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  • using Object input\ output Streams with files and array list

    - by soad el-hayek
    hi every one .. i'm an it student , and it's time to finish my final project in java , i've faced too many problems , this one i couldn't solve it and i'm really ubset ! :S my code is like this : in Admin class : public ArrayList cos_info = new ArrayList(); public ArrayList cas_info = new ArrayList(); public int cos_count = 0 ; public int cas_count = 0 ; void coustmer_acount() throws FileNotFoundException, IOException{ String add=null; do{ person p = new person() ; cos_info.add(cos_count, p); cos_count ++ ; add =JOptionPane.showInputDialog("Do you want to add more coustmer..\n'y'foryes ..\n 'n'for No .."); } while(add.charAt(0) == 'Y'||add.charAt(0)=='y'); writenew_cos(); // add_acounts(); } void writenew_cos() throws IOException{ ObjectOutputStream aa = new ObjectOutputStream(new FileOutputStream("coustmer.txt")); aa.writeObject(cos_info); JOptionPane.showMessageDialog(null,"Added to file done sucessfuly.."); aa.close(); } in Coustmer class : void read_cos() throws IOException, ClassNotFoundException{ person p1= null ; int array_count = 0; ObjectInputStream d = new ObjectInputStream(new FileInputStrea ("coustmer.txt")); JOptionPane.showMessageDialog(null,d.available() ); for(int i = 0;d.available() == 0;i++){ a.add(array_count,(ArrayList) d.readObject()); array_count++; JOptionPane.showMessageDialog(null,"Haaaaai :D" ); JOptionPane.showMessageDialog(null,array_count ); } d.close(); JOptionPane.showMessageDialog(null,array_count +"1111" ); for(int i = 0 ; i<a.size()&& found!= true ; i++){ count++ ; p1 =(person)a.get(i); user=p1.user; pass = p1.pass; cas_checkpass(); } } it just print JOptionPane.showMessageDialog(null,d.available() ); and having excep. here a.add(array_count,(ArrayList) d.readObject()); p.s : person object from my own class and it's Serializabled

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  • Load/Store Objects in file in Java

    - by brain_damage
    I want to store an object from my class in file, and after that to be able to load the object from this file. But somewhere I am making a mistake(s) and cannot figure out where. May I receive some help? public class GameManagerSystem implements GameManager, Serializable { private static final long serialVersionUID = -5966618586666474164L; HashMap<Game, GameStatus> games; HashMap<Ticket, ArrayList<Object>> baggage; HashSet<Ticket> bookedTickets; Place place; public GameManagerSystem(Place place) { super(); this.games = new HashMap<Game, GameStatus>(); this.baggage = new HashMap<Ticket, ArrayList<Object>>(); this.bookedTickets = new HashSet<Ticket>(); this.place = place; } public static GameManager createManagerSystem(Game at) { return new GameManagerSystem(at); } public boolean store(File f) { try { FileOutputStream fos = new FileOutputStream(f); ObjectOutputStream oos = new ObjectOutputStream(fos); oos.writeObject(games); oos.writeObject(bookedTickets); oos.writeObject(baggage); oos.close(); fos.close(); } catch (IOException ex) { return false; } return true; } public boolean load(File f) { try { FileInputStream fis = new FileInputStream(f); ObjectInputStream ois = new ObjectInputStream(fis); this.games = (HashMap<Game,GameStatus>)ois.readObject(); this.bookedTickets = (HashSet<Ticket>)ois.readObject(); this.baggage = (HashMap<Ticket,ArrayList<Object>>)ois.readObject(); ois.close(); fis.close(); } catch (IOException e) { return false; } catch (ClassNotFoundException e) { return false; } return true; } . . . } public class JUnitDemo { GameManager manager; @Before public void setUp() { manager = GameManagerSystem.createManagerSystem(Place.ENG); } @Test public void testStore() { Game g = new Game(new Date(), Teams.LIONS, Teams.SHARKS); manager.registerGame(g); File file = new File("file.ser"); assertTrue(airport.store(file)); } }

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  • Reading serialised object from file

    - by nico
    Hi everyone. I'm writing a little Java program (it's an ImageJ plugin, but the problem is not specifically ImageJ related) and I have some problem, most probably due to the fact that I never really programmed in Java before... So, I have a Vector of Vectors and I'm trying to save it to a file and read it. The variable is defined as: Vector <Vector <myROI> > ROIs = new Vector <Vector <myROI> >(); where myROI is a class that I previously defined. Now, to write the vector to a file I use: void saveROIs() { SaveDialog save = new SaveDialog("Save ROIs...", imp.getTitle(), ".xroi"); String name = save.getFileName(); if (name == null) return; String dir = save.getDirectory(); try { FileOutputStream fos = new FileOutputStream(dir+name); ObjectOutputStream oos = new ObjectOutputStream(fos); oos.writeObject(ROIs); oos.close(); } catch (Exception e) { IJ.log(e.toString()); } } This correctly generates a binary file containing (I suppose) the object ROIs. Now, I use a very similar code to read the file: void loadROIs() { OpenDialog open = new OpenDialog("Load ROIs...", imp.getTitle(), ".xroi"); String name = open.getFileName(); if (name == null) return; String dir = open.getDirectory(); try { FileInputStream fin = new FileInputStream(dir+name); ObjectInputStream ois = new ObjectInputStream(fin); ROIs = (Vector <Vector <myROI> >) ois.readObject(); // This gives error ois.close(); } catch (Exception e) { IJ.log(e.toString()); } } But this function does not work. First, I get a warning: warning: [unchecked] unchecked cast found : java.lang.Object required: java.util.Vector<java.util.Vector<myROI>> ROIs = (Vector <Vector <myROI> >) ois.readObject(); ^ I Googled for that and see that I can suppress by prepending @SuppressWarnings("unchecked"), but this just makes things worst, as I get an error: <identifier> expected ROIs = (Vector <Vector <myROI> >) ois.readObject(); ^ In any case, if I omit @SuppressWarnings and ignore the warning, the object is not read and an exception is thrown java.io.WriteAbortedException: writing aborted; java.io.NotSerializableException: myROI Again Google tells me myROI needs to implements Serializable. I tried just adding implements Serializable to the class definition, but it is not sufficient. Can anyone give me some hints on how to procede in this case? Also, how to get rid of the typecast warning?

