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  • Servlet that starts a thread only once for every visitor

    - by user858749
    Hey I want to implement a Java Servlet that starts a thread only once for every single user. Even on refresh it should not start again. My last approach brought me some trouble so no code^^. Any Suggestions for the layout of the servlet? public class LoaderServlet extends HttpServlet { // The thread to load the needed information private LoaderThread loader; // The last.fm account private String lfmaccount; public LoaderServlet() { super(); lfmaccount = ""; } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { if (loader != null) { response.setContentType("text/plain"); response.setHeader("Cache-Control", "no-cache"); PrintWriter out = response.getWriter(); out.write(loader.getStatus()); out.flush(); out.close(); } else { loader = new LoaderThread(lfmaccount); loader.start(); request.getRequestDispatcher("WEB-INF/pages/loader.jsp").forward( request, response); } } @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { if (lfmaccount.isEmpty()) { lfmaccount = request.getSession().getAttribute("lfmUser") .toString(); } request.getRequestDispatcher("WEB-INF/pages/loader.jsp").forward( request, response); } } The jsp uses ajax to regularly post to the servlet and get the status. The thread just runs like 3 minutes, crawling some last.fm data.

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  • How can I get an image too big from a server?

    - by Daniel Calderon Mori
    I'm currenty developing for blackberry and just bumped into this problem as i was trying to download an image from a server. The servlet which the device communicates with is working correctly, as I have made a number of tests for it. But it gives me the 413 HTTP error ("Request entity too large"). I figure i will just get the bytes, uhm, portion by portion. How can i accomplish this? This is the code of the servlet (the doGet() method): try { ImageIcon imageIcon = new ImageIcon("c:\\Users\\dcalderon\\prueba.png"); Image image = imageIcon.getImage(); PngEncoder pngEncoder = new PngEncoder(image, true); output.write(pngEncoder.pngEncode()); } finally { output.close(); } Thanks. It's worth mentioning that I am developing both the client-side and the server-side.

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  • Java: Convenient way to refactor the application.

    - by Harshal
    Hi, Everyone We have an agile enterprise application built on JSP and Servlet without any design strategy. This application was built in early 2002 considering 1000 users. After 2002, we received lots of requests from the marketing partners. Currently, the application has lots of spaghetti code with lots of Ifs and elses. One class has more than 20,000 lines of code with a huge body of functions without abstraction. Now, we need to support billions of records, what we need to do immediately and gradually? We have to refactor the application? Which framework, we need to use? How the usage of the framework will be helpful to the end users? How to convince the leaders to do the refactoring? How to gain the faster response time as compare to the current system?

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  • FileNotFound exception

    - by Pratik
    I am trying to read a file in a servlet. I am using eclipse IDE. I get a FileNotFoundException if I provide relative file name. List<String> ls=new ArrayList<String>(); Scanner input = new Scanner(new File("Input.txt")); while(input.hasNextLine()) { ls.add(input.nextLine()); } The same code works if I put the absolute path like this: Scanner input = new Scanner(new File("F:/Spring and other stuff/AjaxDemo/src/com/pdd/ajax/Input.txt")); The Java file and text file are there in the same folder. Does it searches text file in some other folder ?

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  • Handling file upload in a non-blocking manner

