Threads java.lang.NullPointerException

Hi there I was wondering if anyone can help me please.

I ve been working on a simple chat server program and it works when the
server handles one client at the time. I ve been trying to make the
server able to answer clients requests at the same time with threads.

I always get the same error message when I run the server:

java.lang.NullPointerException

at chatserverq3.ServerGUI.processClientRequests(ServerGUI.java:113)

at chatserverq3.ServerGUI.run(ServerGUI.java:73)

at java.lang.Thread.run(Thread.java:484)

This is the client code:

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;


public class ClientGUI extends JFrame implements ActionListener
{
private JTextField nameField;
private JLabel nameLabel;
private JLabel areaLabel;
private JPanel topPanel, botPanel;
private JButton connectButton;
private JTextArea listArea;

private InputStream is;
private OutputStream os;
private BufferedReader fromServer;
private Socket socket;
private PrintWriter toServer;


static final String SERVER_ADDRESS = "127.0.0.1";
static final int SERVER_PORT_NUMBER = 4000;
static final String CLIENT_LOGGINGOFF = "Exit";

//constructor for the client GUI
public ClientGUI(String title)
{
setSize(400, 400);
setTitle(title);
setLocation(100, 100);
nameLabel = new JLabel("Name");
nameField = new JTextField(10);
areaLabel = new JLabel("Connected Users");
topPanel = new JPanel();
topPanel.setLayout(new BorderLayout());
botPanel = new JPanel();
connectButton = new JButton("Connect");
connectButton.addActionListener(this);
listArea = new JTextArea(10, 30);
JScrollPane scr = new JScrollPane(listArea);

topPanel.add(nameField, "West");
topPanel.add(nameLabel, "Center");
topPanel.add(connectButton, "East");

botPanel.add(areaLabel);
botPanel.add(listArea);

getContentPane().add(topPanel, "North");
getContentPane().add(botPanel, "Center");

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

//attempts to connect the client to the server
private void connectServer()
{
try
{
socket = new Socket(SERVER_ADDRESS, SERVER_PORT_NUMBER);
openStreams();
}
catch(IOException e)
{
System.out.println("Trouble contacting the server " + e);
}
}

private void open()throws IOException
{
final boolean AUTO_FLUSH = true;
is = socket.getInputStream();
fromServer = new BufferedReader(new InputStreamReader(is));
os = socket.getOutputStream();
toServer = new PrintWriter(os, AUTO_FLUSH);
}

//action performed when the client GUI button is pressed
public void actionPerformed(ActionEvent a)
{
String buttonLabel = connectButton.getText();
String userName = nameField.getText();
try
{
if((buttonLabel == "Connect")&&(userName.length()> 0))
{
connectToServer();
sendUserName(userName);
connectButton.setText("Disconnect");
}
else
{
logOff(userName);
connectButton.setText("Connect");
}

}
catch(IOException e)
{
System.out.println("Problem with the server " + e);
}
}

private void close()throws IOException
{
toServer.close();
os.close();
fromServer.close();
is.close();
}

//sends the user name to the server
private void sendUserName(String aName)throws IOException
{
String reply;
String uName = aName;
toServer.println(uName + " logged on");

reply = fromServer.readLine();
listArea.setText(reply);
}

//notifies the server a client has logged off
private void logOff(String aName)throws IOException
{
String uName = aName;
toServer.println(uName + " logged off");
listArea.setText("");
toServer.println(CLIENT_LOGGINGOFF);
closeStreams();
socket.close();
}
}

public class Main {

public static void main(String[] args)
{
ClientGUI cg = new ClientGUI("ChatClient");
cg.setVisible(true);
}

}

The server code is:


import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import java.util.*;

public class ServerGUI extends JFrame implements Runnable
{
private JTextArea logArea;
private JLabel logLabel;
private JPanel logPanel;

private ServerSocket ss;
private Socket socket;

private InputStream is;
private OutputStream os;

private PrintWriter toClient;
private BufferedReader fromClient;

static final int PORT_NUMBER = 4000;
static final String CLIENT_LOGGINGOFF = "Exit";

//constructor for the Server GUI
public ServerGUI(String title)
{
setSize(400, 400);
setTitle(title);
setLocation(100, 100);
logArea = new JTextArea(15, 30);
JScrollPane scr = new JScrollPane(logArea);
logLabel = new JLabel("Logging history");

logPanel = new JPanel();
logPanel.add(logLabel);
logPanel.add(logArea);

getContentPane().add(logPanel);



setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

//constructor for the server to set the socket to handle a new thread
public ServerGUI(Socket s)
{
socket = s;
}



public void run()
{
try
{
while(true)
{

openStreams();
processClientRequests();
closeStreams();
socket.close();
}
}
catch(IOException e)
{
System.out.println("Trouble with a connection " + e);
}

}

//helper method for the class to set up the streams
private void open() throws IOException
{
final boolean AUTO_FLUSH = true;
is = socket.getInputStream();
fromClient = new BufferedReader(new InputStreamReader(is));
os = socket.getOutputStream();
toClient = new PrintWriter(os, AUTO_FLUSH);
}

//process the string from received from each client
private void processRequests() throws IOException
{
String userName;
String reply;
int numberOfFields = 3;
String [] fieldContents = new String[numberOfFields];
userName = fromClient.readLine();
while(!(userName.equals(CLIENT_LOGGINGOFF)))
{
StringTokenizer tokensIn = new StringTokenizer(userName, " ");
int i = 0;
while(tokensIn.hasMoreTokens())
{
fieldContents[i] = tokensIn.nextToken();
i++;
}

reply = fieldContents[0];
toClient.println(reply);
logArea.append("[ " + reply + " ] "+ fieldContents[1]+"
"+fieldContents[2]+"\n");
userName = fromClient.readLine();
}
}

//helper method to close the streams with each client
private void close() throws IOException
{
toClient.close();
os.close();
fromClient.close();
is.close();
}
}

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

public class ChatHandler
{
static final int PORT_NUMBER = 4000;

public ChatHandler()
{
}

public void run()
{
try
{
ServerSocket server = new ServerSocket(PORT_NUMBER);
while(true)
{
Socket client = server.accept ();
System.out.println ("Accepted from " + client.getInetAddress ());
Thread aThread = new Thread(new ServerGUI(client));
aThread.start ();
}
}
catch(IOException e)
{
System.out.println("Trouble with ServerSocket, port
"+PORT_NUMBER +": " + e);
}
}
}


public class Main {

public static void main(String[] args)
{
ServerGUI sg = new ServerGUI("ChatServer");
sg.setVisible(true);
ChatHandler cH = new ChatHandler();
cH.run();
}

}


It is the first time I use threads and maybe there is something I dont
understand. Can anyone point me to the right direction please? I think
the problem may be with the 2 server constructor but I am not sure how
to solve it.

Cheers Pat

.