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Problems when closing and reopening a JFrame that uses a SwingWorker to send and receive messages

I am developing a messaging application with sockets. I have an initial JFrame that allows the user to choose a contact to connect to, and lets them choose if they'd like to be the client or the server. When they make this choice, it calls a method in which creates the chat window frame, and also uses a SwingWorker to initialise a connection, create an action listner on the send buton of the chat window so that it sends messages when pressed, and creates a SocketListener that is always listening while the window is open.
This works just fine, however if I close the chat window and then reopen it by choosing server or client again, nothing happens - the frame loads up however I cannot send any messages on it.
I'm not sure what the problem is here, could it be that i'm not disposing of the swing worker or the frame properly? Any help would be greatly appreciated and apologies for my lack of knowledge.
Here is the relevent code for this:
public static void server() {
JButton server = new JButton();
server.setText("Server");
server.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
String name = nameChoice;
String ip = ipChoice;
String port = portChoice;
try {
server2(port);
} catch (IOException e1) {
e1.printStackTrace();
} catch (Exception e1) {
e1.printStackTrace();
}
}
});
panel.add(server);
}
public static void server2(String port) throws Exception {
gui.frame();
SwingWorker worker = new SwingWorker() {
#Override
protected Void doInBackground() throws Exception {
sockets.serverSetup(port);
gui.sendButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
String msg = gui.newMsg.getText();
gui.newMsg.setText(null);
try {
sockets.sendMsg(msg);
} catch (IOException e1) {
e1.printStackTrace();
}
}
});
while(gui.open==true) {
sockets.receiveMsg();
}
sockets.closeConnection();
System.out.println("Closed");
return null;
}
};
worker.execute();
}
network
package com.company;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Vector;
public class network {
static ServerSocket s;
static Socket s1;
static OutputStream s1out;
static DataOutputStream dos;
static InputStream s1in;
static chatWindowScreen gui = new chatWindowScreen();
static String st;
public static Vector sentVec = new Vector();
public static Vector receivedVec = new Vector();
public static Vector messages = new Vector();
public static void serverSetup(String port) throws IOException {
System.out.println("Test");
int portInt = Integer.parseInt(port);
s = new ServerSocket(portInt);
s1 = s.accept();
System.out.println("Server set up");
//sendMsg("Hi");
}
public static void clientSetup(String port, String ip) throws IOException {
System.out.println("Test");
int portInt = Integer.parseInt(port);
s1 = new Socket(ip, portInt);
System.out.println("Client set up");
//receiveMsg();
}
public static void closeConnection() throws IOException {
dos.close();
s1out.close();
s1.close();
}
public static void sendMsg(String message) throws IOException {
System.out.println("Test");
s1out = s1.getOutputStream();
dos = new DataOutputStream(s1out);
dos.writeUTF(message);
Calendar cal = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
String t1 = sdf.format(cal.getTime());
message = t1 + " - " + message;
sentVec.add(message);
receivedVec.add("");
messages.add(message);
gui.sent.setText("Sent \n");
for (int i = 0; i < sentVec.size(); i++) {
gui.sent.append(sentVec.get(i) + "\n");
}
gui.received.setText("Received \n");
