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• What's the best way to store Logon User information for Web Application?

  - by Morgan Cheng

  I was once in a project of web application developed on ASP.NET. For each logon user, there is an object (let's call it UserSessionObject here) created and stored in RAM. For each HTTP request of given user, matching UserSessoinObject instance is used to visit user state information and connection to database. So, this UserSessionObject is pretty important. This design brings several problems found later: 1) Since this UserSessionObject is cached in ASP.NET memory space, we have to config load balancer to be sticky connection. That is, HTTP request in single session would always be sent to one web server behind. This limit scalability and maintainability. 2) This UserSessionObject is accessed in every HTTP request. To keep the consistency, there is a exclusive lock for the UserSessionObject. Only one HTTP request can be processed at any given time because it must to obtain the lock first. The performance and response time is affected. Now, I'm wondering whether there is better design to handle such logon user case. It seems Sharing-Nothing-Architecture helps. That means long user info is retrieved from database each time. I'm afraid that would hurt performance. Is there any design pattern for long user web app? Thanks.

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• using strcpy_s for TCHAR pointer (Microsoft Specific)

  - by Yan Cheng CHEOK

  I was wondering which is the correct way? _tcscpy(tchar_pointer, _tcslen(tchar_pointer), _T("Hello World")); or _tcscpy(tchar_pointer, _tcsclen(tchar_pointer), _T("Hello World")); or _tcscpy(tchar_pointer, ???, _T("Hello World"));

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• Is it possible to listen to relational database update?

  - by Morgan Cheng

  Is it possible to listen to relation database update? For example, my web app want to send data update to client through Comet technology. I can have the program to poll the database periodically, but that would not be performant and scalable. If app can hood to a "event handler" of database, then app can get notification every time given database table data is updated. This sounds more promising, but I didn't find any concrete example for it. This is listener pattern. Does common relational database support such feature?

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• How to implement a collection (list, map?) of complicated strings in Java?

  - by Alex Cheng

  Hi all. I'm new here. Problem -- I have something like the following entries, 1000 of them: args1=msg args2=flow args3=content args4=depth args6=within ==> args5=content args1=msg args2=flow args3=content args4=depth args6=within args7=distance ==> args5=content args1=msg args2=flow args3=content args6=within ==> args5=content args1=msg args2=flow args3=content args6=within args7=distance ==> args5=content args1=msg args2=flow args3=flow ==> args4=flowbits args1=msg args2=flow args3=flow args5=content ==> args4=flowbits args1=msg args2=flow args3=flow args6=depth ==> args4=flowbits args1=msg args2=flow args3=flow args6=depth ==> args5=content args1=msg args2=flow args4=depth ==> args3=content args1=msg args2=flow args4=depth args5=content ==> args3=content args1=msg args2=flow args4=depth args5=content args6=within ==> args3=content args1=msg args2=flow args4=depth args5=content args6=within args7=distance ==> args3=content I'm doing some sort of suggestion method. Say, args1=msg args2=flow args3=flow == args4=flowbits If the sentence contains msg, flow, and another flow, then I should return the suggestion of flowbits. How can I go around doing it? I know I should scan (whenever a character is pressed on the textarea) a list or array for a match and return the result, but, 1000 entries, how should I implement it? I'm thinking of HashMap, but can I do something like this? <"msg,flow,flow","flowbits" Also, in a sentence the arguments might not be in order, so assuming that it's flow,flow,msg then I can't match anything in the HashMap as the key is "msg,flow,flow". What should I do in this case? Please help. Thanks a million!

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• How can i handle mouse double click event on textbox?

  - by Kar Cheng

  Hello, I want to open one child window on mouse double click of textbox. I know the only event available in Silverlight is MouseLeftButtonDown and you have to simulate double click. However it still doesn't work when i click in the middle of the textbox. It only works when i double click on the border of the textbox. Anybody has any ideas of how can i do this? If any 3rd party library is available then also it's fine. Thanks in advance:)

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• AtomicInteger lazySet and set

  - by Yan Cheng CHEOK

  May I know what is the difference among lazySet and set method for AtomicInteger. javadoc doesn't talk much about lazySet : Eventually sets to the given value. It seems that AtomicInteger will not immediately be set to the desired value, but it will be scheduled to be set in some time. But, what is the practical use of this method? Any example?

