + exception);
    }
}

//Here we create the ClientThread inner class and have it implement Runnable
//This means that it can be used as a thread
class ClientThread implements Runnable
{
    Socket threadSocket;

    //This constructor will be passed the socket
    public ClientThread(Socket socket)
    {
        //Here we set the socket to a local variable so we can use it later
        threadSocket = socket;
    }

    public void run()
    {

        //All this should look familiar
        try {
            //Create the streams
            PrintWriter output = new PrintWriter(threadSocket.getOutputStream(), true);
            BufferedReader input = new BufferedReader(new InputStreamReader(threadSocket.getInputStream()));

            //Tell the client that he/she has connected
            output.println("You have connected at: " + new Date());
            chatBox.append("Client connected\n");


                //This will wait until a line of text has been sent
                String chatInput = input.readLine();
                //Add the chat to the text box
                chatBox.append(chatInput+"\n");
                System.out.println(chatInput);
                output.println(chatInput);
            } catch(IOException exception) {
            System.out.println("ERROR: " + exception);
            chatBox.append("ERROR: "+exception);
        } 
        }
    }
}

Answer 1

You maybe looking for a pub/sub scenario in which a single message from the server will be propagated to all the subscribers. Try using JMS. You can find more details here PointToPoint vs Publish/subscribe model in JMS?