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  • Java: Tracking a user login session - Session EJBs vs HTTPSession

    - by bguiz
    If I want to keep track of a conversational state with each client using my web application, which is the better alternative - a Session Bean or a HTTP Session - to use? Using HTTP Session: //request is a variable of the class javax.servlet.http.HttpServletRequest //UserState is a POJO HttpSession session = request.getSession(true); UserState state = (UserState)(session.getAttribute("UserState")); if (state == null) { //create default value .. } String uid = state.getUID(); //now do things with the user id Using Session EJB: In the implementation of ServletContextListener registered as a Web Application Listener in WEB-INF/web.xml: //UserState NOT a POJO this this time, it is //the interface of the UserStateBean Stateful Session EJB @EJB private UserState userStateBean; public void contextInitialized(ServletContextEvent sce) { ServletContext servletContext = sce.getServletContext(); servletContext.setAttribute("UserState", userStateBean); ... In a JSP: public void jspInit() { UserState state = (UserState)(getServletContext().getAttribute("UserState")); ... } Elsewhere in the body of the same JSP: String uid = state.getUID(); //now do things with the user id It seems to me that the they are almost the same, with the main difference being that the UserState instance is being transported in the HttpRequest.HttpSession in the former, and in a ServletContext in the case of the latter. Which of the two methods is more robust, and why?

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  • How to profile object creation in Java?

    - by gooli
    The system I work with is creating a whole lot of objects and garbage collecting them all the time which results in a very steeply jagged graph of heap consumption. I would like to know which objects are being generated to tune the code, but I can't figure out a way to dump the heap at the moment the garbage collection starts. When I tried to initiate dumpHeap via JConsole manually at random times, I always got results after GC finished its run, and didn't get any useful data. Any notes on how to track down excessive temporary object creation are welcome.

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  • can not run java program from command line which resides in package

    - by kshitij
    See following code with resides in fillowing directory mypack.pack1 package mypack.pack1; public class myclass { public static void main(String args[]) { System.out.println("KKKKKKKKKKKKKKKKKKKKKKKKKKKKKK"); } } See following screen shot. that is giving error. And i dont want to add anything in class path because i am in particular directory and it has to work. why it is not working.??????

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  • How to pass checkbox array to Java from jsp

    - by eddy
    Hi, I'd like to know if there's any way to send data to the server for the selected rows using the checkboxes I've put on those rows? I mean , how can I send only the data of those selected rows to the server? Here's the html code I use: <table> <thead> <tr class="tableheader"> <td width="10%"></td> <td width="30%">Vehicle</td> <td width="40%">Driver</td> <td width="10%">Mileage</td> </tr> </thead> <tbody> <c:forEach items="${list}" var="item"> <tr> <td align="center"> <input type="checkbox" name="selectedItems" value="c:out value="${item.numberPlate}"/>"/> </td> <td align="left"><c:out value="${item.numberPlate}"/></td> <td align="left"><c:out value="${item.driver.fullName}" /></td> <td align="left"><input type="text" name="mileage" value="" /></td> </tr> </c:forEach> </tbody> </table> I really hope you can give some guidance on this. Thanks in beforehand.

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  • Java static method parameters

    - by Blitzkr1eg
    Why does the following code return 100 100 1 1 1 and not 100 1 1 1 1 ? public class Hotel { private int roomNr; public Hotel(int roomNr) { this.roomNr = roomNr; } public int getRoomNr() { return this.roomNr; } static Hotel doStuff(Hotel hotel) { hotel = new Hotel(1); return hotel; } public static void main(String args[]) { Hotel h1 = new Hotel(100); System.out.print(h1.getRoomNr() + " "); Hotel h2 = doStuff(h1); System.out.print(h1.getRoomNr() + " "); System.out.print(h2.getRoomNr() + " "); h1 = doStuff(h2); System.out.print(h1.getRoomNr() + " "); System.out.print(h2.getRoomNr() + " "); } } Why does it appear to pass Hotel by-value to doStuff() ?