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• Usage of VIsual Memory Leak Detector

  - by Yan Cheng CHEOK

  I found a very interesting memory leak detector by using Visual C++. http://www.codeproject.com/KB/applications/visualleakdetector.aspx I try it out, but cannot make it works to detect a memory leak code. I am using MS Visual Studio 2008. Any step I had missed out? #include "stdafx.h" #include "vld.h" #include <iostream> void fun() { new int[1000]; } int _tmain(int argc, _TCHAR* argv[]) { fun(); std::cout << "lead?" << std::endl; getchar(); return 0; } The output when I run in debug mode is : ... ... 'Test.exe': Loaded 'C:\WINDOWS\WinSxS\x86_Microsoft.VC80.CRT_1fc8b3b9a1e18e3b_8.0.50727.4053_x-ww_e6967989\msvcr80.dll', Symbols loaded. 'Test.exe': Loaded 'C:\WINDOWS\system32\msvcrt.dll', Symbols loaded (source information stripped). 'Test.exe': Loaded 'C:\WINDOWS\WinSxS\x86_Microsoft.VC90.DebugCRT_1fc8b3b9a1e18e3b_9.0.30729.1_x-ww_f863c71f\msvcp90d.dll', Symbols loaded. 'Test.exe': Loaded 'C:\Program Files\Visual Leak Detector\bin\dbghelp.dll', Symbols loaded (source information stripped). Visual Leak Detector Version 1.9d installed. No memory leaks detected. Visual Leak Detector is now exiting. The program '[5468] Test.exe: Native' has exited with code 0 (0x0).

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• xstream handles non-english character

  - by Yan Cheng CHEOK

  I have the following code : /* * To change this template, choose Tools | Templates * and open the template in the editor. */ package helloworld; import com.thoughtworks.xstream.XStream; import java.io.File; import java.io.FileOutputStream; import java.io.InputStream; import java.io.OutputStream; import javax.swing.JOptionPane; /** * * @author yccheok */ public class Test { @SuppressWarnings("unchecked") public static <A> A fromXML(Class c, File file) { XStream xStream = new XStream(); InputStream inputStream = null; try { inputStream = new java.io.FileInputStream(file); Object object = xStream.fromXML(inputStream); if (c.isInstance(object)) { return (A)object; } } catch (Exception exp) { exp.printStackTrace(); } finally { if (inputStream != null) { try { inputStream.close(); inputStream = null; } catch (java.io.IOException exp) { exp.printStackTrace(); return null; } } } return null; } @SuppressWarnings("unchecked") public static <A> A fromXML(Class c, String filePath) { return (A)fromXML(c, new File(filePath)); } public static boolean toXML(Object object, File file) { XStream xStream = new XStream(); OutputStream outputStream = null; try { outputStream = new FileOutputStream(file); xStream.toXML(object, outputStream); } catch (Exception exp) { exp.printStackTrace(); return false; } finally { if (outputStream != null) { try { outputStream.close(); outputStream = null; } catch (java.io.IOException exp) { exp.printStackTrace(); return false; } } } return true; } public static boolean toXML(Object object, String filePath) { return toXML(object, new File(filePath)); } public static void main(String args[]) { String s = "\u6210\u4EA4\u91CF"; // print ??? System.out.println(s); // fine! show ??? JOptionPane.showMessageDialog(null, s); toXML(s, "C:\\A.XML"); String o = fromXML(String.class, "C:\\A.XML"); // show ??? JOptionPane.showMessageDialog(null, o); } } I run the following code through command prompt in Windows Vista. 1) May I know why System.out.println unable to print out Chinese Character in console? 2) I open up the xstream file. The saved value is <string>???</string> How can I make xstream save Chinese Character correctly? Thanks.

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• What requests do browsers' "F5" and "Ctrl + F5" refreshes generate?

  - by Morgan Cheng

  Is there a standard for what actions F5 and Ctrl+F5 trigger in web browsers? I once did experiment in IE6 and Firefox 2.x. The "F5" refresh would trigger a HTTP request sent to the server with an "If-Modified-Since" header, while "Ctrl+F5" would not have such a header. In my understanding, F5 will try to utilize cached content as much as possible, while "Ctrl+F5" is intended to abandon all cached content and just retrieve all content from the servers again. But today, I noticed that in some of the latest browsers (Chrome, IE8) it doesn't work in this way anymore. Both "F5" and "Ctrl+F5" send the "If-Modified-Since" header. So how is this supposed to work, or (if there is no standard) how do the major browsers differ in how they implement these refresh features?