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  • Can i create different observables and different corresponding observers in java?

    - by mithun1538
    Hello everyone, Currently, I have one observable and many observers. What i need is different observables, and depending on the observable, different observers. How do I achieve this? ( For understanding, assume I have different apples - say apple1 apple2... I have observer_1 observing apple1, observer_2 observing apple2, observer_3 observing apple 2 and so on..). I tried creating different objects of the Observable class, but since observers are observing the same class of observable, I don't know how to access a particular instance of the Observable. I have included the following servlet code that contains Observer and Observable classes: public class CustomerServlet extends HttpServlet { public String getNextMessage() { // Create a message sink to wait for a new message from the // message source. return new MessageSink().getNextMessage(source); } @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ObjectOutputStream dout = new ObjectOutputStream(response.getOutputStream()); String recMSG = getNextMessage(); dout.writeObject(recMSG); dout.flush(); } public void broadcastMessage(String message) { // Send the message to all the HTTP-connected clients by giving the // message to the message source source.sendMessage(message); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { try { ObjectInputStream din= new ObjectInputStream(request.getInputStream()); String message = (String)din.readObject(); ObjectOutputStream dout = new ObjectOutputStream(response.getOutputStream()); dout.writeObject("1"); dout.flush(); if (message != null) { broadcastMessage(message); } // Set the status code to indicate there will be no response response.setStatus(response.SC_NO_CONTENT); } catch (Exception e) { e.printStackTrace(); } } @Override public String getServletInfo() { return "Short description"; }// </editor-fold> MessageSource source = new MessageSource(); } class MessageSource extends Observable { public void sendMessage(String message) { setChanged(); notifyObservers(message); } } class MessageSource extends Observable { public void sendMessage(String message) { setChanged(); notifyObservers(message); } } class MessageSink implements Observer { String message = null; // set by update() and read by getNextMessage() // Called by the message source when it gets a new message synchronized public void update(Observable o, Object arg) { // Get the new message message = (String)arg; // Wake up our waiting thread notify(); } // Gets the next message sent out from the message source synchronized public String getNextMessage(MessageSource source) { // Tell source we want to be told about new messages source.addObserver(this); // Wait until our update() method receives a message while (message == null) { try { wait(); } catch (Exception e) { System.out.println("Exception has occured! ERR ERR ERR"); } } // Tell source to stop telling us about new messages source.deleteObserver(this); // Now return the message we received // But first set the message instance variable to null // so update() and getNextMessage() can be called again. String messageCopy = message; message = null; return messageCopy; } }

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  • Java File URI error ?

    - by Frank
    I need to get a file object online, and I know the file is located at : http://nmjava.com/Dir_App_IDs/Dir_GlassPaneDemo/GlassPaneDemo_2010_04_06_15_00_SNGRGLJAMX If I paste it into my browser's url, I'll be able to download this file, now I'm trying to get it with Java, my code looks like this : String File_Url="http://nmjava.com/Dir_App_IDs/Dir_GlassPaneDemo/GlassPaneDemo_2010_04_06_15_00_SNGRGLJAMX"; Object myObject=Get_Online_File(new URI(File_Url)); Object Get_Online_File(URI File_Uri) throws IOException { return readObject(new ObjectInputStream(new FileInputStream(new File(File_Uri)))); } public static synchronized Object readObject(ObjectInput in) throws IOException { Object o; ...... return o; } But I got the following error message : java.lang.IllegalArgumentException: URI scheme is not "file" at java.io.File.<init>(File.java:366) Why ? How to fix it ? Frank

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  • Java programming accessing object variables

    - by Haxed
    Helo, there are 3 files, CustomerClient.java, CustomerServer.java and Customer.java PROBLEM: In the CustomerServer.java file, i get an error when I compile the CustomerServer.java at line : System.out.println(a[k].getName()); ERROR: init: deps-jar: Compiling 1 source file to C:\Documents and Settings\TLNA\My Documents\NetBeansProjects\Server\build\classes C:\Documents and Settings\TLNA\My Documents\NetBeansProjects\Server\src\CustomerServer.java:44: cannot find symbol symbol : method getName() location: class Customer System.out.println(a[k].getName()); 1 error BUILD FAILED (total time: 0 seconds) CustomerClient.java import java.io.*; import java.net.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.border.*; public class CustomerClient extends JApplet { private JTextField jtfName = new JTextField(32); private JTextField jtfSeatNo = new JTextField(32); // Button for sending a student to the server private JButton jbtRegister = new JButton("Register to the Server"); // Indicate if it runs as application private boolean isStandAlone = false; // Host name or ip String host = "localhost"; public void init() { JPanel p1 = new JPanel(); p1.setLayout(new GridLayout(2, 1)); p1.add(new JLabel("Name")); p1.add(jtfName); p1.add(new JLabel("Seat No.")); p1.add(jtfSeatNo); add(p1, BorderLayout.CENTER); add(jbtRegister, BorderLayout.SOUTH); // Register listener jbtRegister.addActionListener(new ButtonListener()); // Find the IP address of the Web server if (!isStandAlone) { host = getCodeBase().getHost(); } } /** Handle button action */ private class ButtonListener implements ActionListener { public void actionPerformed(ActionEvent e) { try { // Establish connection with the server Socket socket = new Socket(host, 8000); // Create an output stream to the server ObjectOutputStream toServer = new ObjectOutputStream(socket.getOutputStream()); // Get text field String name = jtfName.getText().trim(); String seatNo = jtfSeatNo.getText().trim(); // Create a Student object and send to the server Customer s = new Customer(name, seatNo); toServer.writeObject(s); } catch (IOException ex) { System.err.println(ex); } } } /** Run the applet as an application */ public static void main(String[] args) { // Create a frame JFrame frame = new JFrame("Register Student Client"); // Create an instance of the applet CustomerClient applet = new CustomerClient(); applet.isStandAlone = true; // Get host if (args.length == 1) { applet.host = args[0]; // Add the applet instance to the frame } frame.add(applet, BorderLayout.CENTER); // Invoke init() and start() applet.init(); applet.start(); // Display the frame frame.pack(); frame.setVisible(true); } } CustomerServer.java import java.io.*; import java.net.*; public class CustomerServer { private String name; private int i; private ObjectOutputStream outputToFile; private ObjectInputStream inputFromClient; public static void main(String[] args) { new CustomerServer(); } public CustomerServer() { Customer[] a = new Customer[30]; try { // Create a server socket ServerSocket serverSocket = new ServerSocket(8000); System.out.println("Server started "); // Create an object ouput stream outputToFile = new ObjectOutputStream( new FileOutputStream("student.dat", true)); while (true) { // Listen for a new connection request Socket socket = serverSocket.accept(); // Create an input stream from the socket inputFromClient = new ObjectInputStream(socket.getInputStream()); // Read from input //Object object = inputFromClient.readObject(); for (int k = 0; k <= 2; k++) { if (a[k] == null) { a[k] = (Customer) inputFromClient.readObject(); // Write to the file outputToFile.writeObject(a[k]); //System.out.println("A new student object is stored"); System.out.println(a[k].getName()); break; } if (k == 2) { //fully booked outputToFile.writeObject("All seats are booked"); break; } } } } catch (ClassNotFoundException ex) { ex.printStackTrace(); } catch (IOException ex) { ex.printStackTrace(); } finally { try { inputFromClient.close(); outputToFile.close(); } catch (Exception ex) { ex.printStackTrace(); } } } } Customer.java public class Customer implements java.io.Serializable { private String name; private String seatno; public Customer(String name, String seatno) { this.name = name; this.seatno = seatno; } public String getName() { return name; } public String getSeatNo() { return seatno; } }