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  • Getter/Setter (composition, Java, HW)

    - by Crystal
    I have one class called Person that basically looks like: public class Person { String firstName; String lastName; String telephone; String email; public Person() { firstName = ""; lastName = ""; telephone = ""; email = ""; } public Person(String firstName, String lastName, String telephone, String email) { this.firstName = firstName; this.lastName = lastName; this.telephone = telephone; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } .... Using that class, I setup an abstract class called Loan that looks like: public abstract class Loan { public void setClient(Person client) { this.client = client; } public Person getClient() { return client; } public void setLoanId(int nextId) { loanId = nextId; nextId++; } public int getLoanId() { return loanId; } public void setInterestRate(double interestRate) { this.interestRate = interestRate; } public double getInterestRate() { return interestRate; } public void setLoanLength(int loanLength) { this.loanLength = loanLength; } public int getLoanLength() { return loanLength; } public void setLoanAmount(double loanAmount) { this.loanAmount = loanAmount; } public double getLoanAmount(double loanAmount) { return loanAmount; } private Person client; private int loanId; private double interestRate; private int loanLength; private double loanAmount; private static int nextId = 1; } I have to extend the Loan class with CarLoan and it looks like: public class CarLoan extends Loan { public CarLoan(Person client, double vehiclePrice, double downPayment, double salesTax, double interestRate, CAR_LOAN_TERMS length) { super.setClient(client); super.setInterestRate(interestRate); this.client = client; this.vehiclePrice = vehiclePrice; this.downPayment = downPayment; this.salesTax = salesTax; this.length = length; } public void setVehiclePrice(double vehiclePrice) { this.vehiclePrice = vehiclePrice; } public double getVehiclePrice() { return vehiclePrice; } public void setDownPayment(double downPayment) { this.downPayment = downPayment; } public double getDownPayment() { return downPayment; } public void setSalesTax(double salesTax) { this.salesTax = salesTax; } public double getSalesTax() { return salesTax; } public String toString() { return getClass().getName() + "[vehiclePrice = " + vehiclePrice + '\n' + "downPayment = " + downPayment + '\n' + "salesTax = " + salesTax + "]"; } public enum CAR_LOAN_TERMS {TWO_YEAR, THREE_YEAR, SIX_YEAR}; private double vehiclePrice; private double downPayment; private double salesTax; Few questions. (a) Is what I did in the Loan class to setClient correct given what I have in the Person class? (e.g.this.client = client) (b) Can I call super twice in a method? I have to set two attributes from the Loan class from the constructor in the CarLoan class and I thought that would be a way to do it. (c) Do you have to set attributes for enumeration types differently in a constructor or getter/setter methods? I get an error for (this.length = length) in my CarLoan class and I was unsure of how enumeration values should be set. Thanks!

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  • Java Swing - Adding a row # column (row header) to a JTable

    - by llm
    I have data from a database loaded into a JTable through a custom table model. I want to have a column (should be the first column) which simply shows the display row number (i.e. it is not tied to any data (or sorting) but is simply the row number on the screen starting at 1). These "row headers" should be grayed out like the row headers. Any idea how to do this? Thanks

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  • Java - Calling all methods of a class

    - by Thomas Eschemann
    I'm currently working on an application that has to render several Freemarker templates. So far I have a Generator class that handles the rendering. The class looks more or less like this: public class Generator { public static void generate(…) { renderTemplate1(); renderTemplate2(); renderTemplate3(); } private static void render(…) { // renders the template } private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; private static void renderTemplate1() { // Create config object for the rendering // and calls render(); }; … } This works, but it doesn't really feel right. What I would like to do is create a class that holds all the renderTemplate...() methods and then call them dynamically from my Generator class. This would make it cleaner and easier to extend. I was thinking about using something like reflection, but it doesn't really feel like a good solution either. Any idea on how to implement this properly ?

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  • Formatting a byte array to string in java

    - by rgksugan
    I am using this code to find the MAC address of a machine.This code prints directly the MAC address, but i want to return it as a string.I am completely confused. please help. try { InetAddress add = InetAddress.getByName("10.123.96.102"); NetworkInterface ni1 = NetworkInterface.getByInetAddress(add); if (ni1 != null) { byte[] mac1 = ni1.getHardwareAddress(); if (mac1 != null) { for (int k = 0; k < mac1.length; k++) { System.out.format("%02X%s", mac1[k], (k < mac1.length - 1) ? "-" : ""); } } else { System.out.println("Address doesn't exist "); } System.out.println(); } else { System.out.println("address is not found."); } } catch (UnknownHostException e) { e.printStackTrace(); } catch (SocketException e) { e.printStackTrace(); }

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  • Java/Hibernate using interfaces over the entities.