    - by Kaliyug Antagonist
    The background thread is here Just to make objective clear - the user will upload a large file and must be redirected immediately to another page for proceeding different operations. But the file being large, will take time to be read from the controller's InputStream. So I unwillingly decided to fork a new Thread to handle this I/O. The code is as follows : The controller servlet /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse * response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub System.out.println("In Controller.doPost(...)"); TempModel tempModel = new TempModel(); tempModel.uploadSegYFile(request, response); System.out.println("Forwarding to Accepted.jsp"); /*try { Thread.sleep(1000 * 60); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); }*/ request.getRequestDispatcher("/jsp/Accepted.jsp").forward(request, response); } The model class package com.model; import java.io.IOException; import java.util.concurrent.ExecutionException; import java.util.concurrent.Future; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.utils.ProcessUtils; public class TempModel { public void uploadSegYFile(HttpServletRequest request, HttpServletResponse response) { // TODO Auto-generated method stub System.out.println("In TempModel.uploadSegYFile(...)"); /* * Trigger the upload/processing code in a thread, return immediately * and notify when the thread completes */ try { FileUploaderRunnable fileUploadRunnable = new FileUploaderRunnable( request.getInputStream()); /* * Future<FileUploaderRunnable> future = ProcessUtils.submitTask( * fileUploadRunnable, fileUploadRunnable); * * FileUploaderRunnable processed = future.get(); * * System.out.println("Is file uploaded : " + * processed.isFileUploaded()); */ Thread uploadThread = new Thread(fileUploadRunnable); uploadThread.start(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } /* * catch (InterruptedException e) { // TODO Auto-generated catch block * e.printStackTrace(); } catch (ExecutionException e) { // TODO * Auto-generated catch block e.printStackTrace(); } */ System.out.println("Returning from TempModel.uploadSegYFile(...)"); } } The Runnable package com.model; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.nio.ByteBuffer; import java.nio.channels.Channels; import java.nio.channels.ReadableByteChannel; public class FileUploaderRunnable implements Runnable { private boolean isFileUploaded = false; private InputStream inputStream = null; public FileUploaderRunnable(InputStream inputStream) { // TODO Auto-generated constructor stub this.inputStream = inputStream; } public void run() { // TODO Auto-generated method stub /* Read from InputStream. If success, set isFileUploaded = true */ System.out.println("Starting upload in a thread"); File outputFile = new File("D:/06c01_output.seg");/* * This will be changed * later */ FileOutputStream fos; ReadableByteChannel readable = Channels.newChannel(inputStream); ByteBuffer buffer = ByteBuffer.allocate(1000000); try { fos = new FileOutputStream(outputFile); while (readable.read(buffer) != -1) { fos.write(buffer.array()); buffer.clear(); } fos.flush(); fos.close(); readable.close(); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println("File upload thread completed"); } public boolean isFileUploaded() { return isFileUploaded; } } My queries/doubts : Spawning threads manually from the Servlet makes sense to me logically but scares me coding wise - the container isn't aware of these threads after all(I think so!) The current code is giving an Exception which is quite obvious - the stream is inaccessible as the doPost(...) method returns before the run() method completes : In Controller.doPost(...) In TempModel.uploadSegYFile(...) Returning from TempModel.uploadSegYFile(...) Forwarding to Accepted.jsp Starting upload in a thread Exception in thread "Thread-4" java.lang.NullPointerException at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:512) at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:497) at org.apache.coyote.http11.InternalInputBuffer$InputStreamInputBuffer.doRead(InternalInputBuffer.java:559) at org.apache.coyote.http11.AbstractInputBuffer.doRead(AbstractInputBuffer.java:324) at org.apache.coyote.Request.doRead(Request.java:422) at org.apache.catalina.connector.InputBuffer.realReadBytes(InputBuffer.java:287) at org.apache.tomcat.util.buf.ByteChunk.substract(ByteChunk.java:407) at org.apache.catalina.connector.InputBuffer.read(InputBuffer.java:310) at org.apache.catalina.connector.CoyoteInputStream.read(CoyoteInputStream.java:202) at java.nio.channels.Channels$ReadableByteChannelImpl.read(Unknown Source) at com.model.FileUploaderRunnable.run(FileUploaderRunnable.java:39) at java.lang.Thread.run(Unknown Source) Keeping in mind the point 1., does the use of Executor framework help me in anyway ? package com.utils; import java.util.concurrent.Future; import java.util.concurrent.ScheduledThreadPoolExecutor; public final class ProcessUtils { /* Ensure that no more than 2 uploads,processing req. are allowed */ private static final ScheduledThreadPoolExecutor threadPoolExec = new ScheduledThreadPoolExecutor( 2); public static <T> Future<T> submitTask(Runnable task, T result) { return threadPoolExec.submit(task, result); } } So how should I ensure that the user doesn't block and the stream remains accessible so that the (uploaded)file can be read from it?