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  • Custom ArrayList serialization

    - by rayman
    Hi, i was trying to serialize an ArrayList which contacins custom objects. I`am serializing it in a servlet(server side), and deserialize at the client side. (using ObjectOutputStream,ObjectInputStream) it worked fine, when I work with ArrayList< String but when i tried it with ArrayList< MyObject i couldnt get any results in the client side, this is the exception: java.lang.ClassNotFoundException: web.MyObject *ofcourse that i have done this: MyObject implements Serializable ... MyObject contains only String fields in it. what have I done worng? Thanks, ray.

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  • Java, server client TCP communication ends with RST

    - by Senne
    I'm trying to figure out if this is normal. Because without errors, a connection should be terminated by: FIN -> <- ACK <- FIN ACK -> I get this at the end of a TCP connection (over SSL, but i also get it with non-encrypted): From To 1494 server client TCP search-agent > 59185 [PSH, ACK] Seq=25974 Ack=49460 Win=63784 Len=50 1495 client server TCP 59185 > search-agent [ACK] Seq=49460 Ack=26024 Win=63565 Len=0 1496 client server TCP 59185 > search-agent [PSH, ACK] Seq=49460 Ack=26024 Win=63565 Len=23 1497 client server TCP 59185 > search-agent [FIN, ACK] Seq=49483 Ack=26024 Win=63565 Len=0 1498 server client TCP search-agent > 59185 [PSH, ACK] Seq=26024 Ack=49484 Win=63784 Len=23 1499 client server TCP 59185 > search-agent [RST, ACK] Seq=49484 Ack=26047 Win=0 Len=0 The client exits normally and reaches socket.close, shouldn't then the connection be shut down normally, without a reset? I can't find anything about the TCP streams of java on google... Here is my code: Server: package Security; import java.io.*; import java.net.*; import javax.net.ServerSocketFactory; import javax.net.ssl.*; import java.util.*; public class SSLDemoServer { private static ServerSocket serverSocket; private static final int PORT = 1234; public static void main(String[] args) throws IOException { int received = 0; String returned; ObjectInputStream input = null; PrintWriter output = null; Socket client; System.setProperty("javax.net.ssl.keyStore", "key.keystore"); System.setProperty("javax.net.ssl.keyStorePassword", "vwpolo"); System.setProperty("javax.net.ssl.trustStore", "key.keystore"); System.setProperty("javax.net.ssl.trustStorePassword", "vwpolo"); try { System.out.println("Trying to set up server ..."); ServerSocketFactory factory = SSLServerSocketFactory.getDefault(); serverSocket = factory.createServerSocket(PORT); System.out.println("Server started!\n"); } catch (IOException ioEx) { System.out.println("Unable to set up port!"); ioEx.printStackTrace(); System.exit(1); } while(true) { client = serverSocket.accept(); System.out.println("Client trying to connect..."); try { System.out.println("Trying to create inputstream..."); input = new ObjectInputStream(client.getInputStream()); System.out.println("Trying to create outputstream..."); output = new PrintWriter(client.getOutputStream(), true); System.out.println("Client successfully connected!"); while( true ) { received = input.readInt(); returned = Integer.toHexString(received); System.out.print(" " + received); output.println(returned.toUpperCase()); } } catch(SSLException sslEx) { System.out.println("Connection failed! (non-SSL connection?)\n"); client.close(); continue; } catch(EOFException eofEx) { System.out.println("\nEnd of client data.\n"); } catch(IOException ioEx) { System.out.println("I/O problem! (correct inputstream?)"); } try { input.close(); output.close(); } catch (Exception e) { } client.close(); System.out.println("Client closed.\n"); } } } Client: package Security; import java.io.*; import java.net.*; import javax.net.ssl.*; import java.util.*; public class SSLDemoClient { private static InetAddress host; private static final int PORT = 1234; public static void main(String[] args) { System.setProperty("javax.net.ssl.keyStore", "key.keystore"); System.setProperty("javax.net.ssl.keyStorePassword", "vwpolo"); System.setProperty("javax.net.ssl.trustStore", "key.keystore"); System.setProperty("javax.net.ssl.trustStorePassword", "vwpolo"); System.out.println("\nCreating SSL socket ..."); SSLSocket socket = null; try { host = InetAddress.getByName("192.168.56.101"); SSLSocketFactory factory = (SSLSocketFactory) SSLSocketFactory.getDefault(); socket = (SSLSocket) factory.createSocket(host, PORT); socket.startHandshake(); } catch(UnknownHostException uhEx) { System.out.println("\nHost ID not found!\n"); System.exit(1); } catch(SSLException sslEx) { System.out.println("\nHandshaking unsuccessful ..."); System.exit(1); } catch (IOException e) { e.printStackTrace(); } System.out.println("\nHandshaking succeeded ...\n"); SSLClientThread client = new SSLClientThread(socket); SSLReceiverThread receiver = new SSLReceiverThread(socket); client.start(); receiver.start(); try { client.join(); receiver.join(); System.out.println("Trying to close..."); socket.close(); } catch(InterruptedException iEx) { iEx.printStackTrace(); } catch(IOException ioEx) { ioEx.printStackTrace(); } System.out.println("\nClient finished."); } } class SSLClientThread extends Thread { private SSLSocket socket; public SSLClientThread(SSLSocket s) { socket = s; } public void run() { try { ObjectOutputStream output = new ObjectOutputStream(socket.getOutputStream()); for( int i = 1; i < 1025; i++) { output.writeInt(i); sleep(10); output.flush(); } output.flush(); sleep(1000); output.close(); } catch(IOException ioEx) { System.out.println("Socket closed or unable to open socket."); } catch(InterruptedException iEx) { iEx.printStackTrace(); } } } class SSLReceiverThread extends Thread { private SSLSocket socket; public SSLReceiverThread(SSLSocket s) { socket = s; } public void run() { String response = null; BufferedReader input = null; try { input = new BufferedReader( new InputStreamReader(socket.getInputStream())); try { response = input.readLine(); while(!response.equals(null)) { System.out.print(response + " "); response = input.readLine(); } } catch(Exception e) { System.out.println("\nEnd of server data.\n"); } input.close(); } catch(IOException ioEx) { ioEx.printStackTrace(); } } }