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• Is this the intention behavior in JComboBox? How I can avoid this behavior?

  - by Yan Cheng CHEOK

  I realize that if you are having a same selection in JComboBox, using up/down arrow key, will not help you to navigate the selection around. How I can avoid this behavior? See the below screen shoot /* * To change this template, choose Tools | Templates * and open the template in the editor. */ /* * NewJFrame.java * * Created on May 8, 2010, 7:46:28 PM */ package javaapplication26; /** * * @author yccheok */ public class NewJFrame extends javax.swing.JFrame { /** Creates new form NewJFrame */ public NewJFrame() { initComponents(); /* If you are having 3 same strings here. Using, up/down arrow key, * will not move the selection around. */ this.jComboBox1.addItem("Intel"); this.jComboBox1.addItem("Intel"); this.jComboBox1.addItem("Intel"); } /** This method is called from within the constructor to * initialize the form. * WARNING: Do NOT modify this code. The content of this method is * always regenerated by the Form Editor. */ @SuppressWarnings("unchecked") // <editor-fold defaultstate="collapsed" desc="Generated Code"> private void initComponents() { jComboBox1 = new javax.swing.JComboBox(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); jComboBox1.setEditable(true); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); getContentPane().setLayout(layout); layout.setHorizontalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(105, 105, 105) .addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, 158, javax.swing.GroupLayout.PREFERRED_SIZE) .addContainerGap(137, Short.MAX_VALUE)) ); layout.setVerticalGroup( layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGroup(layout.createSequentialGroup() .addGap(63, 63, 63) .addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) .addContainerGap(217, Short.MAX_VALUE)) ); pack(); }// </editor-fold> /** * @param args the command line arguments */ public static void main(String args[]) { java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new NewJFrame().setVisible(true); } }); } // Variables declaration - do not modify private javax.swing.JComboBox jComboBox1; // End of variables declaration }

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• Is this a correct way to stop Execution Task

  - by Yan Cheng CHEOK

  I came across code to stop execution's task. private final ExecutorService executor = Executors.newSingleThreadExecutor(); public void stop() { executor.shutdownNow(); try { executor.awaitTermination(100, TimeUnit.DAYS); } catch (InterruptedException ex) { log.error(null, ex); } } public Runnable getRunnable() { return new Runnable() { public void run() { while (!Thread.currentThread().isInterrupted()) { // What if inside fun(), someone try to clear the interrupt flag? // Say, through Thread.interrupted(). We will stuck in this loop // forever. fun(); } } }; } I realize that, it is possible for Runnable to be in forever loop, as Unknown fun may Thread.sleep, clear the interrupt flag and ignore the InterruptedException Unknown fun may Thread.interrupted, clear the interrupt flag. I was wondering, is the following way correct way to fix the code? private final ExecutorService executor = Executors.newSingleThreadExecutor(); private volatile boolean flag = true; public void stop() { flag = false; executor.shutdownNow(); try { executor.awaitTermination(100, TimeUnit.DAYS); } catch (InterruptedException ex) { log.error(null, ex); } } public Runnable getRunnable() { return new Runnable() { public void run() { while (flag && !Thread.currentThread().isInterrupted()) { // What if inside fun(), someone try to clear the interrupt flag? // Say, through Thread.interrupted(). We will stuck in this loop // forever. fun(); } } }; }

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• How to invoke static method in C#4.0 with dynamic type?

  - by Morgan Cheng

  In C#4.0, we have dynamic type, but how to invoke static method of dynamic type object? Below code will generate exception at run time. class Foo { public static int Sum(int x, int y) { return x + y; } } class Program { static void Main(string[] args) { dynamic d = new Foo(); Console.WriteLine(d.Sum(1, 3)); } } IMHO, dynamic is invented to bridge C# and other programming language. There is some other language (e.g. Java) allows to invoke static method through object instead of type. BTW, The introduction of C#4.0 is not so impressive compared to C#3.0.

