Question

I’m writing a chat program in Java using a GUI that looks like this

The idea is to start the server on one computer and the client on another (or multiple) (I’m currently just running both on the same computer). After a server is started, a client enters the host number and port number and hits connect. All of this is working so far. Once connected, either the user or the server can type in the textField and hit Send, and the message can be sent to the server, and the server sends the message to all clients.

my question is: How can I send text from the clients to the server and vice-versa?

I’m having trouble grasping how this would work. The server sits in a while loop and waits for more connections (all which work), so I don’t know how it can accept text and then push it back.

Here’s the entire program so you can compile it and see the problems I’m having:

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;
import java.lang.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketAddress;
import java.io.PrintWriter;
import java.util.Scanner;

public class Chat extends Frame implements Runnable, WindowListener, ActionListener, ItemListener
{   

    int port = 44004;
    String host =  "127.0.0.1";
    //GUI objects
    TextField ipAddressField = new TextField();
    TextField portField = new TextField(""+port); 
    TextField hostField = new TextField(host);
    TextField inputBox = new TextField();
    static TextArea conversationBox = new TextArea();
    Button startServerButton = new Button("Start Server");
    Button sendButton = new Button("Send");
    Button changeHost = new Button("Change Host");
    Button changePort = new Button("Change Port");
    Button connectButton = new Button("Connect");
    Button disconnectButton = new Button("Disconnect");
    Label hostLabel = new Label("Host:");
    Label portLabel = new Label("Port:");
    MenuBar mb = new MenuBar();
    Menu colorMenu = new Menu("Color");
    CheckboxMenuItem redItem = new CheckboxMenuItem("Red");
    CheckboxMenuItem blueItem = new CheckboxMenuItem("Blue");
    CheckboxMenuItem orangeItem = new CheckboxMenuItem("Orange");
    CheckboxMenuItem blackItem = new CheckboxMenuItem("Black");

    //runtime variables
    Color color = Color.red;
    volatile boolean kill = false;
    volatile boolean isServer = false;
    volatile boolean isClient = false;
    String connections[];

    //messaging variables
    String message;
    Scanner in;
    PrintWriter out;

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

    ServerSocket server;
    Socket s;
    //gui components

    protected Chat()
    {
        double[] colWeight = {1,1,1,1,1,1};
        double[] rowWeight = {5,1,1,1,1};
        int[] colWidth = {1,1,1,1,1,1};
        int[] rowHeight = {5,1,1,1,1};
        GridBagConstraints c = new GridBagConstraints();
        GridBagLayout gbl = new GridBagLayout();
        gbl.rowHeights = rowHeight;
        gbl.columnWidths = colWidth;
        gbl.columnWeights = colWeight;
        gbl.rowWeights = rowWeight;

        setBounds(100,100,400,600);
        setLayout(gbl);

        //add conversation box
        this.conversationBox.setSize(400, 400);
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 5;
        c.gridheight = 5;
        c.fill = 1;
        c.gridx = 0;
        c.gridy = 0;
        gbl.setConstraints(this.conversationBox, c);

        //input text box
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 4;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 0;
        c.gridy = 5;
        gbl.setConstraints(this.inputBox, c);

        //send button
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 1;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 4;
        c.gridy = 5;
        gbl.setConstraints(this.sendButton, c);

        //host label
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 1;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 0;
        c.gridy = 6;
        gbl.setConstraints(this.hostLabel, c);

        //host input
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 2;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 1;
        c.gridy = 6;
        gbl.setConstraints(this.hostField, c);

        //change host button
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 1;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 3;
        c.gridy = 6;
        gbl.setConstraints(this.changeHost, c);

        //start server button
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 1;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 4;
        c.gridy = 6;
        gbl.setConstraints(this.startServerButton, c);

        //row
        //port label
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 1;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 0;
        c.gridy = 7;
        gbl.setConstraints(this.portLabel, c);

        //port input
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 2;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 1;
        c.gridy = 7;
        gbl.setConstraints(this.portField, c);