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  • Servlet doesnt appear to execute in a threaded manner

    - by RenegadeAndy
    I have developed a simple server using Tomcat which runs a servlet. The servlet calls a command line program - which takes about 20 seconds to execute then returns the result to the user via JSON. The problem is - if i make above 2 simultaneous requests, the servlet blocks until one of the previous requests is completed. An example of this can be seen below - "Im in" is the top of the servlet, and the list of results is after the servlet is executed. All requests were made at the same time - but you can clearly see they are not dealt with simultaneously. What setting do I need to change in tomcat in order to have all requests handeled at the same time? Thanks Andy Im in Im in FVFNT01 STOP_IDLE FVFNT03 STOP_IDLE FVFNT16 STOP_IDLE FVFNT17 STOP_IDLE FVFNT01 STOP_IDLE FVFNT03 STOP_IDLE FVFNT16 STOP_IDLE FVFNT17 STOP_IDLE Im in FVFNT01 STOP_IDLE FVFNT03 STOP_IDLE FVFNT16 STOP_IDLE FVFNT17 STOP_IDLE Im in FVFNT01 STOP_IDLE FVFNT03 STOP_IDLE FVFNT16 STOP_IDLE FVFNT17 STOP_IDLE Im in FVFNT01 STOP_IDLE FVFNT03 STOP_IDLE FVFNT16 STOP_IDLE FVFNT17 STOP_IDLE Im in FVFNT01 STOP_IDLE FVFNT03 STOP_IDLE FVFNT16 STOP_IDLE FVFNT17 STOP_IDLE Im in FVFNT01 STOP_IDLE FVFNT03 STOP_IDLE FVFNT16 STOP_IDLE FVFNT17 STOP_IDLE Im in FVFNT01 STOP_IDLE FVFNT03 STOP_IDLE FVFNT16 STOP_IDLE FVFNT17 STOP_IDLE

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  • How to explicitly terminate http connection from server with no response header

    - by Gagandip
    I am developing a server simulator for one of my client application. I am using GlassFish server. I have to simulate a http connection terminate condition in my server application. Is there a way by which I can explicitly terminate a connection from server side such that client does not receive any response header. Currently I have tried many options like closing the response outputStream. But in every case a http 200 OK message is delivered to the client application. I would like to consume the http-request and do not want to return anything to the client. I am using a simple conrtroller servlet and had overridden doGet() and doPost() functions.

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  • JSP getParameter problem

    - by user236501
    I have a form, if the timer reach the form will auto redirect to the Servlet to update database. My problem now is if javascript redirect the window to servlet my request.getParameter is null. function verify(f,whichCase){ if(whichCase == "Submit"){ msg = "Are you sure that you want to submit this test?"; var i = confirm(msg) if(i){ parent.window.location = "sindex.jsp" } return i; } } I doing this because i got a iframe in my jsp. Timer update problem have to use iframe. So, when time up or user click submit parent.window.location can let me refresh parent window <form method="POST" action="${pageContext.request.contextPath}/TestServlet" onSubmit="return verify(this,whichPressed)"> My form when user click submit button within the timing, it will trigger the verify function to let user confirm submit. So inside my TestServlet i got this, because using javascript redirect request.getParameter("answer") this keep return me null. protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { if (request.getParameter("Submit") != null) { String ans = request.getParameter("answer"); Answer a = new Answer(ans, no); aa.CreateAnswer(an,t.getTestCode(),username); RequestDispatcher rd = request.getRequestDispatcher("/sindex.jsp"); rd.forward(request, response); } } Below are my timer when time up redirect to TestServlet trigger the doGet method if((mins == 0) && (secs == 0)) { window.alert("Time is up. Press OK to submit the test."); // change timeout message as required var sUrl = "TestServlet"; parent.window.location = sUrl // redirects to specified page once timer ends and ok button is pressed } else { cd = setTimeout("redo()",1000); }

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  • dao as a member of a servlet - normal?