for (int i = 0; i < receivedVec.size(); i++) {
gui.received.append(receivedVec.get(i) + "\n");
}
System.out.println("complete");
}
public static void receiveMsg() throws IOException {
System.out.println("Test");
s1in = s1.getInputStream();
DataInputStream dis = new DataInputStream(s1in);
st = (dis.readUTF());
Calendar cal = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");
String t1 = sdf.format(cal.getTime());
st = t1 + " - " + st;
receivedVec.add(st);
sentVec.add("");
messages.add(st);
gui.received.setText("Received \n");
for (int i = 0; i < receivedVec.size(); i++) {
gui.received.append((String) receivedVec.get(i) + "\n");
}
gui.sent.setText("Sent \n");
for (int i = 0; i < sentVec.size(); i++) {
gui.sent.append((String) sentVec.get(i) + "\n");
}
}
public static Vector getSentVec() {
return sentVec;
}
public static Vector getReceivedVec() {
return receivedVec;
}
}
chatWindowScreen
package com.company;
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.io.IOException;
import java.util.Vector;
public class chatWindowScreen {
static JFrame frame = new JFrame();
static JPanel panel = new JPanel();
static JTextArea sent;
static JTextArea received;
static JTextArea newMsg;
static JButton sendButton;
public static String msg;
static boolean open = true;
static network sockets = new network();
public static boolean close = false;
public void frame() throws Exception {
System.out.println("GUI opened");
frame.setTitle("Messaging Application");
frame.setSize(500, 500);
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.addWindowListener(new WindowListener() {
#Override
public void windowOpened(WindowEvent e) {
}
#Override
public void windowClosing(WindowEvent e) {
}
#Override
public void windowClosed(WindowEvent e) {
System.out.println("Closed");
panel.removeAll();
open=false;
}
#Override
public void windowIconified(WindowEvent e) {
}
#Override
public void windowDeiconified(WindowEvent e) {
}
#Override
public void windowActivated(WindowEvent e) {
}
#Override
public void windowDeactivated(WindowEvent e) {
}
});
sentMsg();
receivedMsg();
msgBox();
sendBtn();
save();
frame.add(panel);
frame.setVisible(true);
}
public static void sentMsg() {
sent = new JTextArea(15, 20);
sent.setText("Sent" + "\n");
sent.setLineWrap(true);
sent.setEditable(false);
JScrollPane pane = new JScrollPane(sent, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
panel.add(pane);
}
public static void receivedMsg() {
received = new JTextArea(15, 20);
received.setText("Received" + "\n");
received.setEditable(false);
received.setLineWrap(true);
JScrollPane pane1 = new JScrollPane(received, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
panel.add(pane1);
}
public static void msgBox() {
newMsg = new JTextArea(1, 15);
newMsg.setText("");
newMsg.setLineWrap(true);
JScrollPane pane2 = new JScrollPane(newMsg, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
panel.add(pane2);
}
public static void sendBtn() {
sendButton = new JButton();
sendButton.setText("Send!");
/*sendButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
msg = newMsg.getText();
newMsg.setText(null);
SwingWorker worker = new SwingWorker() {
#Override
protected Object doInBackground() throws Exception {
sockets.sendMsg(msg);
return null;
}
};
worker.execute();
try {
sockets.sendMsg(msg);
} catch (IOException e1) {
e1.printStackTrace();
}
msg = null;
}
});*/
panel.add(sendButton);
}
public static void save(){
JButton save = new JButton();
save.setText("Save Conversation");
save.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
saveToFile save = new saveToFile();
}
});
panel.add(save);
}
}