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  • Help with chat server

    - by mithun1538
    I am designing a chat server in java. The communication is Http based and not socket based. In the client side I have an applet. In the server side I have a servlet. Applet: I create a new thread to listen for incoming messages(GET method). The main thread is used to send messages(POST messages). The partial code is : public void start() { System.out.println("Creating new thread"); Thread thread = new Thread(this); thread.start(); } private String getNewMessage() { System.out.println("Inside getNewMessage"); String msg = null; try { while(msg == null) { System.out.println("Trying to listen to servlet"); URL servlet = new URL(getCodeBase(), "NewServlet?mode=msg"); URLConnection con = servlet.openConnection(); con.setUseCaches(false); DataInputStream din = new DataInputStream(new BufferedInputStream(con.getInputStream())); msg = din.readUTF(); System.out.println("message read :" + msg); } } catch (Exception e) { e.printStackTrace(); } return msg + "\n"; } public void run() { System.out.println("Inside new thread"); while(true) { System.out.println("inside first while"); String newMsg = getNewMessage(); chatOutput.append(newMsg); System.out.println("Appended!!"); } } private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { String message = chatInput.getText(); chatInput.setText(""); chatOutput.append(message + "\n"); try { System.out.println("Trying to send msg :" + message); URL url = new URL(getCodeBase(), "NewServlet"); URLConnection servletConnection = url.openConnection(); servletConnection.setDoInput(true); servletConnection.setDoOutput(true); servletConnection.setUseCaches(false); servletConnection.setRequestProperty("Content-Type", "application/octet-stream"); ObjectOutputStream out = new ObjectOutputStream(servletConnection.getOutputStream()); out.writeObject(message); out.flush(); out.close(); System.out.println("Message sent!"); } catch (Exception e) { e.printStackTrace(); } } This next code is from the servlet side. it uses the Observable interface to identify and send messages to clients. public class NewServlet extends HttpServlet { // getNextMessage() returns the next new message. // It blocks until there is one. public String getNextMessage() { // Create a message sink to wait for a new message from the // message source. System.out.println("inside getNextMessage"); return new MessageSink().getNextMessage(source);} @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("Inside Doget"); response.setContentType("text/plain"); PrintWriter out = response.getWriter(); out.println(getNextMessage()); } // broadcastMessage() informs all currently listening clients that there // is a new message. Causes all calls to getNextMessage() to unblock. public void broadcastMessage(String message) { // Send the message to all the HTTP-connected clients by giving the // message to the message source source.sendMessage(message); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("Inside DoPost"); try { ObjectInputStream din= new ObjectInputStream(request.getInputStream()); String message = (String)din.readObject(); System.out.println("received msg"); if (message != null) broadcastMessage(message); System.out.println("Called broadcast"); // Set the status code to indicate there will be no response response.setStatus(response.SC_NO_CONTENT); } catch (Exception e) { e.printStackTrace(); } } /** * Returns a short description of the servlet. * @return a String containing servlet description */ @Override public String getServletInfo() { return "Short description"; } MessageSource source = new MessageSource();} class MessageSource extends Observable { public void sendMessage(String message) { System.out.println("inside sendMsg"); setChanged(); notifyObservers(message); } } class MessageSink implements Observer { String message = null; // set by update() and read by getNextMessage() // Called by the message source when it gets a new message synchronized public void update(Observable o, Object arg) { // Get the new message message = (String)arg; // Wake up our waiting thread notify(); } // Gets the next message sent out from the message source synchronized public String getNextMessage(MessageSource source) { // Tell source we want to be told about new messages source.addObserver(this); System.out.println("AddedObserver"); // Wait until our update() method receives a message while (message == null) { try { wait(); } catch (Exception ignored) { } } // Tell source to stop telling us about new messages source.deleteObserver(this); // Now return the message we received // But first set the message instance variable to null // so update() and getNextMessage() can be called again. String messageCopy = message; message = null; System.out.println("Returning msg"); return messageCopy; } } As you can see I have included System.out.println("Some message"); in some places. this was just for debugging purposes. In java console, i get the following output: Creating new thread Inside new thread. inside first while. Inside getNewMessage. Trying to listen to servlet. In the servlet side, i get the following output in the tomcat logs: Inside Doget. inside getNextMessage. AddedObserver. After i type a message in the applet, and send it, I get the foll output in java console: Trying to send msg :you deR?? Message sent! But in servlet side, I dont get anything in the logs. I used the O'Reily Java Servlet Programming as reference(The observer interface comes from there). But I am not getting any chat communication between two clients. As can be understood from the logs, the POST method is not called. Any reason for this?