        //change port button
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 1;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 3;
        c.gridy = 7;
        gbl.setConstraints(this.changePort, c);

        //connect button
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 1;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 4;
        c.gridy = 7;
        gbl.setConstraints(this.connectButton, c);

        //disconnect button, shunned in the corner
        c.weightx = 1;
        c.weighty = 1;
        c.gridwidth = 1;
        c.gridheight = 1;
        c.fill = 1;
        c.gridx = 4;
        c.gridy = 8;
        gbl.setConstraints(this.disconnectButton, c);

        mb.add(colorMenu);
        colorMenu.add(redItem);
        colorMenu.add(blueItem);
        colorMenu.add(orangeItem);
        colorMenu.add(blackItem);


        add(this.conversationBox);
        add(this.inputBox);
        add(this.sendButton);
        add(this.hostLabel);
        add(this.hostField);
        add(this.changeHost);
        add(this.startServerButton);
        add(this.portLabel);
        add(this.portField);
        add(this.changePort);
        add(this.connectButton);
        add(this.disconnectButton);

        inputBox.addActionListener(this);
        sendButton.addActionListener(this);
        changeHost.addActionListener(this);
        changePort.addActionListener(this);
        startServerButton.addActionListener(this);
        connectButton.addActionListener(this);
        disconnectButton.addActionListener(this);
        hostField.addActionListener(this);
        portField.addActionListener(this);
        redItem.addItemListener(this);
        blueItem.addItemListener(this);
        orangeItem.addItemListener(this);
        blackItem.addItemListener(this);

        setMenuBar(mb);
        addWindowListener(this);
        setResizable(true);
        pack();
        setVisible(true);

        new Thread(this).start();
    }

    public void run()
    {   
        conversationBox.appendText("Session Start.\n");
        inputBox.requestFocus();

        while (!kill)
        {
            if (isServer)
            {
                conversationBox.appendText("Server starting on port " + port + "\n");
                conversationBox.appendText("Waiting for clients...\n");
                startServer();
            }
            if (isClient)
            {
                conversationBox.appendText("Starting connection to host " + host + " on port " + port + "\n");
                startClient();
            }
        }       

    }

    public void startClient()
    {
        try
        {
            Socket c = new Socket(host, port);
            in = new Scanner(c.getInputStream());
            out = new PrintWriter(c.getOutputStream());
            while (true)
            {
                if (in.hasNext())
                {
                    Chat.conversationBox.appendText("You Said: " + message);
                    out.println("Client Said: " + message);
                    out.flush();
                }
            }
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    public void startServer()
    {
        try
        {
            server = new ServerSocket(port);
            while (true)
            {
                s = server.accept();
                conversationBox.appendText("Client connected from " + s.getLocalAddress().getHostName() + "\n");    
            }
        }
        catch (Exception e)
        {
            conversationBox.appendText("An error occurred.\n");
            e.printStackTrace();
            isServer = false;
            reEnableAll();
        }

    }

    public void actionPerformed(ActionEvent e) throws NumberFormatException
    {
        Object o = e.getSource();

        if (o == sendButton || o == inputBox)
        {
            if(inputBox.getText() != "")
            {
                out.println(inputBox.getText());
                inputBox.setText("");
            }
        }
        if (o == changeHost || o == hostField)
        {
            if (hostField.getText() != "" && hostField.getText() != host)
            {
                host = hostField.getText();
                conversationBox.appendText("Host changed to " + host + "\n");
            }
        }
        if (o == changePort || o == portField)
        {
            if (portField.getText() != "" && Integer.valueOf(portField.getText()) != port)
            {
                try
                {
                    port = Integer.valueOf(portField.getText());
                    conversationBox.appendText("Port changed to " + port + "\n");
                }
                catch(NumberFormatException up)
                {
                    throw up; //blargh enter a real value
                }
            }
        }
        if (o == startServerButton)
        {
            isServer = true;
            isClient = false;
            startServerButton.enable(false);
            connectButton.enable(false);
            changeHost.enable(false);
            changePort.enable(false);
            hostField.enable(false);
            portField.enable(false);
        }
        if (o == connectButton)
        {
            isServer = false;
            isClient = true;
            startServerButton.enable(false);
        }
        inputBox.requestFocus();
    }