simple client server chat application not working

I am trying to a simple client server chat application using Stream sockets and Swing. But it is not working as it should. Apparently the server just waits for connection and does not proceed.
I have three java files, Server.java , Client.java and ChatApp.java
Server.java
package com.htpj.networkingChatApp;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Server extends JFrame {
private static final long serialVersionUID = 1L;
private JTextArea displayArea;
private JTextField messageEnterField;
private ServerSocket server;
private Socket connectionSocket;
private ObjectInputStream input;
private ObjectOutputStream output;
private int counter = 1;
protected void serverGui() {
messageEnterField = new JTextField();
setMessageEnterFieldEditable(false);
messageEnterField.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
sendDataToClient(e.getActionCommand());
}
});
add(messageEnterField, BorderLayout.SOUTH);
displayArea = new JTextArea();
add(new JScrollPane(displayArea), BorderLayout.CENTER);
displayArea.setEditable(false); // display area is never editable
setSize(500, 500);
setLocationRelativeTo(null);
setTitle("Chat Server");
setVisible(true);
}
protected void runServer() {
try {
server = new ServerSocket(2000, 100);
while (true) {
try {
waitForConnection(); // wait for a connection
getStreams(); // get input and output streams
processConnection(); // process connections
} catch (EOFException e) {
displayMessage("\n server terminated the connection");
} finally {
closeConnection();
++counter;
}
}
} catch (IOException e) {
e.printStackTrace();
}
} // ENDOF method runServer
private void waitForConnection() {
try {
displayMessage("Waiting for Connection\n");
connectionSocket = server.accept();
displayMessage("Connection" + counter + "received from: " + connectionSocket.getInetAddress() + "port: "
+ connectionSocket.getPort());
} catch (IOException e) {
e.printStackTrace();
}
} // ENDOF method waitForConnection
private void getStreams() throws IOException {
output = new ObjectOutputStream(connectionSocket.getOutputStream());
output.flush(); // flush output buffer to send header information
input = new ObjectInputStream(connectionSocket.getInputStream());
displayMessage("\n Got I/O Streams \n");
} // ENDOF getStreams method
private void processConnection() throws IOException {
String message = null;
sendDataToClient("Connection Successful \n");
setMessageEnterFieldEditable(true); // enable server to type message
do {
try {
message = (String) input.readObject();
displayMessage("\n" + message);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
} while (!message.equals("CLIENT >> TERMINATE"));
} // ENDOF processConnection method
private void closeConnection() {
displayMessage("\n closing connection \n");
setMessageEnterFieldEditable(false);
try {
output.close();
input.close();
connectionSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
} // ENDOF closeConnection method
private void sendDataToClient(String messageFromServer) {
try {
output.writeObject("SERVER>> " + messageFromServer);
output.flush(); // flush output to client
} catch (IOException e) {
e.printStackTrace();
}
} // ENDOF sendDataToClient method
private void displayMessage(String showMessage) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
displayArea.append(showMessage);
}
});
} // ENDOF method displayMessage
private void setMessageEnterFieldEditable(final boolean isEditable) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
messageEnterField.setEditable(isEditable);
}
});
}
} // ENDOF class server
Client.java
package com.htpj.networkingChatApp;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Client extends JFrame {
private static final long serialVersionUID = 1L;
private JTextField messageEnterField;
private JTextArea displayArea;
private String chatHost;
private Socket clientSocket;
private ObjectInputStream input;
private ObjectOutputStream output;
private String message = "";
public Client(String host) {
this.chatHost = host;
}
protected void clientGui() {
messageEnterField = new JTextField();
setMessageEnterFieldEditable(false);
messageEnterField.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
sendDataToServer(e.getActionCommand());
}
});
add(messageEnterField, BorderLayout.SOUTH);
displayArea = new JTextArea();
add(new JScrollPane(displayArea), BorderLayout.CENTER);
displayArea.setEditable(false);
setTitle("Chat Client");
setSize(500, 500);
setLocationRelativeTo(null);
setVisible(true);
} // END OF clientGui method
// connect to the server and process message from server
protected void runClient() throws UnknownHostException, IOException, ClassNotFoundException {
// connect to server, get Streams, process connection
try {
connectToServer();
getStreams();
processConnection();
} catch (EOFException e) {
displayMessage("\n client closed the connection");
} finally {
closeConnection();
}
}
private void connectToServer() throws UnknownHostException, IOException {
displayMessage("Attempting Connection to Server: \n");
clientSocket = new Socket(InetAddress.getByName(chatHost), 2000);
displayMessage(
"Connected to: " + clientSocket.getInetAddress().getHostName() + "on Port : " + clientSocket.getPort());
} // END OF method connectToServer
private void getStreams() throws IOException {
output = new ObjectOutputStream(clientSocket.getOutputStream());
output.flush();
input = new ObjectInputStream(clientSocket.getInputStream());
displayMessage("\n Got I/O stream \n ");
} // END OF getStreams method
private void processConnection() throws ClassNotFoundException, IOException {
displayMessage("\n connected to server\n");
setMessageEnterFieldEditable(true);
do {
message = (String) input.readObject();
displayMessage("\n" + message);
} while (!message.equals("SERVER>> TERMINATE"));
} // end of processConnection method
private void closeConnection() throws IOException {
displayMessage("\n closing connection ");
input.close();
output.close();
clientSocket.close();
setMessageEnterFieldEditable(false);
} // end of closeConnection method
private void displayMessage(final String messageToShow) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
displayArea.append(messageToShow);
}
});
} // end of displayMessage method
private void sendDataToServer(String messageToServer) {
try {
output.writeObject(messageToServer);
output.flush();
} catch (IOException e) {
e.printStackTrace();
}
} // end of sendDataToServer method
private void setMessageEnterFieldEditable(final boolean isEditable) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
messageEnterField.setEditable(isEditable);
}
});
}
}
ChatApp.java
package com.htpj.networkingChatApp;
import java.io.IOException;
public class ChatApp{
public static void main(String[] args) {
Server chatServer = new Server();
Client chatClient = new Client("127.0.0.1");
chatServer.serverGui();
chatClient.clientGui();
chatServer.runServer();
try {
chatClient.runClient();
} catch (ClassNotFoundException | IOException e) {
e.printStackTrace();
}
}
}