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  • Retrieve data from .dat file.

    - by Zach
    We have an application which requires us to read data from a file (.dat) dynamically using deserialization. We are actually getting first object and it throws null pointer exception when we are accessing other objects using a "for" loop. File file=null; FileOutputStream fos=null; BufferedOutputStream bos=null; ObjectOutputStream oos=null; try{ file=new File("account4.dat"); fos=new FileOutputStream(file,true); bos=new BufferedOutputStream(fos); oos=new ObjectOutputStream(bos); oos.writeObject(m); System.out.println("object serialized"); amlist=new MemberAccountList(); oos.close(); } catch(Exception ex){ ex.printStackTrace(); } Reading objects: try{ MemberAccount m1; file=new File("account4.dat");//add your code here fis=new FileInputStream(file); bis=new BufferedInputStream(fis); ois=new ObjectInputStream(bis); System.out.println(ois.readObject()); while(ois.readObject()!=null){ m1=(MemberAccount)ois.readObject(); System.out.println(m1.toString()); }/mList.addElement(m1); // Here we have the issue throwing null pointer exception Enumeration elist=mList.elements(); while(elist.hasMoreElements()){ obj=elist.nextElement(); System.out.println(obj.toString()); }/ } catch(ClassNotFoundException e){ } catch(EOFException e){ System.out.println("end"); } catch(Exception ex){ ex.printStackTrace(); }

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  • How to identify the type of socket data?

    - by Nitesh Panchal
    Hello, May be i am not able to express my doubt properly in this question but still i will try. Basically i created a simple socket based chat program and everything works fine. But i think i have made many patches in it from the design point of view. I have used ObjectInputStream and ObjectOutputStreams in my program. The question i want to ask is how do i identify the different type of data that i send across the network? say if it is simple String type object i directly add to List<String> chatMessages. Now if want to ban certain users i created an another class :- public class User{ private String name; private String id; //getters and setters } This User class means no importance to me till now but i only created it to properly identify the action. Thus if i receive an instanceOf User i can be sure that some user is to be banned. That way i dont have to hardcode strings. I mean first i thought of sending something like "Banned User :" + userName and then i used to check if string startsWith "Banned User :" then i take some action :p. I've created a User class but it means no importance to me in my program. I want to know whether directly sending strings is good way or create a class for every action that is good. If i am not clear please let me know. If i have hundreds of action do i have to create hundreds of classes so i can check via instanceOf? Say now if i plan to create a BUZZ like facility that is available in yahoo messenger. Should i again create an another class named BUZZ? so it can be identified easily?

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  • How to read data from file(.dat) in append mode

    - by govardhan
    We have an application which requires us to read data from a file (.dat) dynamically using deserialization. We are actually getting first object and it throws null pointer exception and "java.io.StreamCorruptedException:invalid type code:AC" when we are accessing other objects using a "for" loop. File file=null; FileOutputStream fos=null; BufferedOutputStream bos=null; ObjectOutputStream oos=null; try{ file=new File("account4.dat"); fos=new FileOutputStream(file,true); bos=new BufferedOutputStream(fos); oos=new ObjectOutputStream(bos); oos.writeObject(m); System.out.println("object serialized"); amlist=new MemberAccountList(); oos.close(); } catch(Exception ex){ ex.printStackTrace(); } Reading objects: try{ MemberAccount m1; file=new File("account4.dat");//add your code here fis=new FileInputStream(file); bis=new BufferedInputStream(fis); ois=new ObjectInputStream(bis); System.out.println(ois.readObject()); **while(ois.readObject()!=null){ m1=(MemberAccount)ois.readObject(); System.out.println(m1.toString()); }/*mList.addElement(m1);** // Here we have the issue throwing null pointer exception Enumeration elist=mList.elements(); while(elist.hasMoreElements()){ obj=elist.nextElement(); System.out.println(obj.toString()); }*/ } catch(ClassNotFoundException e){ } catch(EOFException e){ System.out.println("end"); } catch(Exception ex){ ex.printStackTrace(); }

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  • final transient fields and serialization

    - by doublep
    Is it possible to have final transient fields that are set to any non-default value after serialization in Java? My usecase is a cache variable — that's why it is transient. I also have a habit of making Map fields that won't be changed (i.e. contents of the map is changed, but object itself remains the same) final. However, these attributes seem to be contradictory — while compiler allows such a combination, I cannot have the field set to anything but null after unserialization. I tried the following, without success: simple field initialization (shown in the example): this is what I normally do, but the initialization doesn't seem to happen after unserialization; initialization in constructor (I believe this is semantically the same as above though); assigning the field in readObject() — cannot be done since the field is final. In the example cache is public only for testing. import java.io.*; import java.util.*; public class test { public static void main (String[] args) throws Exception { X x = new X (); System.out.println (x + " " + x.cache); ByteArrayOutputStream buffer = new ByteArrayOutputStream (); new ObjectOutputStream (buffer).writeObject (x); x = (X) new ObjectInputStream (new ByteArrayInputStream (buffer.toByteArray ())).readObject (); System.out.println (x + " " + x.cache); } public static class X implements Serializable { public final transient Map <Object, Object> cache = new HashMap <Object, Object> (); } } Output: test$X@1a46e30 {} test$X@190d11 null

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  • C struct written in file, open with Java

