using singleton for creating listener object not working

using singleton for creating listener object not working

i am using a singleton that for some reason is not working, can't figure
out why
private static ConnectionUtility instance;
public static ConnectionUtility getInstance() {
if(instance == null){
instance = new ConnectionUtility();
}
return instance;
}
in the code shown above, the second time the execution of this code takes
place, instance is not null, an instance has been created already, so on
the second time this code is executed it should go to the return instance
line directly and skip the instance = new ConnectionUtility() line.
however on second iteration it will try to create another instance of the
ConnectionUtility object when one already exists. why is it doing this?
how to fix this problem?
full code posted below: for 2 classes ConnectionUtility and MultiThreader
public class ConnectionUtility extends javax.swing.JFrame
implements MultiThreader.OnSendResultListener {
String outputLine = "";
boolean runner = true;
PrintWriter out;
BufferedReader in;
ServerSocket serversocket;
static Socket socket;
boolean startServer = true;
public static String displayString = "";
private static ConnectionUtility instance;
static int counter = 0;
public static ConnectionUtility getInstance() {
if(instance == null){
instance = new ConnectionUtility();
}
return instance;
}
private ConnectionUtility() {
initComponents();
this.setVisible(true);
serverRunner();
File fileOne = new File("C:/DBFiles");
if(!fileOne.exists()){
fileOne.mkdir();
}
File fileTwo = new File("C:/DBFilesOut");
if(!fileTwo.exists()){
fileTwo.mkdir();
}
}
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
jLabel1 = new javax.swing.JLabel();
jScrollPane1 = new javax.swing.JScrollPane();
jTextArea1 = new javax.swing.JTextArea();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
jLabel1.setFont(new java.awt.Font("MS UI Gothic", 0, 36)); // NOI18N
jLabel1.setText("TankInspectionSystem");
jTextArea1.setColumns(20);
jTextArea1.setRows(5);
jScrollPane1.setViewportView(jTextArea1);
javax.swing.GroupLayout layout = new
javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(72, 72, 72)
.addComponent(jLabel1)
.addContainerGap(76, Short.MAX_VALUE))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING,
layout.createSequentialGroup()
.addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE,
Short.MAX_VALUE)
.addComponent(jScrollPane1,
javax.swing.GroupLayout.PREFERRED_SIZE, 383,
javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE,
Short.MAX_VALUE))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(37, 37, 37)
.addComponent(jLabel1)
.addGap(34, 34, 34)
.addComponent(jScrollPane1,
javax.swing.GroupLayout.PREFERRED_SIZE, 179,
javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap(37, Short.MAX_VALUE))
);
pack();
}// </editor-fold>
private javax.swing.JLabel jLabel1;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JTextArea jTextArea1;
// End of variables declaration
public void serverRunner(){
runner = true;
try {
serversocket = new ServerSocket(6789, 100);
System.out.println();
} catch (IOException ex) {
Logger.getLogger(ConnectionUtility.class.getName()).log(Level.SEVERE,
null, ex);
}
while(runner){
try {
socket = serversocket.accept();
addAndDisplayTextToString("new connection, inet socket address >>> " +
socket.getPort());
System.out.println(displayString);
} catch (IOException ex) {
Logger.getLogger(ConnectionUtility.class.getName()).log(Level.SEVERE,
null, ex);
}
// MultiThreader multi = new MultiThreader(socket, this);
MultiThreader multi = new MultiThreader(socket);
Thread t = new Thread(multi);
t.start();
} // end while runner loop
} // end serverRunner method
public static void addAndDisplayTextToString(String setString){
StringBuilder stb = new StringBuilder(displayString);
setString = setString + "\n";
if(stb.toString() == ""){
stb.append(setString);
}else if(stb.toString() != ""){
stb.insert(0, setString);
}
int counter = 0;
for(int i = 0; i < stb.length(); i++){
if(stb.substring(i, i + 1).equals("\n")){
counter++;
}
}
// get the last index of "\n"
int lastIndex = stb.lastIndexOf("\n");
int maximum = 4;
if(counter >= maximum){
stb.delete(lastIndex, stb.length());
System.out.println();
}
displayString = stb.toString();
}
@Override
public void onStringResult(String transferString) {
addAndDisplayTextToString(transferString);
jTextArea1.setText(displayString);
System.out.println("RETURNED TRING " + transferString);
}
} // class ConnectionUtility