    - by Dennetik
    I am using annoted Hibernate, and I'm wondering whether the following is possible. I have to set up a series of interfaces representing the objects that can be persisted, and an interface for the main database class containing several operations for persisting these objects (... an API for the database). Below that, I have to implement these interfaces, and persist them with Hibernate. So I'll have, for example: public interface Data { public String getSomeString(); public void setSomeString(String someString); } @Entity public class HbnData implements Data, Serializable { @Column(name = "some_string") private String someString; public String getSomeString() { return this.someString; } public void setSomeString(String someString) { this.someString = someString; } } Now, this works fine, sort of. The trouble comes when I want nested entities. The interface of what I'd want is easy enough: public interface HasData { public Data getSomeData(); public void setSomeData(Data someData); } But when I implement the class, I can follow the interface, as below, and get an error from Hibernate saying it doesn't know the class "Data". @Entity public class HbnHasData implements HasData, Serializable { @OneToOne(cascade = CascadeType.ALL) private Data someData; public Data getSomeData() { return this.someData; } public void setSomeData(Data someData) { this.someData = someData; } } The simple change would be to change the type from "Data" to "HbnData", but that would obviously break the interface implementation, and thus make the abstraction impossible. Can anyone explain to me how to implement this in a way that it will work with Hibernate?

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  • Strange Java Socket Behavior (Connects, but Doesn't Send)

    - by Donald Campbell
    I have a fairly complex project that boils down to a simple Client / Server communicating through object streams. Everything works flawlessly for two consecutive connections (I connect once, work, disconnect, then connect again, work, and disconnect). The client connects, does its business, and then closes. The server successfully closes both the object output stream and the socket, with no IO errors. When I try to connect a third time, the connection appears to go through (the ServerSocket.accept() method goes through and an ObjectOutputStream is successfully created). No data is passed, however. The inputStream.readUnshared() method simply blocks. I have taken the following memory precautions: When it comes time to close the sockets, all running threads are stopped, and all objects are nulled out. After every writeUnshared() method call, the ObjectOutputBuffer is flushed and reset. Has anyone encountered a similar problem, or does anyone have any suggestions? I'm afraid my project is rather large, and so copying code is problematic. The project boils down to this: SERVER MAIN ServerSocket serverSocket = new ServerSocket(port); while (true) { new WorkThread(serverSocket.accept()).start(); } WORK THREAD (SERVER) public void run() { ObjectInputBuffer inputBuffer = new ObjectInputBuffer(new BufferedInputStream(socket.getInputStream())); while (running) { try { Object myObject = inputBuffer.readUnshared(); // do work is not specified in this sample doWork(myObject); } catch (IOException e) { running = false; } } try { inputBuffer.close(); socket.close(); } catch (Exception e) { System.out.println("Could not close."); } } CLIENT public Client() { Object myObject; Socket mySocket = new Socket(address, port); try { ObjectOutputBuffer output = new ObjectOutputBuffer(new BufferedOutputStream(mySocket.getOutputStream())); output.reset(); output.flush(); } catch (Exception e) { System.out.println("Could not get an input."); mySocket.close(); return; } // get object data is not specified in this sample. it simply returns a serializable object myObject = getObjectData(); while (myObject != null) { try { output.writeUnshared(myObject); output.reset(); output.flush(); } catch (Exception e) { e.printStackTrace(); break; } // catch } // while try { output.close(); socket.close(); } catch (Exception e) { System.out.println("Could not close."); } } Thank you to everyone who may be able to help!

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  • Java: how to read BufferedReader faster

    - by Cata
    Hello, I want to optimize this code: InputStream is = rp.getEntity().getContent(); BufferedReader reader = new BufferedReader(new InputStreamReader(is)); String text = ""; String aux = ""; while ((aux = reader.readLine()) != null) { text += aux; } The thing is that i don't know how to read the content of the bufferedreader and copy it in a String faster than what I have above. I need to spend as little time as possible. Thank you

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  • Java reading xml element without prefix but within the scope of a namespace

    - by wsxedc
    Functionally, the two blocks should be the same <soapenv:Body> <ns1:login xmlns:ns1="urn:soap.sof.com"> <userInfo> <username>superuser</username> <password>qapass</password> </userInfo> </ns1:login> </soapenv:Body> ----------------------- <soapenv:Body> <ns1:login xmlns:ns1="urn:soap.sof.com"> <ns1:userInfo> <ns1:username>superuser</ns1:username> <ns1:password>qapass</ns1:password> </ns1:userInfo> </ns1:login> </soapenv:Body> However, how when I read using AXIS2 and I have tested it with java6 as well, I am having a problem. MessageFactory factory = MessageFactory.newInstance(); SOAPMessage soapMsg = factory.createMessage(new MimeHeaders(), SimpleTest.class.getResourceAsStream("LoginSoap.xml")); SOAPBody body = soapMsg.getSOAPBody(); NodeList nodeList = body.getElementsByTagNameNS("urn:soap.sof.com", "login"); System.out.println("Try to get login element" + nodeList.getLength()); // I can get the login element Node item = nodeList.item(0); NodeList elementsByTagNameNS = ((Element)item).getElementsByTagNameNS("urn:soap.sof.com", "username"); System.out.println("try to get username element " + elementsByTagNameNS.getLength()); So if I replace the 2nd getElementsByTagNameNS with ((Element)item).getElementsByTagName("username");, I am able to get the username element. Doesn't username have ns1 namespace even though it doesn't have the prefix? Am I suppose to keep track of the namespace scope to read an element? Wouldn't it became nasty if my xml elements are many level deep? Is there a workaround where I can read the element in ns1 namespace without knowing whether a prefix is defined?