issue in sending the socket output to GUI

I wrote this simple multi threaded chatroom, and I am trying to send the client/server output to GUI to display it in chatroom text area but I get null pointer exception at the following line:
output.write(line + "\n");
here is the full code for GUI:
import java.awt.*;
import javax.swing.*;
import javax.swing.JTextField;
import javax.swing.JFrame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.io.IOException;
import javax.swing.JButton;
import java.io.Writer;
public class GUI {
private JFrame frame;
private JButton btnSend, btnConnect;
private JTextArea txtChat;
private JTextField fldText, fldName;
private JList clientList;
private DefaultListModel listModel;
private JScrollPane sc, scClients;
private JPanel jpS2All, jpS2Client, jpS2Text;
private String Name;
private JLabel lblErr;
private Writer output;
public GUI(String Name, Writer output) {
this.Name = Name;
this.output = output;
}
public GUI() {
}
class handler implements ActionListener, MouseListener {
handler(String Name) {
}
handler() {
}
#Override
public void actionPerformed(ActionEvent e) {
clients(); //it seems this line made the error because it creates the
listModel.addElement(Name);//gui and sends the output to textSend actionlistener
//to display it in gui
//while the output is empty, right?
//is there any way to handle this?
}
#Override
public void mouseClicked(MouseEvent e) {
fldName.setText("");
}
#Override
public void mousePressed(MouseEvent e) {
}
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
}
#Override
public void mouseExited(MouseEvent e) {
}
} //end of handler
class textSend implements ActionListener {
textSend(String Name, Writer output) {
}
#Override
public void actionPerformed(ActionEvent e) {
String line = fldText.getText();
try {
output.write(line + "\n"); // the null exception error shows the
output.flush(); // error source at this line!
} catch (IOException ioe) {
txtChat.append("Other party hung up!");
}
String contenet = Name + ":" + output;
txtChat.append(contenet);
fldText.setText("");
}
}//end of textSend
public void creatServer() {
frame = new JFrame("enter");
frame.setBounds(50, 50, 300, 200);
btnConnect = new JButton("connect");
lblErr = new JLabel();
lblErr.setText("");
frame.add(btnConnect, BorderLayout.EAST);
fldName = new JTextField();
fldName.setText("enter your name");
fldName.addMouseListener(new handler());
btnConnect.addActionListener(new handler(getName()));
frame.add(fldName, BorderLayout.CENTER);
frame.setVisible(true);
}
public void clients() { //to create the chatroom GUI
frame = new JFrame("friends");
frame.setBounds(100, 100, 400, 400);
jpS2All = new JPanel();
txtChat = new JTextArea();
txtChat.setRows(25);
txtChat.setColumns(25);
txtChat.setEditable(false);
sc = new JScrollPane(txtChat);
jpS2All.add(sc);
frame.add(jpS2All, BorderLayout.WEST);
jpS2Text = new JPanel();
////////////////////////
fldText = new JTextField();
fldText.setColumns(34);
fldText.setHorizontalAlignment(JTextField.RIGHT);
fldText.addActionListener(new textSend(getName(), output));
jpS2Text.add(fldText);
frame.add(jpS2Text, BorderLayout.SOUTH);
/////////
jpS2Client = new JPanel();
listModel = new DefaultListModel();
clientList = new JList(listModel);
clientList.setFixedCellHeight(14);
clientList.setFixedCellWidth(100);
scClients = new JScrollPane(clientList);
frame.add(jpS2Client.add(scClients), BorderLayout.EAST);
/////////
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
frame.pack();
}//end of clients
public String getName() {
Name = fldName.getText();
return Name;
}
public void appendText(final String message) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
txtChat.append(message);
}
});
}
}
server code:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;
public class server {
public void start() throws IOException {
ServerSocket serverSocket = new ServerSocket(1234);
while (true) {
Socket socket = serverSocket.accept();
ClientThread t = new ClientThread(socket);
t.start();
}
}
public static void main(String[] args) throws IOException {
server server = new server();
server.start();
}
class ClientThread extends Thread {
Socket socket;
InputStream sInput;
OutputStream sOutput;
GUI gui = new GUI();
String Name;
ClientThread(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
try {
BufferedReader sInput
= new BufferedReader(new InputStreamReader(socket.getInputStream()));
Writer sOutput = new OutputStreamWriter(socket.getOutputStream());
Name = gui.getName();
gui = new GUI(Name, sOutput);
try {
String line;
while ((line = sInput.readLine()) != null) {
gui.appendText(line);
}
} catch (IOException ex) {
Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex);
}
} catch (IOException e) {
}
}
}
}
client side:
import java.net.*;
import java.io.*;
import java.util.logging.Level;
import java.util.logging.Logger;
public class client {
private Socket s;
private String Name;
private GUI gui;
private Writer output;
private BufferedReader input;
public void start() {
try {
s = new Socket("127.0.0.1", 1234);
} catch (IOException ex) {
}
try {
input = new BufferedReader(new InputStreamReader(s.getInputStream()));
output = new OutputStreamWriter(s.getOutputStream());
} catch (IOException eIO) {
}
Name = gui.getName();
new GUI(Name, output);
new ListenFromServer().start();
}
public static void main(String[] args) {
client cl = new client();
GUI gui = new GUI();
gui.creatServer();
}
class ListenFromServer extends Thread {
public void run() {
try {
String line;
while ((line = input.readLine()) != null) {
gui.appendText(line);
}
} catch (IOException ex) {
Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
}
I know my question is a bit cumbersome but I really appreciate to help me handle this issue!