    public void reEnableAll()
    {
        startServerButton.enable(true);
        connectButton.enable(true);
        changeHost.enable(true);
        changePort.enable(true);
        hostField.enable(true);
        portField.enable(true);
    }

    public void windowClosing(WindowEvent e)
    {
        removeWindowListener(this);
        inputBox.removeActionListener(this);
        sendButton.removeActionListener(this);
        changeHost.removeActionListener(this);
        changePort.removeActionListener(this);
        startServerButton.removeActionListener(this);
        connectButton.removeActionListener(this);
        disconnectButton.removeActionListener(this);
        dispose();
        System.exit(0);
    }
    public void windowClosed(WindowEvent e){}
    public void windowOpened(WindowEvent e){}
    public void windowActivated(WindowEvent e){}
    public void windowDeactivated(WindowEvent e){}
    public void windowIconified(WindowEvent e){}
    public void windowDeiconified(WindowEvent e){}

    public void itemStateChanged(ItemEvent e)
    {
        Object o = e.getSource();
        if (o == redItem)
        {
            redItem.setState(true);
            blueItem.setState(false);
            orangeItem.setState(false);
            blackItem.setState(false);
            color = Color.red;
        }

        if (o == blueItem)
        {
            redItem.setState(false);
            blueItem.setState(true);
            orangeItem.setState(false);
            blackItem.setState(false);
            color = Color.red;          
        }

        if (o == orangeItem)
        {
            redItem.setState(false);
            blueItem.setState(false);
            orangeItem.setState(true);
            blackItem.setState(false);
            color = Color.red;          
        }

        if (o == blackItem)
        {
            redItem.setState(false);
            blueItem.setState(false);
            orangeItem.setState(false);
            blackItem.setState(true);
            color = Color.red;          
        }
    }
}

Answer 1

I test your code, I find that in your startServer() function, you don’t create an OutputStream and InputStream

Modify your startClient function like this: (create two global variables : BufferedWriter bw and BufferedReader br, because we need it in your actionPerformed function)

BufferedWriter bw = null;
BufferedReader br = null;
public void startClient()
{
    try
    {
        Socket c = new Socket(host, port);

        bw = new BufferedWriter(new OutputStreamWriter(c.getOutputStream()));
        br = new BufferedReader(new InputStreamReader(c.getInputStream()));

        char buffer[] = new char[1024];
        while (br.read(buffer) > 0)
        {
            Chat.conversationBox.appendText("You Said: " + new String(buffer));
        }
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }
}

Modify your startServer function like this :

public void startServer()
{
    try
    {
        server = new ServerSocket(port);
        while (true)
        {

            s = server.accept();

            s.getInputStream();

            conversationBox.appendText("Client connected from " + s.getLocalAddress().getHostName() + "\n");

            BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
            BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));

            char buffer[] = new char[1024];
            conversationBox.appendText("Reading....");
            while(br.read(buffer) > 0)
            {
                conversationBox.appendText("Client Say : " + new String(buffer));
                bw.write(buffer);
                bw.flush();
            }
            conversationBox.appendText("Reading Done....");
        }
    }
    catch (Exception e)
    {
        conversationBox.appendText("An error occurred.\n");
        e.printStackTrace();
        isServer = false;
        reEnableAll();
    }
}

And in your actionPerformed function, please modify following codes:

    if (o == sendButton || o == inputBox)
    {
        if (inputBox == null)
        {
            System.out.println("NULL");
        }

        if(inputBox.getText() != "")
        {
            //out.println(inputBox.getText());
            //out.flush();

            try
            {
                bw.write(inputBox.getText());
                bw.flush();
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }

            inputBox.setText("");
        }
    }