    - by DaunnC
    For example in C I have structure: typedef struct { int number; double x1; double y1; double x2; double y2; double x3; double y3; } CTRstruct;` Then I write it to file fwrite(&tr, 1, sizeof(tr), fp); (tr - its CTRstruct var, fp - File pointer); Then I need to read it with Java! I really don't know how to read struct from file... I tried to read it with ObjectInputStream(), last idea is to read with RandomAccessFile() but I also don't know how to... (readLong(), readDouble() also doesn't work, it works ofcource but doesn't read correct data). So, any idea how to read C struct from binary file with Java? If it's interesting, my version to read integer (but it's ugly, & I don't know what to do with double): public class MyDataInputStream extends DataInputStream{ public MyDataInputStream(InputStream AIs) { super(AIs); } public int readInt1() throws IOException{ int ch1 = in.read(); int ch2 = in.read(); int ch3 = in.read(); int ch4 = in.read(); if ((ch1 | ch2 | ch3 | ch4) < 0) throw new EOFException(); return ((ch4 << 24) + (ch3 << 16) + (ch2 << 8) + (ch1 << 0)); } with double we can deal the same way (like with int or with long (8bytes) & then convert to double with native func).

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  • passing reference of class to another class android error

    - by prolink007
    I recently asked the precursor to this question and had a great reply. However, when i was working this into my android application i am getting an unexpected error and was wondering if everyone could take a look at my code and help me see what i am doing wrong. Link to the initial question: passing reference of class to another class My ERROR: "The constructor ConnectDevice(new View.OnClickListener(){}) is undefined" The above is an error detected by eclipse. Thanks in advance! Below are My code snippets: public class SmartApp extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.intro); final Button connectDeviceButton = (Button) findViewById(R.id.connectDeviceButton); connectDeviceButton.setOnClickListener( new View.OnClickListener() { @Override public void onClick(View v) { Thread cThread = new Thread(new ConnectDevice(this)); cThread.start(); } }); } } public class ConnectDevice implements Runnable { private boolean connected; private SmartApp smartAppRef; private ObjectInputStream ois; public ConnectDevice(SmartApp smartAppRef) { this.smartAppRef = smartAppRef; } }

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  • What is wrong with this Asynchronus task?

    - by bluebrain
    the method onPostExecute simply was not executed, I have seen 16 at LogCat but I can not see 16 in LogCAT. I tried to debug it, it seemed that it goes to the first line of the class (package line) after return statement. private class Client extends AsyncTask<Integer, Void, Integer> { protected Integer doInBackground(Integer... params) { Log.e(TAG,10+""); try { socket = new Socket(target, port); Log.e(TAG,11+""); oos = new ObjectOutputStream(socket.getOutputStream()); Log.e(TAG,14+""); ois = new ObjectInputStream(socket.getInputStream()); Log.e(TAG,15+""); } catch (UnknownHostException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } Log.e(TAG,16+""); return 1; } protected void onPostExecute(Integer result) { Log.e(TAG,13+""); try { Log.e(TAG,12+""); oos.writeUTF(key); Log.e(TAG,13+""); if (ois.readInt() == OKAY) { isConnected = true; Log.e(TAG,14+""); }else{ Log.e(TAG,15+""); isConnected = false; } } catch (IOException e) { e.printStackTrace(); isClosed = true; } } }

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  • Optimizing a thread safe Java NIO / Serialization / FIFO Queue [migrated]

    - by trialcodr
    I've written a thread safe, persistent FIFO for Serializable items. The reason for reinventing the wheel is that we simply can't afford any third party dependencies in this project and want to keep this really simple. The problem is it isn't fast enough. Most of it is undoubtedly due to reading and writing directly to disk but I think we should be able to squeeze a bit more out of it anyway. Any ideas on how to improve the performance of the 'take'- and 'add'-methods? /** * <code>DiskQueue</code> Persistent, thread safe FIFO queue for * <code>Serializable</code> items. */ public class DiskQueue<ItemT extends Serializable> { public static final int EMPTY_OFFS = -1; public static final int LONG_SIZE = 8; public static final int HEADER_SIZE = LONG_SIZE * 2; private InputStream inputStream; private OutputStream outputStream; private RandomAccessFile file; private FileChannel channel; private long offs = EMPTY_OFFS; private long size = 0; public DiskQueue(String filename) { try { boolean fileExists = new File(filename).exists(); file = new RandomAccessFile(filename, "rwd"); if (fileExists) { size = file.readLong(); offs = file.readLong(); } else { file.writeLong(size); file.writeLong(offs); } } catch (FileNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } channel = file.getChannel(); inputStream = Channels.newInputStream(channel); outputStream = Channels.newOutputStream(channel); } /** * Add item to end of queue. */ public void add(ItemT item) { try { synchronized (this) { channel.position(channel.size()); ObjectOutputStream s = new ObjectOutputStream(outputStream); s.writeObject(item); s.flush(); size++; file.seek(0); file.writeLong(size); if (offs == EMPTY_OFFS) { offs = HEADER_SIZE; file.writeLong(offs); } notify(); } } catch (IOException e) { throw new RuntimeException(e); } } /** * Clears overhead by moving the remaining items up and shortening the file. */ public synchronized void defrag() { if (offs > HEADER_SIZE && size > 0) { try { long totalBytes = channel.size() - offs; ByteBuffer buffer = ByteBuffer.allocateDirect((int) totalBytes); channel.position(offs); for (int bytes = 0; bytes < totalBytes;) { int res = channel.read(buffer); if (res == -1) { throw new IOException("Failed to read data into buffer"); } bytes += res; } channel.position(HEADER_SIZE); buffer.flip(); for (int bytes = 0; bytes < totalBytes;) { int res = channel.write(buffer); if (res == -1) { throw new IOException("Failed to write buffer to file"); } bytes += res; } offs = HEADER_SIZE; file.seek(LONG_SIZE); file.writeLong(offs); file.setLength(HEADER_SIZE + totalBytes); } catch (IOException e) { throw new RuntimeException(e); } } } /** * Returns the queue overhead in bytes. */ public synchronized long overhead() { return (offs == EMPTY_OFFS) ? 0 : offs - HEADER_SIZE; } /** * Returns the first item in the queue, blocks if queue is empty. */ public ItemT peek() throws InterruptedException { block(); synchronized (this) { if (offs != EMPTY_OFFS) { return readItem(); } } return peek(); } /** * Returns the number of remaining items in queue. */ public synchronized long size() { return size; } /** * Removes and returns the first item in the queue, blocks if queue is empty. */ public ItemT take() throws InterruptedException { block(); try { synchronized (this) { if (offs != EMPTY_OFFS) { ItemT result = readItem(); size--; offs = channel.position(); file.seek(0); if (offs == channel.size()) { truncate(); } file.writeLong(size); file.writeLong(offs); return result; } } return take(); } catch (IOException e) { throw new RuntimeException(e); } } /** * Throw away all items and reset the file. */ public synchronized void truncate() { try { offs = EMPTY_OFFS; file.setLength(HEADER_SIZE); size = 0; } catch (IOException e) { throw new RuntimeException(e); } } /** * Block until an item is available. */ protected void block() throws InterruptedException { while (offs == EMPTY_OFFS) { try { synchronized (this) { wait(); file.seek(LONG_SIZE); offs = file.readLong(); } } catch (IOException e) { throw new RuntimeException(e); } } } /** * Read and return item. */ @SuppressWarnings("unchecked") protected ItemT readItem() { try { channel.position(offs); return (ItemT) new ObjectInputStream(inputStream).readObject(); } catch (ClassNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } } }

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  • Why can't Java servlet sent out an object ?

    - by Frank
    I use the following method to send out an object from a servlet : public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException { String Full_URL=request.getRequestURL().append("?"+request.getQueryString()).toString(); String Contact_Id=request.getParameter("Contact_Id"); String Time_Stamp=Get_Date_Format(6),query="select from "+Contact_Info_Entry.class.getName()+" where Contact_Id == '"+Contact_Id+"' order by Contact_Id desc"; PersistenceManager pm=null; try { pm=PMF.get().getPersistenceManager(); // note that this returns a list, there could be multiple, DataStore does not ensure uniqueness for non-primary key fields List<Contact_Info_Entry> results=(List<Contact_Info_Entry>)pm.newQuery(query).execute(); Write_Serialized_XML(response.getOutputStream(),results.get(0)); } catch (Exception e) { Send_Email(Email_From,Email_To,"Check_License_Servlet Error [ "+Time_Stamp+" ]",new Text(e.toString()+"\n"+Get_Stack_Trace(e)),null); } finally { pm.close(); } } /** Writes the object and CLOSES the stream. Uses the persistance delegate registered in this class. * @param os The stream to write to. * @param o The object to be serialized. */ public static void writeXMLObject(OutputStream os,Object o) { // Classloader reference must be set since netBeans uses another class loader to loead the bean wich will fail in some circumstances. ClassLoader oldClassLoader=Thread.currentThread().getContextClassLoader(); Thread.currentThread().setContextClassLoader(Check_License_Servlet.class.getClassLoader()); XMLEncoder encoder=new XMLEncoder(os); encoder.setExceptionListener(new ExceptionListener() { public void exceptionThrown(Exception e) { e.printStackTrace(); }}); encoder.writeObject(o); encoder.flush(); encoder.close(); Thread.currentThread().setContextClassLoader(oldClassLoader); } private static ByteArrayOutputStream writeOutputStream=new ByteArrayOutputStream(16384); /** Writes an object to XML. * @param out The boject out to write to. [ Will not be closed. ] * @param o The object to write. */ public static synchronized void writeAsXML(ObjectOutput out,Object o) throws IOException { writeOutputStream.reset(); writeXMLObject(writeOutputStream,o); byte[] Bt_1=writeOutputStream.toByteArray(); byte[] Bt_2=new Des_Encrypter().encrypt(Bt_1,Key); out.writeInt(Bt_2.length); out.write(Bt_2); out.flush(); out.close(); } public static synchronized void Write_Serialized_XML(OutputStream Output_Stream,Object o) throws IOException { writeAsXML(new ObjectOutputStream(Output_Stream),o); } At the receiving end the code look like this : File_Url="http://"+Site_Url+App_Dir+File_Name; try { Contact_Info_Entry Online_Contact_Entry=(Contact_Info_Entry)Read_Serialized_XML(new URL(File_Url)); } catch (Exception e) { e.printStackTrace(); } private static byte[] readBuf=new byte[16384]; public static synchronized Object readAsXML(ObjectInput in) throws IOException { // Classloader reference must be set since netBeans uses another class loader to load the bean which will fail under some circumstances. ClassLoader oldClassLoader=Thread.currentThread().getContextClassLoader(); Thread.currentThread().setContextClassLoader(Tool_Lib_Simple.class.getClassLoader()); int length=in.readInt(); readBuf=new byte[length]; in.readFully(readBuf,0,length); byte Bt[]=new Des_Encrypter().decrypt(readBuf,Key); XMLDecoder dec=new XMLDecoder(new ByteArrayInputStream(Bt,0,Bt.length)); Object o=dec.readObject(); Thread.currentThread().setContextClassLoader(oldClassLoader); in.close(); return o; } public static synchronized Object Read_Serialized_XML(URL File_Url) throws IOException { return readAsXML(new ObjectInputStream(File_Url.openStream())); } But I can't get the object from the Java app that's on the receiving end, why ? The error messages look like this : java.lang.ClassNotFoundException: PayPal_Monitor.Contact_Info_Entry Continuing ... java.lang.NullPointerException: target should not be null Continuing ... java.lang.NullPointerException: target should not be null Continuing ... java.lang.NullPointerException: target should not be null Continuing ...

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  • Java deadlock problem....