public class MultiThreader implements Runnable {
private Socket socket;
public int fileSizeFromClient;
FileOutputStream fos = null;
BufferedInputStream bis = null;
BufferedOutputStream bos = null;
DataInputStream dis = null;
DataOutputStream dos = null;
ScheduledThreadPoolExecutor stpe;
private OnSendResultListener listener;
public MultiThreader(Socket s) {
// public MultiThreader(Socket s, OnSendResultListener resultListener){
socket = s;
stpe = new ScheduledThreadPoolExecutor(5);
listener = ConnectionUtility.getInstance();
// listener = resultListener;
}
@Override
public void run() {
long serialNumber = 0;
int bufferSize = 0;
// get input streams
try {
bis = new BufferedInputStream(socket.getInputStream());
dis = new DataInputStream(bis);
} catch (IOException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
sendStatus("New connection strarted");
// read in streams from server
try {
fileSizeFromClient = dis.readInt();
sendStatus("File size from client " + fileSizeFromClient);
serialNumber = dis.readLong();
sendStatus("Serial mumber from client " + serialNumber);
} catch (IOException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
try {
bufferSize = socket.getReceiveBufferSize();
sendStatus("Buffer size " + bufferSize);
} catch (SocketException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
String serialString = String.valueOf(serialNumber);
File fileDirectory = new File("C:" + File.separator + "DOWNLOAD" +
File.separator + serialNumber + File.separator);
fileDirectory.mkdir();
File file = new File("C:" + File.separator + "DOWNLOAD" +
File.separator + serialNumber + File.separator + "JISSend.pdf");
try {
file.createNewFile();
} catch (IOException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
try {
fos = new FileOutputStream(file);
bos = new BufferedOutputStream(fos);
dos = new DataOutputStream(bos);
} catch (FileNotFoundException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
int count = 0;
byte[] buffer = new byte[fileSizeFromClient];
try {
int totalBytesRead = 0;
while(totalBytesRead < fileSizeFromClient){
int bytesRemaining = fileSizeFromClient - totalBytesRead;
int bytesRead = dis.read(buffer, 0, (int)Math.min(buffer.length,
bytesRemaining));
if(bytesRead == -1){
break;
}else{
dos.write(buffer, 0, bytesRead);
totalBytesRead += bytesRead;
}
}
} catch (IOException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
try {
dos = new DataOutputStream(socket.getOutputStream());
} catch (IOException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
stpe.schedule(new CompareFiles(), 0, TimeUnit.SECONDS);
stpe.schedule(new CloseResources(), 2, TimeUnit.SECONDS);
} // end run method
public class CompareFiles implements Runnable {
@Override
public void run() {
int returnInt = 0;
FileInputStream fis = null;
File file = new File("C:/DOWNLOAD/JISSend.pdf");
try {
fis = new FileInputStream(file);
} catch (FileNotFoundException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
int fileLength = (int) file.length();
sendStatus("Size of database file sent " + fileLength);
if(fileLength == fileSizeFromClient){
sendStatus("File sent to server, Successful");
returnInt = 1;
}else if(fileLength != fileSizeFromClient){
sendStatus("ERROR, file send failed");
returnInt = 2;
}
try {
dos.writeInt(returnInt);
} catch (IOException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
} // end run method
} // end of class comparefiles
public class CloseResources implements Runnable {
@Override
public void run() {
try {
fos.flush();
bis.close();
bos.close();
dis.close();
dos.close();
socket.close();
} catch (IOException ex) {
Logger.getLogger(MultiThreader.class.getName()).log(Level.SEVERE,
null, ex);
}
} // end run method
} // end of class closeResources
public interface OnSendResultListener {
public void onStringResult(String transferString);
}
public void sendStatus(String status){
listener.onStringResult(status);
}
} // end class mulitthreader