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  • java programming

    - by Baiba
    ok i have version of t code, please tell me what i need to do when i need to get out of program The INDEX NUMBER OF COLUMN IN WHICH ARE LEAST ZEROS? class Uzd{ public static void main(String args[]){ int mas[][]= {{3,4,7,5,0}, {4,5,3,0,1}, {8,2,4,0,3}, {7,0,2,0,1}, {0,0,1,3,0}}; int nul_mas[] = new int[5]; int nul=0; for(int j=0;j<5;j++){// nul=0; for(int i=0;i<5;i++){ if(mas[i][j]==0){ nul++; } } nul_mas[j]=nul; } for(int i=0;i<5;i++){ for(int j=0;j<5;j++){ System.out.print(mas[i][j]); } System.out.println(); } System.out.println();// atstarpe System.out.println("///zeros in each column///"); for(int i=0;i<5;i++){System.out.print(nul_mas[i]);} System.out.println(); }} and after running it shows: 34750 45301 82403 70201 00130 ///zeros in each column/// But i need not in each column but i need to get out index of column in which zeros are least! in this situation it is column nubmer 2!! 12032

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  • Convert Java String to Array

    - by Bruce
    This is a weird problem. Here is my code String reply = listen.executeUrl("http://localhost:8080/JavaBridge/reply.php); executeUrl returns as String object whatever is returned by the reply.php file. Now comes the problem. In reply.php I am returning an PHP array and reply is a String. When I do System.out.println("Reply = "+reply); I get Reply = array(2) { [0]=> string(14) "Dushyant Arora" [1]=> string(19 ) "@dushyantarora13 hi"} But reply is still a String. How do I convert it into a String array or an Array.

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  • java will this threading setup work or what can i be doing wrong

    - by Erik
    Im a bit unsure and have to get advice. I have the: public class MyApp extends JFrame{ And from there i do; MyServer = new MyServer (this); MyServer.execute(); MyServer is a: public class MyServer extends SwingWorker<String, Object> { MyServer is doing listen_socket.accept() in the doInBackground() and on connection it create a new class Connection implements Runnable { I have the belove DbHelper that are a singleton. It holds an Sqlite connected. Im initiating it in the above MyApp and passing references all the way in to my runnable: class Connection implements Runnable { My question is what will happen if there are two simultaneous read or `write? My thought here was the all methods in the singleton are synchronized and would put all calls in the queue waiting to get a lock on the synchronized method. Will this work or what can i change? public final class DbHelper { private boolean initalized = false; private String HomePath = ""; private File DBFile; private static final String SYSTEM_TABLE = "systemtable"; Connection con = null; private Statement stmt; private static final ContentProviderHelper instance = new ContentProviderHelper (); public static ContentProviderHelper getInstance() { return instance; } private DbHelper () { if (!initalized) { initDB(); initalized = true; } } private void initDB() { DBFile = locateDBFile(); try { Class.forName("org.sqlite.JDBC"); // create a database connection con = DriverManager.getConnection("jdbc:sqlite:J:/workspace/workComputer/user_ptpp"); } catch (SQLException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } private File locateDBFile() { File f = null; try{ HomePath = System.getProperty("user.dir"); System.out.println("HomePath: " + HomePath); f = new File(HomePath + "/user_ptpp"); if (f.canRead()) return f; else { boolean success = f.createNewFile(); if (success) { System.out.println("File did not exist and was created " + HomePath); // File did not exist and was created } else { System.out.println("File already exists " + HomePath); // File already exists } } } catch (IOException e) { System.out.println("Maybe try a new directory. " + HomePath); //Maybe try a new directory. } return f; } public String getHomePath() { return HomePath; } private synchronized String getDate(){ SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); Date date = new Date(); return dateFormat.format(date); } public synchronized String getSelectedSystemTableColumn( String column) { String query = "select "+ column + " from " + SYSTEM_TABLE ; try { stmt = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY); ResultSet rs = stmt.executeQuery(query); while (rs.next()) { String value = rs.getString(column); if(value == null || value == "") return ""; else return value; } } catch (SQLException e ) { e.printStackTrace(); return ""; } finally { } return ""; } }

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  • java multiple operations depending on the type of the object passed

    - by mixm
    assuming i create a method which is passed an object, and that method would perform an action depending on the object passed. how should i identify the object? i thought of using the class name to identify the object, but may be impractical since i could easily change the class name of objects, and generate headaches during future development. am i right?