    - by markovuksanovic
    I am using java sockets for communication. On the client side I have some processing and at this point I send an object to the cient. The code is as follows: while (true) { try { Socket server = new Socket("localhost", 3000); OutputStream os = server.getOutputStream(); InputStream is = server.getInputStream(); CommMessage commMessage = new CommMessageImpl(); ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(bos); oos.writeObject(commMessage); os.write(bos.toByteArray()); os.flush(); byte[] buff = new byte[512]; int bytesRead = 0; ByteArrayOutputStream receivedObject = new ByteArrayOutputStream(); while ((bytesRead = is.read(buff)) > -1) { receivedObject.write(buff, 0, bytesRead); System.out.println(receivedObject); } os.close(); Thread.sleep(10000); } catch (IOException e) { } catch (InterruptedException e) { } } Next on the server side I have the following code to read the object and write the response (Which is just an echo message) public void startServer() { Socket client = null; try { server = new ServerSocket(3000); logger.log(Level.INFO, "Waiting for connections."); client = server.accept(); logger.log(Level.INFO, "Accepted a connection from: " + client.getInetAddress()); os = new ObjectOutputStream(client.getOutputStream()); is = new ObjectInputStream(client.getInputStream()); // Read contents of the stream and store it into a byte array. byte[] buff = new byte[512]; int bytesRead = 0; ByteArrayOutputStream receivedObject = new ByteArrayOutputStream(); while ((bytesRead = is.read(buff)) > -1) { receivedObject.write(buff, 0, bytesRead); } // Check if received stream is CommMessage or not contents. CommMessage commMessage = getCommMessage(receivedObject); if (commMessage != null) { commMessage.setSessionState(this.sessionManager.getState().getState()); ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(bos); oos.writeObject(commMessage); os.write(bos.toByteArray()); System.out.println(commMessage.getCommMessageType()); } else { processData(receivedObject, this.sessionManager); } os.flush(); } catch (IOException e) { } finally { try { is.close(); os.close(); client.close(); server.close(); } catch (IOException e) { } } } The above code works ok if I do not try to read data on the client side (If i exclude the code related to reading). But if I have that code, for some reason, I get some kind of deadlock when accessing input streams. Any ideas what I might have done wrong? Thanks in advance.

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  • Adding a JPanel to another JPanel having TableLayout

    - by user253530
    I am trying to develop a map editor in java. My map window receives as a constructor a Map object. From that map object i am able to retrieve the Grid and every item in the grid along with other getters and setters. The problem is that even though the Mapping extends JComponent, when I place it in a panel it is not painted. I have overridden the paint method to satisfy my needs. Here is the code, maybe you could help me. public class MapTest extends JFrame implements ActionListener { private JPanel mainPanel; private JPanel mapPanel; private JPanel minimapPanel; private JPanel relationPanel; private TableLayout tableLayout; private JPanel tile; MapTest(Map map) { mainPanel = (JPanel) getContentPane(); mapPanel = new JPanel(); populateMapPanel(map); mainPanel.add(mapPanel); this.setPreferredSize(new Dimension(800, 600)); this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); this.setVisible(true); } private double[][] generateTableLayoutSize(int x, int y, int size) { double panelSize[][] = new double[x][y]; for (int i = 0; i < x; i++) { for (int j = 0; j < y; j++) { panelSize[i][j] = size; } } return panelSize; } private void populateMapPanel(Map map) { double[][] layoutSize = generateTableLayoutSize(map.getMapGrid().getRows(), map.getMapGrid().getColumns(), 50); tableLayout = new TableLayout(layoutSize); for(int i = 0; i < map.getMapGrid().getRows(); i++) { for(int j = 0; j < map.getMapGrid().getColumns(); j++) { tile = new JPanel(); tile.setName(String.valueOf(((Mapping)map.getMapGrid().getItem(i, j)).getCharacter())); tile.add(map.getMapItem(i, j)); String constraint = i + "," + j; mapPanel.add(tile, constraint); } } mapPanel.validate(); mapPanel.repaint(); } public void actionPerformed(ActionEvent e) { throw new UnsupportedOperationException("Not supported yet."); } } My Mapping Class public class Mapping extends JComponent implements Serializable{ private BufferedImage image; private Character character; //default public Mapping() { super(); this.image = null; this.character = '\u0000'; } //Mapping from image and char public Mapping(BufferedImage image, char character) { super(); this.image = image; this.character = character; } //Mapping from file and char public Mapping(File file, char character) { try { this.image = ImageIO.read(file); this.character = character; } catch (IOException ex) { System.out.println(ex); } } public char getCharacter() { return character; } public void setCharacter(char character) { this.character = character; } public BufferedImage getImage() { return image; } public void setImage(BufferedImage image) { this.image = image; repaint(); } @Override /*Two mappings are consider the same if -they have the same image OR -they have the same character OR -both of the above*/ public boolean equals(Object mapping) { if (this == mapping) { return true; } if (mapping instanceof Mapping) { return true; } //WARNING! equals might not work for images return (this.getImage()).equals(((Mapping) mapping).getImage()) || (this.getCharacter()) == (((Mapping) mapping).getCharacter()); } @Override public void paintComponent(Graphics g) { super.paintComponent(g); //g.drawImage(image, 0, 0, null); g.drawImage(image, 0, 0, this.getWidth(), this.getHeight(), null); } // @Override // public Dimension getPreferredSize() { // if (image == null) { // return new Dimension(10, 10); //instead of 100,100 set any prefered dimentions // } else { // return new Dimension(100, 100);//(image.getWidth(null), image.getHeight(null)); // } // } private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException { character = (Character) in.readObject(); image = ImageIO.read(ImageIO.createImageInputStream(in)); } private void writeObject(java.io.ObjectOutputStream out) throws IOException { out.writeObject(character); ImageWriter writer = (ImageWriter) ImageIO.getImageWritersBySuffix("jpg").next(); writer.setOutput(ImageIO.createImageOutputStream(out)); ImageWriteParam param = writer.getDefaultWriteParam(); param.setCompressionMode(ImageWriteParam.MODE_EXPLICIT); param.setCompressionQuality(0.85f); writer.write(null, new IIOImage(image, null, null), param); } }

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