I am looking at your code and it is obvious that output is null when you attempt output.write(line + "\n"); Therefore I went and looked for the possible path of execution that could leave output un-initialized. This is where debugging comes in very handy.
Here is your execution path:
In your main method of client you create a new GUI and then call gui.creatServer();
public static void main(String[] args) {
client cl = new client();
GUI gui = new GUI();
gui.creatServer();
}
output has not been assigned and is still null
in the creatServer(); method you have this line:
fldName.addMouseListener(new handler());
which the actionPerformed method of handler calls the clients(); method which has the line:
fldText.addActionListener(new textSend(getName(), output));
note output is still null
(now your textSend class doesn't even do anything inside the constructor but that aside even if it did you are still using the output variable from the GUI class)
you have the actionPerformed method in the textSend class that has the line:
output.write(line + "\n");
Without ever initializing output it is still null, which gives you the NullPointer
Please see What is a NullPointerException, and how do I fix it? as #markspace linked in the comments. In addition you should really learn how to debug small programs.
See the following links:
http://ericlippert.com/2014/03/05/how-to-debug-small-programs/
http://blogs.msdn.com/b/smallbasic/archive/2012/10/09/how-to-debug-small-basic-programs.aspx
Again in addition, consider using Anonymous classes to ease up on those lines of code, which also makes the code easier to debug and more readable.
One last thought, remember to use standard Naming Conventions for the language you are using. your code currently has a lot of incorrect lowercase classes and some uppercase methods/properties.

the error message shows that one of the variable used in the expression was null. This may be either output or line.
As chancea already mentioned, you are calling the GUI() constructor with no arguments, so the output field is not initialized. You should remove the constructor with no arguments when you have no way to initialize the output field in it and only leave the one with arguments.

add jbutton at runtime

I am building an application on Socket programming in swing in which server listens for clients and if a client is connected I want
A button should be added for each client if connected on server screen
Add a listener on each button.For example add Send Message function for each client
I have created a thread in server which listens for client connections but I can not add jbutton at runtime.
Please reply.

Is that what you need ? :
import javax.swing.*;
import java.awt.event.*;
public class NewButtonOnRunTime {
static JPanel panel;
static JFrame frame;
public static void main(String[] args){
javax.swing.SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
frame = new JFrame("Add Buttons");
JButton button = new JButton("Simulate new Client");
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
JButton jb = new JButton("A new Client");
jb.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog(null, "This is an button action");
}
});
panel.add(jb);
frame.revalidate();
}
});
panel = new JPanel();
panel.add(button);
frame.add(panel);
frame.setSize(400, 400);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
});
}
}

Assuming you already have some kind of isConnected bool,
if(isConnected){
JButton runTimeButton = new JButton();
runTimeButton.addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
//do all the things you need to do in here,
//alternatively, define this inner class somewhere else and pass in
// an instance of it
}
});
frame.add(runTimeButton);
}