    - by EugeneP
    I guess, DAO is thread safe, does not use any class members. So can it be used without any problem as a private field of a Servlet ? We need only one copy, and multiple threads can access it simultaneously, so why bother creating a local variable, right?

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  • How to get the action from the HttpServlet request to dispatch to multiple pages

    - by JFB
    I am using the Page Controller pattern. How could I use the same controller for two different pages by detecting the request action and then dispatching according to the result? Here is my code: account.jsp <form name="input" action="<%=request.getContextPath() %>/edit" method="get"> <input type="submit" value="Modifier" /> </form> Account Servlet public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println("received HTTP GET"); String action = request.getParameter("action"); if (action == null) { // the account page dispatch(request, response, "/account"); } else if (action == "/edit") { // the popup edit page dispatch(request, response, "/edit"); } protected void dispatch(HttpServletRequest request, HttpServletResponse response, String page) throws javax.servlet.ServletException, java.io.IOException { RequestDispatcher dispatcher = getServletContext() .getRequestDispatcher(page); dispatcher.forward(request, response); } }

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  • ApplicationDispatcher exception

    - by JFB
    Whenever I try to redirect to a certain page using this dispatch method that is called from my doGet method, I get the following exception. I have no idea why! account controller servlet protected void dispatch(HttpServletRequest request, HttpServletResponse response, String page) throws javax.servlet.ServletException, java.io.IOException { RequestDispatcher dispatcher = getServletContext() .getRequestDispatcher(page); try { dispatcher.forward(request, response); } catch (java.lang.NullPointerException e) { System.out.println("NullPointerException: attribute expected in view"); } } Error msg java.lang.NullPointerException org.apache.jasper.JasperException: java.lang.NullPointerException org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:502) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:430) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) controller.AccountController.dispatch(AccountController.java:91) controller.AccountController.doExecute(AccountController.java:72) controller.AccountController.doGet(AccountController.java:34) javax.servlet.http.HttpServlet.service(HttpServlet.java:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) java.lang.NullPointerException org.apache.jsp.content.edit_jsp._jspService(edit_jsp.java:109) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) controller.AccountController.dispatch(AccountController.java:91) controller.AccountController.doExecute(AccountController.java:72) controller.AccountController.doGet(AccountController.java:34) javax.servlet.http.HttpServlet.service(HttpServlet.java:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

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  • Sending XML to Servlet from Action Script

    - by John Doe
    I am only getting empty arrays on output. Anyone know what Exactly I'm doing wrong? package myDungeonAccessor; /* * To change this template, choose Tools | Templates * and open the template in the editor. */ import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class myDungeonAccessorServlet extends HttpServlet { private myDungeonAccessor dataAccessor; /** * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods. * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); try { /* TODO output your page here out.println("<html>"); out.println("<head>"); out.println("<title>Servlet myDungeonAccessorServlet</title>"); out.println("</head>"); out.println("<body>"); out.println("<h1>Servlet myDungeonAccessorServlet at " + request.getContextPath () + "</h1>"); out.println("</body>"); out.println("</html>"); */ } finally { out.close(); } } // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code."> /** * Handles the HTTP <code>GET</code> method. * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); // PrintWriter out = response.getWriter(); System.out.println("yo mom"); } /** * Handles the HTTP <code>POST</code> method. * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //System.out.println("heppo"); //dataAccessor = new myDungeonAccessor(); System.out.println("Hello"); try { System.out.println("HEADERS: " + request.getHeaderNames()); ObjectInputStream in = new ObjectInputStream(request.getInputStream()); ObjectOutputStream out = new ObjectOutputStream(response.getOutputStream()); } catch(Exception e) { e.printStackTrace(); } System.out.println("WAZZUP"); byte [] buffer = new byte[4096]; //in.read(buffer); System.out.println("TEST!"); String s = new String(buffer); System.out.println("Update S:" + s); } /** * Returns a short description of the servlet. * @return a String containing servlet description */ @Override public String getServletInfo() { return "Short description"; } }

