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Threads. Stopping Server

Recently I was doing multithreaded chat application. Now I am struggling with server. I am trying to stop the server by introducing new field online, but it doesn't help.
import view.ChatHub;
import java.io.IOException;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Set;
import java.util.HashSet;
import java.util.Scanner;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ChatServer extends Thread {
// All client names, so we can check for duplicates upon registration.
private static Set<String> names = new HashSet<>();
// The set of all the print writers for all the clients, used for broadcast.
private static Set<PrintWriter> writers = new HashSet<>();
private ChatHub frame;
private int port;
private boolean online;
private ExecutorService pool;
public ChatServer(int port) throws IOException {
System.out.println("The chat server is running...");
this.frame = new ChatHub(this);
this.port = port;
this.online = true;
this.pool = Executors.newFixedThreadPool(500);
this.start();
}
#Override
public void run() {
while (this.online) {
try (ServerSocket listener = new ServerSocket(this.port)) {
this.pool.execute(new Handler(listener.accept(), this.names, this.writers));
} catch (IOException e) {
e.printStackTrace();
}
}
}
public void stopChatServer() {
this.pool.shutdown();
this.online = false;
}
public Set<String> getNames() {
return this.names;
}
public Set<PrintWriter> getWriters() {
return this.getWriters();
}
public ChatHub getFrame() {
return this.frame;
}
public int getPort() {
return this.port;
}
}
Here I am trying to close the server:
import Client.ChatClient;
import Server.ChatServer;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
public class ChatHub extends JFrame{
JTextField textField;
JTextArea messageArea;
public ChatHub(ChatServer server) {
new JFrame("Chatter");
this.textField = new JTextField(50);
this.messageArea = new JTextArea(16,50);
this.textField.setEditable(true);
this.messageArea.setEditable(false);
this.getContentPane().add(this.textField, BorderLayout.SOUTH);
this.getContentPane().add(new JScrollPane(this.messageArea), BorderLayout.CENTER);
this.pack();
// this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent we) {
server.stopChatServer();
}
});
this.setVisible(true);
}
public void appendMessage(String line) {
messageArea.append(line + "\n");
}
public JTextField getTextField() {
return this.textField;
}
public JTextArea getMessageArea() {
return this.messageArea;
}
public void nameAccepted(String line) {
this.setTitle("Chatter - " + line.substring(13));
textField.setEditable(true);
}
}
Also I tried to have method run with while just printing some String. But when it left run method the program was still working. Any suggestions? Thanks in advance.
Also I tried to implement run() as the following:
#Override
public void run() {
while (this.online) {
System.out.println("Some String");
}
System.out.println(this.isAlive() + "\n");
}
And it does output true in the end.

Maybe you have another problem here (Swing Related):
Your new JFrame("Chatter") just creates a new JFrame and does nothing with it. You have to call super("Chatter"); to call the super constructor
Try
this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE)

Have you tried to declare your online property as volatile?
private volatile boolean online = true;
If you do not declare a property as volatile, the JIT compiler can assume that your boolean property will not be changed by another thread. So it may optimize your run method to
public void run() {
if (!online)
return;
while(true) {
try(/*...*/) {
// ...
} catch(/*...*/) {
// ...
}
}
}

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.

Java: Create text window to display console text

I'm looking to create a seperate window in my java program to basically display the things that I print using println(). It would be nice to have some way of making certain text read and/or bold if it starts with "error:". Is there an easy or straight forward way to doing this?

A simple way would be to write a function that takes a String as an argument and then 1) prints to console using System.out.print*(), followed by printing or copying over text to that window's JTextField, or a constructor, or whatever method you are using to print text in that window, i.e.:
public method printAndCopyText(String text) {
System.out.println(text);
otherWindowObject.getTextFieldObject().setText(text);
}

Here is a sample
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.io.PrintStream;
import java.util.List;
import java.util.Scanner;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextPane;
import javax.swing.SwingWorker;
public class JConsole {
public static void main(String[] args) throws IOException {
JFrame frame = new JFrame("JConsole");
JTextPane jta = new JTextPane();
JButton button = new JButton("Run");
frame.setLayout(new BorderLayout());
frame.add(button,BorderLayout.NORTH);
frame.add(jta,BorderLayout.CENTER);
button.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent e) {
new SwingWorker<Void, Object>(){
#Override
protected Void doInBackground() throws Exception {
outputTest("inner");
return null;
}}.execute();
}});
frame.setSize(400, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
console(jta);
}
public static void outputTest(String msg){
for(int i=0;i<10;i++){
System.out.println(i+" "+msg);
try {
Thread.sleep(500);
} catch (InterruptedException ex) {
ex.printStackTrace();
}
}
}
public static void console(final JTextPane area) throws IOException {
area.setContentType("text/html");
final PipedInputStream outPipe = new PipedInputStream();
System.setOut(new PrintStream(new PipedOutputStream(outPipe), true));
new SwingWorker<Void, String>() {
#Override
protected Void doInBackground() throws Exception {
Scanner s = new Scanner(outPipe);
while (s.hasNextLine()){
String line = s.nextLine();
publish(line + "\n");
}
return null;
}
#Override
protected void process(List<String> chunks) {
for (String line : chunks){
area.setText("<font size=\"3\" color=\"red\">"+line+"</font>");
}
}
}.execute();
}
}