Based on ServerSocket communication in java (i.e. TCP), if a client is connected to the server with a particular port say 5555, no other clients will not be able to connect to the server with the same port at the same time because the port is already in use. So, each client should be using different port if you want to get simultaneous communication with the clients.
Look at this sample code, it adds JButton at runtime when a new client is connected :
(run client code and server code in separate machine connected together)
Server code
package com.test.socket;
import java.awt.FlowLayout;
import java.awt.Toolkit;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.HashMap;
import java.util.Map;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextArea;
public class ServerFrame extends JFrame {
private Map<Integer, SocketVO> serverSocketMap;
private int startingPort = 5555;
public ServerFrame() {
}
public ServerFrame(String title) {
super(title);
setSize(Toolkit.getDefaultToolkit().getScreenSize());
setLayout(new FlowLayout());
initComponents();
serverSocketMap = new HashMap<Integer, SocketVO>();
keepStartServerSocket();
setVisible(true);
}
private JTextArea area = null;
private void initComponents() {
area = new JTextArea(20, 20);
add(area);
// addDynamicButton();
}
private void addDynamicButton(final int port) {
JButton button = new JButton("Client on " + port + " port");
add(button);
button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent event) {
Socket socket = serverSocketMap.get(port).getSocket();
try {
String content = area.getText();
socket.getOutputStream().write(content.getBytes());
System.out.println("seding text area content to " + port);
System.out.println(content);
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
class SocketVO {
private ServerSocket serverSocket;
private Socket socket;
public ServerSocket getServerSocket() {
return serverSocket;
}
public void setServerSocket(ServerSocket serverSocket) {
this.serverSocket = serverSocket;
}
public Socket getSocket() {
return socket;
}
public void setSocket(Socket socket) {
this.socket = socket;
}
}
private void keepStartServerSocket() {
new Thread(new Runnable() {
#Override
public void run() {
while (true) {
System.out.println("waiting for a client at port "
+ startingPort);
openServerSocket(startingPort);
startingPort++;
}
}
}).start();
}
private void openServerSocket(final int port) {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(port);
final Socket socket = serverSocket.accept();
SocketVO socketVO = new SocketVO();
socketVO.setServerSocket(serverSocket);
socketVO.setSocket(socket);
serverSocketMap.put(port, socketVO);
addDynamicButton(port);
checkForCosing(port, socket);
} catch (IOException e) {
e.printStackTrace();
}
}
private void checkForCosing(final int port, final Socket socket) {
new Thread(new Runnable() {
#Override
public void run() {
InputStream inputStream = null;
try {
inputStream = socket.getInputStream();
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
byte[] b = new byte[1024];
int read = 0;
try {
StringBuilder builder = new StringBuilder();
while ((read = inputStream.read(b)) != -1) {
builder.append(new String(b));
}
if (builder.toString().equals("close")) {
closeServerSocket(port);
System.out.println("server port " + port + " closed");
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}).start();
}
/**
* the method to close corresponding sockets
*
* #param port
*/
private void closeServerSocket(int port) {
Socket socket = serverSocketMap.get(port).getSocket();
ServerSocket serverSocket = serverSocketMap.get(port).getServerSocket();
try {
socket.close();
serverSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
new ServerFrame("Server Socket Frame");
}
}
Client code :
package com.test.socket;
import java.io.IOException;
import java.io.InputStream;
import java.net.Socket;
import java.net.UnknownHostException;
public class Client {
private int startingPort = 5550;
private void bindToServer() {
while(true) {
try {
Socket socket = new Socket("127.0.0.1", startingPort);
InputStream inputStream = null;
try {
inputStream = socket.getInputStream();
} catch (IOException e1) {
e1.printStackTrace();
}
byte[] b = new byte[1024];
int read = 0;
try {
StringBuilder builder = new StringBuilder();
while((read = inputStream.read(b)) != -1) {
builder.append(new String(b));
}
System.out.println("message from server : "+builder);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
startingPort++;
}
if (startingPort == 5580) {
}
}
}
public static void main(String[] args) {
new Client().bindToServer();
}
}

As per your last comment:
I have tested the program with two clients. The server is connected to two clients successfully. But buttons are not added at runtime for each client.
You are able to connect with multiple client and you have added a button also but it's not visible on the server.
Calling validate() again on JFrame will solve your problem after adding new JButton.

public class Test extends JFrame {
private JButton field[];
public JButton[] getField() {
return field;
}
public void test(int n) {
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(0, 1));
field = new JButton[n];
for (int i = 0; i < field.length; i++) {
field[i] = new JButton("" + i + "");
field[i].addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("clicked button");
}
});
panel.add(field[i]);
}
add(panel);
}
public static void main(String[] args) {
Test test = new Test();
test.setSize(300, 300);
test.setVisible(true);
test.setLocationRelativeTo(null);
test.test(5);
}
}

How do I select which stream to close out of multiple streams?

