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POImage transmission over HTTP with Java
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copied!<p>Hope the Java experts in stackoverflow can shed some light :</p> <p>We are successfully sending images by serializing the image ( after casting it to Java ImageIcon Serializable type), but the Serialized IO seems expensive ( readObject(), writeObject()), as we keep hitting the "java.lang.OutOfMemoryError: Java heap space" errors in the servlet container.</p> <p>Is there a better way of transmitting image files in Java over HTTP ?</p> <p>The application is using Java Robot class to send desktop images continually to multiple clients over a servlet ( to facilitate the HTTP transmission). Sounds like good advice already, let me post some of the code to give you an idea for my project. I have to use Java ( over the web that is using servlets), and my job depends on this working out ...please help ...</p> <p><em><strong></em>__</strong><em>Adding critical code excerpts from the components <strong></em>__<em>_</em>__<em>_</em>__<em>_</em>__</strong></p> <p>I. ClientApplet (Captures desktop images(sends serialized over sockets to a central ImageBroker)</p> <p>-> II. ImageBroker (Reads Serialized images from ClientApplet over sockets and sends it to servlet to make it available to HTTP viewer applets)</p> <p>-> III. ViewerServlet Forward the images to applets over HTTP</p> <p>-> IV.Applet reading serialized images</p> <pre><code>// I. Client Applet // (sends serialized desktop images to ImageBroker server over TCP sockets ) class ScreenShoot extends Thread { Socket socket = null; Robot robot = null; // Used to capture screen Rectangle rectangle = null; //Used to represent screen dimensions boolean continueLoop = true; //Used to exit the program public ScreenShoot(Socket socket, Robot robot, Rectangle rect) { this.socket = socket; this.robot = robot; rectangle = rect; start(); } public void run() { ObjectOutputStream oos = null; //Used to write an object to the streem try { //Prepare ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream()); } catch (IOException ex) { ex.printStackTrace(); } String Userid = "test"; String ConfId = "ONE"; MyClass sendHeader = new MyClass(Userid,ConfId, 300, 300, 20, 30); System.out.println("sendHeader: " + sendHeader); // Send the header (username, ConferenceID) first before sending the images try { oos.writeObject(sendHeader); System.out.println("sent HEADER object1: "); } catch (IOException ex) { ex.printStackTrace(); } int countRec = 1; while (continueLoop) { //Capture screen BufferedImage image = robot.createScreenCapture(rectangle); /* I have to wrap BufferedImage with ImageIcon because BufferedImage class * does not implement Serializable interface */ ImageIcon imageIcon = new ImageIcon(image); //Send captured screen to the server try { System.out.println("ScreenSpyer:before sending image-writeObject"); // oos.writeObject(imageIcon); oos.writeUnshared(imageIcon); countRec++; if (countRec > 20 ) { oos.reset(); //Clear ObjectOutputStream cache countRec = 1; } System.out.println("ScreenSpyer: New screenshot sent"); } catch (IOException ex) { ex.printStackTrace(); } //wait for 1000ms to redu/ e network traffic try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } </code></pre> <hr> <p>II.Central ImageBroker Server Broker handles images from various senders and traffics them to the right viewers ( coming through a servlet) -Receives images from client screensender applet over TCP sockets - Forwards Serialized images to ViewerServlet</p> <pre><code>// Section READING the incoming images ( this is over simple TCP Sockets) class HandleSenders extends Thread { private Socket socket = null; private WinTest mainprog; private MessageBin source; private InputStream fromServer = null; public HandleSenders(WinTest mainprog, Socket socket, MessageBin source) { super("HandleSenders"); this.socket = socket; this.mainprog = mainprog; this.source = source; } // 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. return new MessageHold().getNextMessage(source); } public void run() { // Reading Images from SnreenSender client ObjectInputStream in = null; byte[] buffer = new byte[256]; int fromServer_val, backup_val =0 ; try { // in = new ObjectInputStream(socket.getInputStream()); fromServer = socket.getInputStream(); in = new ObjectInputStream(fromServer); boolean forever = true; int cntr = 1; boolean contin = true; int counter = 1; boolean Found = false; String theMessage = ""; while (contin) { // if (cntr++ > 5) break; // fromServer_val = fromServer.read(buffer); // dealing with null values which crashes the system, // if for some problem in transmission you get a null, we just put the // previous valid data // into the null one. ImageIcon imageIcon = (ImageIcon)in.readObject(); Found = mainprog.FindViewersAndSend(senderHeader.confid, imageIcon); // Blocks first time and only if the structure has no // clients for this sender if (!Found) theMessage = getNextMessage(); //blocks </code></pre> <p>Section handling SENDING the images to servlets</p> <pre><code> public boolean FindViewersAndSend(String confid, ImageIcon imageIcon) { Iterator it = socketMap.entrySet().iterator(); ObjectOutputStream viewerOut = null; byte[] buffer = new byte[256]; Socket viewerClient = null; OutputStream toClient = null; boolean Found = false; int recordCount = 1; try { while (it.hasNext()) { // Iterating through structures of Viewer servlet socket connections Map.Entry pairs = (Map.Entry)it.next(); socketUserStruct = getSocketDetails((String)pairs.getKey()); if ( socketUserStruct != null && !socketUserStruct.equals ("")) { StructConfId = (String)socketUserStruct.getConfId(); StructUserId = (String)pairs.getKey(); } if (StructConfId.equals(confid)) { Found = true; viewerOut = (ObjectOutputStream)socketUserStruct.getObjectOutputStream(); // write the serialized data to the servlet.... // which in turn sends it to the applet over http // viewerOut.writeObject(imageIcon); viewerOut.writeUnshared(imageIcon); recordCount++; if (recordCount > 10) { viewerOut.flush(); recordCount = 0; } } } } catch (IOException e) { /// clean up removeSocketClient(StructUserId); } return Found; </code></pre> <p>}</p> <hr> <p>III. ViewerServlet - Getting images from Image broker and sends the Serialized image to Applets ( over http)</p> <pre><code>public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, Socket echoSocket = null; PrintWriter out = null; InputStream fromServer = null; byte[] buffer = new byte[256]; int fromServer_val, backup_val = 0; // OutputStream toClient = res.getOutputStream(); try { echoSocket = new Socket("localhost", RES_PORT); out = new PrintWriter(echoSocket.getOutputStream(), true); String screensize = "300"; String viewerHeader = userid+","+confid+","+screensize; out.println(viewerHeader); out.println("bye"); out.flush(); InputStream is = echoSocket.getInputStream(); ObjectInputStream in = new ObjectInputStream(is); ObjectOutputStream oos = new ObjectOutputStream(res.getOutputStream()); try { int recordCount = 1; while (true) { ImageIcon imageIcon = (ImageIcon)in.readObject(); oos.writeObject(imageIcon); if (recordCount++ > 5) { recordCount = 1; oos.flush(); } // oos.flush(); } } catch (ClassNotFoundException e) { ....... } catch (IOException ex) { ex.printStackTrace(); } } catch (IOException e) { // show("plainViewAdapter-doGet:4"); fromServer.close(); } } </code></pre> <hr> <p>IV. Viewer Applet ( Connecting to the Viewer Servlet to receive the images )</p> <pre><code>public void start() { try { String url_string = "http://" + winsellahost + ":" + winsellaport + "/BrowserShare /viewerproxyservlet" + "?userid=viewer1&confid=ONE"; URL url = new URL(url_string); InputStream is = url.openConnection().getInputStream(); ObjectInputStream in = new ObjectInputStream(is); boolean firstTime = true; while (continueLoop) { show("5"); //Recve client screenshot and resize it to the current panel size ImageIcon imageIcon = (ImageIcon)in.readObject(); // in.reset(); Image image = imageIcon.getImage(); image = image.getScaledInstance(cPanel.getWidth(), cPanel.getHeight(), Image.SCALE_FAST); //Draw the received screenshot } in.close(); is.close(); } catch (IOException ex) { ex.printStackTrace(); } catch (ClassNotFoundException ex) { ex.printStackTrace(); } } </code></pre>

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