Unable to load a saved JButton

I'm making a program that is saving an array of JButtons to a file .btn. here is the code that is being saved:
package avtech.software.compunav;
import java.io.File;
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import javax.swing.JButton;
public class Buttons implements Serializable {
public static Button[] buttons = new Button[15];
public Buttons() {
for (int i = 0; i < buttons.length; i++) {
buttons[i] = new Button();
buttons[i].setText("Unassigned");
}
}
public JButton[] getButtons() {
return buttons;
}
public JButton getButton(int index) {
return buttons[index];
}
public void setButtonText(String txt, int index) {
buttons[index].setText(txt);
}
public void setButtonAction(String action, int index) {
}
public void save() {
try {
File dir = new File(Core.baseDir + "/bin/buttons.btn");
FileOutputStream fos = new FileOutputStream(dir);
ObjectOutputStream oos = new ObjectOutputStream(fos);
if (dir.exists())
dir.delete();
oos.writeObject(this);
oos.flush();
oos.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
Button is a class that extends JButton, and here is that code:
package avtech.software.compunav;
import java.awt.Desktop;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.IOException;
import javax.swing.JButton;
import CompuNav.main.Dialogs;
public class Button extends JButton implements ActionListener {
private String action = "";
public Button() {
addActionListener(this);
}
public void setAction(String s) {
action = s;
}
#Override
public void actionPerformed(ActionEvent arg0) {
if (action.equals(""))
return;
File file = new File(action);
Desktop dt = Desktop.getDesktop();
try {
dt.open(file);
} catch (IOException e1) {
Dialogs.msg("Could not open " + action);
}
}
}
Basically, the code is saving. there is a file called buttons.btn in the correct directory. The problem is, when I use the load method here:
try {
FileInputStream fis = new FileInputStream(baseDir
+ "/bin/buttons.btn");
ObjectInputStream ois = new ObjectInputStream(fis);
buttonsClass = (Buttons) ois.readObject();
ois.close();
} catch (Exception e) {}
after making a new object of the Buttons and saving it, I get a nullPointerException when trying to call buttonsClass.getButton(0);, implying that the JButtons are not saved when i save the class.
Any reason as to why, and any idea how to fix this?

public static Button[] buttons = new Button[15];
This variable should not be static if you want it to be serialized.

JFrame freeze with different System.in

Anyone can tell me why TryGraphic freeze the JFrame with a scanner in the first main()? If I remove the Scanner or if I execute the code directly, all works. (The original "Try" class obviously do a lot of different stuff. I wrote these classes to make it simple.)
import java.util.Scanner;
public class Try {
public Try(){
}
public static void main(String[] args){
System.out.println("FOO");
String s = new Scanner(System.in).nextLine();
System.out.println(s);
}
}
This is the graphic implementation:
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.util.Scanner;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingWorker;
public class TryGraphic extends JFrame{
/**
*
*/
private static final long serialVersionUID = 7491282237007954227L;
private JButton execute = new JButton("Esegui");
private PipedInputStream inPipe = new PipedInputStream();
private PipedInputStream outPipe = new PipedInputStream();
private JTextField tfIn = new JTextField();
private JTextArea outputArea = new JTextArea();
private PrintWriter inWriter;
public TryGraphic(){
super("TRY");
System.setIn(inPipe);
try {
System.setOut(new PrintStream(new PipedOutputStream(outPipe), true));
inWriter = new PrintWriter(new PipedOutputStream(inPipe), true);
}catch (IOException ioe){
ioe.printStackTrace();
}
tfIn.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent event){
String text = tfIn.getText();
tfIn.setText("");
inWriter.println(text);
}
});
this.add(execute,BorderLayout.SOUTH);
this.add(new JScrollPane(outputArea),BorderLayout.CENTER);
this.add(tfIn, BorderLayout.NORTH);
execute.addActionListener(new ActionListener(){
#Override
public void actionPerformed(ActionEvent e) {
SwingWorker<Void,String> worker = new SwingWorker<Void, String>() {
protected Void doInBackground() throws Exception {
Scanner s = new Scanner(outPipe);
while (s.hasNextLine()) {
String line = s.nextLine();
publish(line);
}
return null;
}
#Override
protected void process(java.util.List<String> chunks) {
for (String line : chunks){
outputArea.append(line+System.lineSeparator());
outputArea.validate();
}
}
};
worker.execute();
Try.main(new String[]{""});
}
});
this.setSize(300,300);
this.setVisible(true);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args){
new TryGraphic();
}
}

You're blocking the GUI Event Dispatch Thread. You need to spawn a separate thread to wait for input so you can keep your GUI responsive.
You're already doing the right thing by creating a SwingWorker to handle I/O in your TryGraphic class. You should do something similar to move the Try.main(new String[]{""}); call off the Event Dispatch Thread, which will keep your JFrame from locking up.