I didn't realize until now that my disconnect button on my program was failing. If I have 3 clients up, and any of them click disconnect, then only the last client gets disconnected. How do I select which instance I need to close? If out of the 3 users I want to remove the first one..
server:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;
public class Server {
private Set<Socket> sockets = new HashSet<Socket>();
private Set<String> names = new HashSet<String>();
private Socket sock;
private static int port;
private Calendar cal = Calendar.getInstance();
private SimpleDateFormat date = new SimpleDateFormat("dd/mm/yyyy hh:mm:ss");
public Server(int input) {
port = input;
}
public static void main(String[] args) {
/*
* user defines port number, server initialized
*/
System.out.println("enter a port");
Scanner input = new Scanner(System.in);
port = input.nextInt();
new Server(port).go();
input.close();
}
public void go() {
try {
/*
* wait for connections, add connections to Set, setup streams per
* connection in new threads
*/
System.out.println("waiting for connetion");
#SuppressWarnings("resource")
ServerSocket serverSocket = new ServerSocket(port);
while (true) {
sock = serverSocket.accept();
sockets.add(sock);
Thread t = new Thread(new ClientHandler(sock));
t.start();
System.out.println("connected: " + sock.getInetAddress());
}
} catch (IOException ex) {
ex.printStackTrace();
System.out.println("server setup failed");
}
}
class ClientHandler implements Runnable {
/*
* client handler sets up streams
*/
private BufferedReader in;
private PrintWriter out;
private String name;
public ClientHandler(Socket sock) {
try {
in = new BufferedReader(new InputStreamReader(
sock.getInputStream()));
out = new PrintWriter(sock.getOutputStream(), true);
} catch (IOException e) {
e.printStackTrace();
System.out.println("stream setup failed");
}
}
#Override
public void run() {
/*
* First check if user exists, if true than close connection and
* warn user about name. Then relay message to all clients, if user
* DC's than remove the socket from the Set
*/
String message;
try {
name = in.readLine();
if (names.contains(name)) {
System.out.println("duplicate name detected, removing..");
out.println("choose new name and reconnect: "
+ sock.getInetAddress());
sock.close();
sockets.remove(sock);
} else {
names.add(name);
System.out.println("Users active: " + names);
shout("user: " + name + " connected!" + " from "
+ sock.getInetAddress());
}
while ((message = in.readLine()) != null) {
/*
* call method which checks if user tries to enter a command
* such as /laugh or /roll, otherwise relay the message to
* all clients
*/
swich(message);
}
} catch (IOException ex) {
System.out.println("user disconnected: " + name + " "
+ sock.getInetAddress());
shout("user disconnected: " + name + " "
+ sock.getInetAddress());
names.remove(name);
remove(sock);
}
}
public synchronized void shout(String message) {
// send message to all clients in Set
for (Socket sock : sockets) {
try {
PrintWriter writer = new PrintWriter(
sock.getOutputStream(), true);
writer.println(date.format(cal.getTime()) + " " + message
+ "\n");
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void swich(String message) throws IOException {
// check if user calls a chat command
// otherwise shout message to all clients
switch (message) {
case "/disconnect":
out.println("disconnected");
remove(sock);
break;
case "/laugh":
String[] laughs = { "HahHA!", "HAHAAH!!!!", "haaaaa!!!",
"hohohoohohahhaa!!!", "huehuehue!" };
shout(name + " " + laughs[(int) (Math.random() * 5)]);
break;
case "/roll":
shout(name + " rolls "
+ Integer.toString((int) ((Math.random() * 6) + 1)));
break;
case "kirby!":
shout("(>'-')> <('-'<) ^(' - ')^ <('-'<) (>'-')>");
break;
default:
shout(message);
System.out.println("client says : "
+ date.format(cal.getTime()) + message);
}
}
}
public void remove(Socket soc) {
try {
soc.close();
sockets.remove(soc);
} catch (IOException e) {
e.printStackTrace();
}
}
}
client:
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Client {
private JTextArea tArea;
private JTextField tField;
private JTextField portText;
private JTextField hostText;
private BufferedReader in;
private Socket sock;
private static PrintWriter out;
private static String name;
private String host;
private String port;
public static void main(String[] args) {
System.out.println("Enter username");