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• Getting batch_action functionality in Symfony 1.0

  - by Alex Ciminian

  I'm currently working on a web app written in Symfony. I'm supposed to add an "export to CSV" feature in the backend/administration part of the app for some modules. In the list view, there should be an "Export" button which should provide the user with a csv file of the elements that are displayed (considering filtering criteria). I've created a method in the actions class of the module that takes a comma separated list of ids and generates the CSV, but I'm not really sure how to add the link to it in the view. The problem is that the view doesn't exist anywhere, it's generated on the fly from the data in the generator.yml configuration file. I've posted the relevant part of the file below. I'm new to Symfony, so any help would be appreciated :). Thanks, Alex Update list: display: [id, =name, indemn, _status, _participants, _approved_, created_at] title: Lista actiuni object_actions: _edit: ~ _delete: ~ actions: _create: ~ export_csv: name: Export to CSV action: CSVExport params: id=csvActionSubmit filters: [name, county_id, _status_filter, activity_id] fields: id: name: Nr. crt. ... Thanks to your advice, I've managed to add a button that is linked to my action. The problem is that I also need to send some parameters to the action, because I may not want all the elements - filters may have been used. Unfortunately, the project is using Symfony 1.0, which doesn't support batch_actions. Currently, I'm working around this with Javascript (I parse the DOM to get the numeric ids (from the display table) and then build the link for the button. I really think there could be a better way for this.

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• vagrant box add: where does .box file get downloaded to?

  - by Calvin Cheng

  What actually happens to the .box file (which according to the docs is simply a vbox image in tar form, in a particular format) after the first command vagrant box add lucid32 http://files.vagrantup.com/lucid32.box is executed? I can't seem to find the filesystem location of lucid32.box after the download has successfully completed... I am aware it doesn't really matter as vagrant init lucid32 vagrant up vagrant ssh will get me into the vm irregardless. But I am curious where .box is located.

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• How to make write operation idempotent?

  - by Morgan Cheng

  I'm reading article about recently release Gizzard sharding framework by twitter(http://engineering.twitter.com/2010/04/introducing-gizzard-framework-for.html). It mentions that all write operations must be idempotent to make sure high reliability. According to wikipedia, "Idempotent operations are operations that can be applied multiple times without changing the result." But, IMHO, in Gazzard case, idempotent write operation should be operations that sequence doesn't matter. Now, my question is: How to make write operation idempotent? The only thing I can image is to have a version number attached to each write. For example, in blog system. Each blog must have a $blog_id and $content. In application level, we always write a blog content like this write($blog_id, $content, $version). The $version is determined to be unique in application level. So, if application first try to set one blog to "Hello world" and second want it to be "Goodbye", the write is idempotent. We have such two write operations: write($blog_id, "Hello world", 1); write($blog_id, "Goodbye", 2); These two operations are supposed to changed two different records in DB. So, no matter how many times and what sequence these two operations executed, the results are same. This is just my understanding. Please correct me if I'm wrong.

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• Use Margin Auto and Center to center Float Left Div

  - by Yan Cheng CHEOK

  I know this question had been asked many times. http://stackoverflow.com/questions/1740587/float-a-div-to-center However, I follow their suggestion : <center> <div style="margin : auto"> <a href="#" style="float: left; margin-right: 10px;">Menu Item 1</a> <a href="#" style="float: left; margin-right: 10px;">Menu Item 2</a> <a href="#" style="float: left; margin-right: 10px;">Menu Item 3</a> </div> </center> By using "Center" and "Margin Auto", I still unable to center the menu item.

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• How to Implement Dynamic Timestamp in Web Page?

  - by Morgan Cheng

  In Facebook and twitter, we can see that there is a timestamp like "23 seconds ago" or "1 hour ago" for each event & tweet. If we leave the page for some time, the timestamp changes accordingly. Since it is possible that user machine doesn't have same system time as server machine, how to make the dynamic timestamp accurate? My idea is: It is always based on server time. When request is sent to server for the web page, timestamp T1 (seconds to 1970/1/1) is rendered into inline javascript variable. The displayed timestamp ("23 seconds ago") is calculated by T1 instead of local time. I'm not sure whether this is how Facebook/Twitter do it. Is there any better idea?