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  • Java - JPA - Generators - @SequenceGenerator

    - by Yatendra Goel
    I am learning JPA and have confusion in the @SequenceGenerator annotation. Upto my understanding, it automatically assigns a value to numeric identity fields/properties of an entity. Q1. Does this sequence generator make use of the database's increasing numeric value generating capability or generates the number on his own? Q2. If JPA uses database auto increement feauture, then will it work with datastores that don't have auto increement feature? Q3. If JPA generate numeric value on his own, then how the JPA implementation knows which value to generate next? Does it consult with the database first to see what value was stored last so as to generate the value (last + 1). ====================================================================================== Q4. Please also throw some light on sequenceName and allocationSize properties of @SequenceGenerator annotation.

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  • Extracting user-friendly exception details in Java

    - by Jon
    I've got a J2EE web application that I'm working on and when an exception occurs, I'd like to get some basic details about the exception and log it. The message that I'm logging should be pretty basic, something that might mean something to the people running the web server(s). Would using e.getMessage() be the best thing to log? Thanks.

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  • java number exceeds long.max_value - how to detect?

    - by jurchiks
    I'm having problems detecting if a sum/multiplication of two numbers exceeds the maximum value of a long integer. Example code: long a = 2 * Long.MAX_VALUE; System.out.println("long.max * smth > long.max... or is it? a=" + a); This gives me -2, while I would expect it to throw a NumberFormatException... Is there a simple way of making this work? Because I have some code that does multiplications in nested IF blocks or additions in a loop and I would hate to add more IFs to each IF or inside the loop. Edit: oh well, it seems that this answer from another question is the most appropriate for what I need: http://stackoverflow.com/a/9057367/540394 I don't want to do boxing/unboxing as it adds unnecassary overhead, and this way is very short, which is a huge plus to me. I'll just write two short functions to do these checks and return the min or max long. Edit2: here's the function for limiting a long to its min/max value according to the answer I linked to above: /** * @param a : one of the two numbers added/multiplied * @param b : the other of the two numbers * @param c : the result of the addition/multiplication * @return the minimum or maximum value of a long integer if addition/multiplication of a and b is less than Long.MIN_VALUE or more than Long.MAX_VALUE */ public static long limitLong(long a, long b, long c) { return (((a > 0) && (b > 0) && (c <= 0)) ? Long.MAX_VALUE : (((a < 0) && (b < 0) && (c >= 0)) ? Long.MIN_VALUE : c)); } Tell me if you think this is wrong.

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  • Recursive Enumeration in Java

    - by Harm De Weirdt
    Hello everyone. I still have a question about Enumerations. Here's a quick sketch of the situation. I have a class Backpack that has a Hashmap content with as keys a variable of type long, and as value an ArrayList with Items. I have to write an Enumeration that iterates over the content of a Backpack. But here's the catch: in a Backpack, there can also be another Backpack. And the Enumeration should also be able to iterate over the content of a backpack that is in the backpack. (I hope you can follow, I'm not really good at explaining..) Here is the code I have: public Enumeration<Object> getEnumeration() { return new Enumeration<Object>() { private int itemsDone = 0; //I make a new array with all the values of the HashMap, so I can use //them in nextElement() Collection<Long> keysCollection = getContent().keySet(); Long [] keys = keysCollection.toArray(new Long[keysCollection.size()]); public boolean hasMoreElements() { if(itemsDone < getContent().size()) { return true; }else { return false; } } public Object nextElement() { ArrayList<Item> temporaryList= getContent().get(keys[itemsDone]); for(int i = 0; i < temporaryList.size(); i++) { if(temporaryList.get(i) instanceof Backpack) { return temporaryList.get(i).getEnumeration(); }else { return getContent().get(keys[itemsDone++]); } } } }; Will this code work decently? It's just the "return temporaryList.get(i).getEnumeration();" I'm worried about. Will the users still be able to use just the hasMoreElemens() and nextElement() like he would normally do? Any help is appreciated, Harm De Weirdt

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