Scanner input = new Scanner(System.in);
name = input.nextLine();
input.close();
new Client().go();
}
public void go() {
/*
* build gui
*/
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JFrame frame = new JFrame("hakobChat");
JPanel topPanel = new JPanel();
JLabel portLabel = new JLabel("port");
JLabel hostLabel = new JLabel("host");
portText = new JTextField(6);
hostText = new JTextField(12);
JButton connect = new JButton("connect");
connect.addActionListener(new connectListener());
JButton disconnect = new JButton("disconnect");
disconnect.addActionListener(new disconnectListener());
tField = new JTextField(30);
tField.addActionListener(new sendListener());
tArea = new JTextArea(30, 50);
tArea.setEditable(false);
tArea.setLineWrap(true);
JScrollPane tScroll = new JScrollPane(tArea,
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
JButton button = new JButton("send");
button.addActionListener(new sendListener());
topPanel.add(hostLabel);
topPanel.add(hostText);
topPanel.add(portLabel);
topPanel.add(portText);
topPanel.add(connect);
topPanel.add(disconnect);
frame.setSize(300, 500);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(topPanel, BorderLayout.NORTH);
frame.getContentPane().add(tScroll, BorderLayout.CENTER);
frame.getContentPane().add(tField, BorderLayout.SOUTH);
frame.getContentPane().add(button, BorderLayout.EAST);
frame.pack();
}
});
}
public void setupNetwork(String host, int port) {
/*
* setup in and out stream send user name to server to check if
* duplicate start thread for incoming messages
*/
try {
sock = new Socket(host, port);
in = new BufferedReader(
new InputStreamReader(sock.getInputStream()));
out = new PrintWriter(sock.getOutputStream(), true);
out.println(name);
showMessage("Connected!");
showMessage("enter /laugh or /roll or kirby! for some fun!");
Thread t = new Thread(new IncomingReader());
t.start();
} catch (IOException ex) {
ex.printStackTrace();
showMessage("please enter valid network");
}
}
class IncomingReader implements Runnable {
// receive messages from server
public void run() {
try {
String message = null;
while ((message = in.readLine()) != null) {
showMessage(message + "\n");
}
} catch (Exception e) {
e.printStackTrace();
showMessage("choose new name and reconnect please");
}
}
}
public synchronized void sendMessage(String message) {
try {
switch (message) {
case "/laugh":
out.println("/laugh");
break;
case "/roll":
out.println("/roll");
break;
case "kirby!":
out.println("kirby!");
break;
default:
out.println("(" + name + ")" + ": " + message);
}
} catch (Exception e) {
e.printStackTrace();
System.out.println("fail send message");
}
}
public void showMessage(final String message) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
tArea.append(message + "\n");
tArea.setCaretPosition(tArea.getDocument().getLength());
// SetCaretPosition forces autos scroll
}
});
}
class sendListener implements ActionListener {
// listens for user to trying to send a message
public void actionPerformed(ActionEvent ev) {
sendMessage(tField.getText());
tField.setText("");
}
}
class disconnectListener implements ActionListener {
public void actionPerformed(ActionEvent ev) {
try {
out.println("/disconnect");
} catch (NullPointerException e) {
showMessage("not connected");
}
}
}
class connectListener implements ActionListener {
public void actionPerformed(ActionEvent ev) {
host = hostText.getText();
port = portText.getText();
if (!host.equals("") && !port.equals("") && port.matches("[1-9]+")) {
// make sure user enters valid inputs
// before setting up network
setupNetwork(host, Integer.parseInt(port));
} else {
showMessage("enter valid network credentials");
}
}
}
}
Also, how do I avoid this "#SuppressWarnings("resource")". If I don't have this eclipse provided warning than the serverSocket is underlined yellow.

You need to save a the Socket used for the client inside of the ClientHandler.
You can do this by simply adding a
private Socket sock;
inside of ClientHandler, and adding:
this.sock = sock;
inside of its constructor.
Currently you're using the Socket saved in the server, which will always be the socket of the last client that connected, rather than the Socket belonging to the current client.

This is just a scoping problem. The Socket sock member shouldn't be part of the Server class. It should be part of the ClientHandler class. One per client.