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  • Not able to connect the DB from Servlet

    - by user1885127
    I have started jsp servlet application with Xampp Server, In which I have dbconnection.java and LoginValidator.java (servlet) files. I'm getting an error while trying to access the database from servlet (LoginValidator.java). It is getting the following error: Class Not found Exception : com.mysql.jdbc.Driver I have imported the mysql-connector-java-5.1.18-bin.jar. I have searched a lot but could not find the solution.

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  • Set request attributes when a Form is POSTed

    - by ssahmed555
    Is there any way to set request attributes (not parameters) when a form is posted? The problem I am trying to solve is: I have a JSP page displaying some data in a couple of dropdown lists. When the form is posted, my Controller servlet processes this request (based on the parameters set/specified in the form) and redirects to the same JSP page that is supposed to display addition details. I now want to display the same/earlier data in the dropdown lists without having to recompute or recalculate to get that same data. And in the said JSP page, the dropdown lists in the form are populated by data that is specified through request attributes. Right now, after the Form is POSTed and I am redirected to the same JSP page the dropdown lists are empty because the necessary request attributes are not present. I am quite the n00b when it comes to web apps, so an obvious & easy solution to this problem escapes me at the moment! I am open to suggestions on how to restructure the control flow in the Servlet. Some details about this app: standard Servlet + JSP, JSTL, running in Apache Tomcat 6.0. Thanks.

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  • Can I write a module/filter that gets fired before the web app get's run in Tomcat?

    - by Blankman
    Can I write a module/filter that gets put into the processing pipleline in Tomcat BEFORE the web application even gets run? Something that I could turn on/off for each web application that tomcat is handling. is this possible? So basically it would be a re-usable filter that hooks into the web pipeline that could alter the requests behavior or perform/modify the requests. One example would be to log all ip's, or redirect based on the url, block the request, etc.

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  • How to add response headers based on Content-type; getting Content-type before the response is commi

    - by Bozho
    I want to set the Expires header for all image/* and text/css. I'm doing this in a Filter. However: before calling chain.doFilter(..) the Content-type is not yet "realized" after calling chain.doFilter(..) the Content-type is set, but so is content-length, which forbids adding new headers (at least in Tomcat implementation) I can use the extensions of the requested resource, but since some of the css files are generated by richfaces by taking them from inside jar-files, the name of the file isn't x.css, but is /xx/yy/zz.xcss/DATB/.... So, is there a way to get the Content-type before the response is committed.

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  • servlet stops working with tomcat server after some hits or time

    - by nekin
    hi all i have very strange issue with some of my servlet. below is my configuration Folder A is having X number os servelet deployed in tomcat directory Folder B is having Y number of servelet deployed in tomcat directory. now after certain amount of time or hits to any of the servelet in Folder B is stops working properly, whereas at same time All servelet of Folder A works fine i am not able to trace where i am doing mistake all coding for both folder's servelet is same only difference is they are with different dB, but it is very simple read only operation with dB though. any idea ? thks

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  • Does a servlet knows the encoding of the sent form that specified using http-equiv?

    - by Daziplqa
    Does a servlet knows the encoding of the sent form that specified using http-equiv? When I specify an encoding of a POSTed form using http-equiv like that: <HTML> <head> <meta http-equiv='Content-Type' content='text/html; charset=gb2312'/> </head> <BODY > <form name="form" method="post" > <input type="text" name="v_rcvname" value="????"> </form> </BODY> </HTML> And then at the servlet I use the method, request.getCharacterEncoding() I got null ! So, Is there a way that I can tell the server that I am encoding the data in some char encoding??

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