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• Various way to stop a thread - which is the correct way

  - by Yan Cheng CHEOK

  I had came across different suggestion of stopping a thread. May I know, which is the correct way? Or it depends? Using Thread Variable http://download.oracle.com/javase/1.4.2/docs/guide/misc/threadPrimitiveDeprecation.html private volatile Thread blinker; public void stop() { blinker = null; } public void run() { Thread thisThread = Thread.currentThread(); while (blinker == thisThread) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } } Using boolean flag private volatile boolean flag; public void stop() { flag = false; } public void run() { while (flag) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } } Using Thread Variable together with interrupt private volatile Thread blinker; public void stop() { blinker.interrupt(); blinker = null; } public void run() { Thread thisThread = Thread.currentThread(); while (!thisThread.isInterrupted() && blinker == thisThread) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } }

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• Transferring binary file from web server to client

  - by Yan Cheng CHEOK

  Usually, when I want to transfer a web server text file to client, here is what I did import cgi print "Content-Type: text/plain" print "Content-Disposition: attachment; filename=TEST.txt" print filename = "C:\\TEST.TXT" f = open(filename, 'r') for line in f: print line Works very fine for ANSI file. However, say, I have a binary file a.exe (This file is in web server secret path, and user shall not have direct access to that directory path). I wish to use the similar method to transfer. How I can do so? What content-type I should use? Using print seems to have corrupted content received at client side. What is the correct method?

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• Usage of std::string.append causes "Stack around the variable 'result' was corrupted"

  - by Yan Cheng CHEOK

  I have the following code : std::string Utils::get() { std::string result; result.append(1, 'x'); result.append(1, 'x'); result.append(1, 'x'); return result; } I expect 'xxx' to be returned. However, when I run under debug mode, I get the warning "Stack around the variable 'result' was corrupted" Am I using append function the wrong way?

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• Problem with running Ruby with Cron

  - by Cheng

  My ruby file is like this. `mkdir #{HOST} -p` It works fine by: ruby mycode.rb But in a cron job 0 * * * * ruby ~/backup.rb backup.log It will a -p folder. Why?

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• Should I use threeten instead of joda-time

  - by Yan Cheng CHEOK

  Hello all, I came across http://www.jroller.com/scolebourne/entry/why_jsr_310_isn_t. 1) I am currently migrating Java Calendar to joda-time. I was wondering, should I use threeten instead of joda-time? Is threeten production ready? 2) Can threeten library and joda-time libraries exist together in a same application? As I am using some 3rd parties libraries, which is using joda-time library too. 3) Will joda-time become an abandon project since there is threeten? Thanks.

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• Difference among STLPort and SGI STL

  - by Yan Cheng CHEOK

  Recently, I was buzzed by the following problem STL std::string class causes crashes and memory corruption on multi-processor machines while using VC6. I plan to use an alternative STL libraries instead of the one provided by VC6. I came across 2 libraries : STLPort and SGI STL I was wondering what is the difference between the 2. Which one I should use? Which one able to guarantee thread safety? Thanks.

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• Java Font Display Problem

  - by Yan Cheng CHEOK

  I realize that, in my certain customer side, when I use the font provided by Graphics2D itself, and decrease the size by 1, it cannot display properly. private void drawInformationBox(Graphics2D g2, JXLayer<? extends V> layer) { if (MainFrame.getInstance().getJStockOptions().getYellowInformationBoxOption() == JStockOptions.YellowInformationBoxOption.Hide) { return; } final Font oldFont = g2.getFont(); final Font paramFont = new Font(oldFont.getFontName(), oldFont.getStyle(), oldFont.getSize()); final FontMetrics paramFontMetrics = g2.getFontMetrics(paramFont); final Font valueFont = new Font(oldFont.getFontName(), oldFont.getStyle() | Font.BOLD, oldFont.getSize() + 1); final FontMetrics valueFontMetrics = g2.getFontMetrics(valueFont); /* * This date font cannot be displayed properly. Why? */ final Font dateFont = new Font(oldFont.getFontName(), oldFont.getStyle(), oldFont.getSize() - 1); final FontMetrics dateFontMetrics = g2.getFontMetrics(dateFont); Rest of the font is OK. Here is the screen shoot (See the yellow box. There are 3 type of different font within the yellow box) :

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• Why Windows Live Spaces Fetch Image Through HTTPS?

  - by Morgan Cheng

  I happens to find that, when a live space page is loaded, inline images are fetched by https protocol instead of http protocol. This doesn't make sense. The text part of live space is not fetched by https, why images are fetched with https? I bet the https way to fetch image just make the page loaded slower. Is there any special advantage to choose https over http in this case?

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