Hey, my blog is useful!

My post on getting Apache HttpClient working with Google App Engine is referenced from one of Google's official FAQ pages (the "Will It Play with Google App Engine" page)! I feel special.

Passing JVM arguments for junit with maven

Every time I need to do this, google leads me to this help page, which leads me to the following command, which does NOT work (at least not on my version of Maven):

mvn -Dmaven.junit.jvmargs=-verbose test

The proper help page is for the surefire plugin. So the proper way to do it is:

mvn -DargLine=-verbose test

Parallel Computing benchmarks

I've been doing some benchmarking and hope to post some results soon. I have some simple, easily-parallelized code that I've been trying different computing architectures on. These include:

• Single threaded java
• Single threaded C
• Multithreaded java
• Multithreaded C
• Vectorized C using x64 SSE Instructions
• Multi-core computing on an NVIDIA GPU with CUDA

It's been an interesting experiment and hopefully I can post results soon.

Installing Java Plugin for Firefox on ubuntu

After reading a bunch of confusing articles describing how to install the java plugin into Firebox on Ubuntu Linux 9.04, I found that there is already a package for it:

sudo apt-get install sun-java6-plugin

GWT and Spring / Acegi Security

Using Spring Security with GWT is fairly easy . . . just protect your GWT page and its associated servlets.

But one tricky thing is handling expired logins. When your user's login expires, they may be in the middle of using your web application. They will probably click some widget that will generate a call to the server. Because the login has expired, Spring Security will return your login page instead the expected server response. So you need to set up your GWT client code to handle this.

I got some good tips on how to do this on this page, but to make the ideas contained there a little more concrete, let me give some example code.

In my case, I wrapped the DisplayCallback class from the GWT Presenter library, but you should be able to apply these ideas to any gwt AsyncCallback.

/**
 * This is a special version of DisplayCallback that will handle Spring/Acegi
 * security errors.  If a 403 Access Denied errors occurs, the user will be
 * shown an error message.  If the server returns a Login page, that means the
 * user's login has presumably expired, so we direct the browser to redirect
 * to our login page.
 * 
 * Credit for these ideas comes from here:  
 * http://www.dotnetguru2.org/bmarchesson/index.php/2007/04/23/technical_tip_using_acegi_with_gwt
 * 
 */
public abstract class MyDisplayCallback<T> extends DisplayCallback<T> {

 private static final String SERVER_ERROR = "An error occurred while "
  + "attempting to contact the server. Please check your network "
  + "connection and try again.";

 public StatProjDisplayCallback(Display display) {
  super(display);
 }
 
 @Override
 protected final void handleFailure(Throwable cause) {
  
  doCleanup();
  
  String errorMessage = cause.toString();
  if (errorMessage.indexOf("403") != -1)
  {
   // Access denied for this role
   Log.debug("login invalid for this resource");
   if (GWT.isClient()) {
    Window.alert("Access denied");
   }
  }
  else if (errorMessage.indexOf("Login") != -1)
  {
   Log.debug("login expired, showing login dialog");
   if (GWT.isClient()) {
    Window.Location.assign("login.jsp?relogin=true");
   }
  }
  else
  { 
   Log.error("Handle Failure:", cause);

   Window.alert(SERVER_ERROR);
  }
  
 }
 
 /**
  * This method can be overriden to include code that should run in case the server call fails.  
  * This method will be called by handleFailure()
  */
 protected void doCleanup() {};

 @Override
 protected abstract void handleSuccess(T value);

}

favicon.ico and spring/acegi security

Don't forget to whitelist favicon.ico in your security.xml file. Otherwise, when visiting your site, you may be asked to log in, and then you will just be shown a web page consisting only of your little favicon.ico image, which looks pretty weird.

BitBucket

I use bitbucket.org to store my mercurial projects. It works fine for simple pulls/pushes and it has a nice web interface. My one complaint is that sometimes it is very slow. This is not a big deal for pull/push since I don't do that a whole lot. But I've also been using bitbucket's issue tracking features and sometimes that is unusable (it can take over 2 minutes to bring up an issue report).