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).

Building OpenCV 2.0 with Visual Studio C++ 2008 Express Edition

Hopefully I will spiff this post up with some screenshots, but for now, let me just quickly note the steps that were required to get this to build.

1. Download and install VS C++ Express Edition
2. Download and install CMake. When the install asks, don't bother having it put on your System Path.
3. Download and install OpenCV 2.0. There is a Windows installer. Note: This does not install a working open cv library . . . it is just the source files. Again, don't bother having the installer put OpenCV on your system path.
4. Run the CMake GUI in your CMake installation. For the source directory, indicate the OpenCV directory (probably C:\OpenCV2.0). For the build directory, specify a build directory that you've created (recommended: C:\OpenCV2.0\release).
5. Click the Configure button.
6. In the configuration options, disable OpenMP. You probably won't have this if you are using VS C++ Express Edition.
7. Click the Configure button again. Then click Generate.
8. Go to your build directory (C:\OpenCV2.0\release). Open the Visual Studio Solution file. Once you're in Visual Studio, build the project (f7). This will take a while.
9. You're done. When you create new projects, use the Lib and Include files in your build directory. (You'll need to add these to your Project properties). I'll try to explain more later and maybe include a sample test project.

Working with GWT / Spring / Dispatch

The Hive Development blog has a nice tutorial on setting up a Google Web Toolkit app with the Presenter and Dispatcher patterns. This is all based on a nice Google presentation explaining some useful patterns for developing robust app with GWT.

I recommend watching the video first and then reading the hivedevelopment blog article. Read through it and then download the full source code using the link near the top of the page. In the end, it's helpful example starter application for exploring concepts.

Anyways, the framework that you end up with uses Google Guice for server-side dependency injection and the servlet config. I am going to describe how I converted that to use Spring instead, using the GWT-Dispatch-Spring library. Comments are welcome since I am probably not doing things optimally in some places.

Why would you want to do this? I think it is personal preference whether you use Guice or Spring (nice discussion/war going on here). I am fairly new to both so I don't have a personal opinion. In the end of this, you will end up with a project using Guice's ally Gin on the client and Spring on the server, so you can be like Switzerland and remain neutral. ;)

The major steps described here include:

• Adding the Spring and gwt-dispatch-spring-ext jars to your project
• Eliminating Guice from your server code
• Adding the Spring configuration to your server code
• Switch the client to use the Spring version of the DispatchAsync

Initial Setup

As I mention above, I recommend going through the blog and then downloading the tutorial code. Import the code into Eclipse (File->Import->Existing Projects Into Workspace). Make sure it all builds and that you can run it in the debugger.

Add Jars

Download the Spring library jars.
Download the gwtrpc-spring library.
Download the GWT-Dispatch-Spring extension library.
Import these jars into the project's war/WEB-INF/lib directory (right-click on the directory, Import->File System):

• spring-aop-2.0.8.jar
• spring-beans-2.5.6.jar *
• spring-context-2.5.6.jar *
• spring-core-2.5.6.jar
• spring-security-core-2.0.4.jar
• spring-web-2.5.6.jar
• gwtrpc-spring-1.01.jar *
• gwt-dispatch-spring-ext-1.0.0 *

The jars that I've marked with an asterisk also need to be added to your build path (Right click Referenced Libraries in the package explorer, Build Path->Configure Build Path).

Eliminate Guice from Server Code

Just delete the entire greet.server.guice package.

Configure the Server Code Using Spring

Modify SendGreetingHandler

There are several things we need to do to adapt the SendGreetingHandler to use Spring:

• All your Handlers will now inherit from SpringActionHandler instead of implementing the ActionHandler interface.
• To inherit from SpringActionHandler, we need a new constructor since that class requires the ActionHandlerRegistry to be passed in.
• We need to swap out the Guice annotations and replace them with their Spring counterparts. We use @Autowired instead of @Inject. We also label the class as a @Component.
• I haven't yet hooked back up the Logging functionality. An exercise for the reader.
• To get the servlet and http request context, we are using the gwt-spring-rpc library RemoteServiceUtil.

Here is what my class looks like after making these changes:

@Component
public class SendGreetingHandler extends SpringActionHandler<SendGreeting, SendGreetingResult> {
 
 @Autowired
 public SendGreetingHandler(ActionHandlerRegistry actionHandlerRegistry) {
  super(actionHandlerRegistry);
 }

 @Override
 public SendGreetingResult execute(final SendGreeting action,
       final ExecutionContext context) throws ActionException {
  final String name = action.getName();
   
  try {

      String serverInfo = RemoteServiceUtil.getThreadLocalContext().getServerInfo();
      String userAgent = RemoteServiceUtil.getThreadLocalRequest().getHeader("User-Agent");

      final String message = "Hello, " + name + "!<br><br>I am running " + serverInfo + ".<br><br>It looks like you are using:<br>" + userAgent;

   
   //final String message = "Hello " + action.getName(); 
   
   return new SendGreetingResult(name, message);
  }
  catch (Exception cause) {
   
   throw new ActionException(cause);
  }
 }

 @Override
 public void rollback(final SendGreeting action,
        final SendGreetingResult result,
        final ExecutionContext context) throws ActionException {
  // Nothing to do here
 }
 
 @Override
 public Class<SendGreeting> getActionType() {
  return SendGreeting.class;
 }
}

Create applicationContext.xml

This file will configure Spring to do annotation-based dependency injection. It also indicates to Spring that it should search the Spring/Dispatch package and our own server code package when looking for components to match dependencies. Place this in war/WEB-INF.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx"
 xmlns:context="http://www.springframework.org/schema/context" xmlns:p="http://www.springframework.org/schema/p"
 xsi:schemaLocation="
  http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
  http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd
  http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">


 <context:annotation-config />
 <context:component-scan base-package="com.adeoservices.gwt.dispatch.spring.server" />
 <context:component-scan base-package="co.uk.hivedevelopment.greet.server" />

</beans>

Change web.xml

We need to change our servlet to use a RemoteServiceDispatcher servlet. Change web.xml to this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app
    PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app>

 <listener>
  <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
 </listener>

 <servlet>
  <servlet-name>dispatcher</servlet-name>
  <servlet-class>org.gwtrpcspring.RemoteServiceDispatcher</servlet-class>
 </servlet>

 <servlet-mapping>
  <servlet-name>dispatcher</servlet-name>
  <url-pattern>*.rpc</url-pattern>
 </servlet-mapping>


 <servlet>
  <servlet-name>remoteLoggerServiceImpl</servlet-name>
  <servlet-class>com.allen_sauer.gwt.log.server.RemoteLoggerServiceImpl</servlet-class>
 </servlet>


 <!-- Default page to serve -->
 <welcome-file-list>
  <welcome-file>GreetMvp.html</welcome-file>
 </welcome-file-list>
 
</web-app>

Quick Review: What We Just Did

At this point, we have converted the Server side code to use Spring instead of Guice. Try running the app. You will probably notice a bunch of logging statements in the Console regarding the Spring dependency injection scanning:

1253 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory  - Creating instance of bean 'sendGreetingHandler'
1254 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory  - Returning cached instance of singleton bean 'springActionHandlerRegistry'
1255 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory  - Autowiring by type from bean name 'sendGreetingHandler' via constructor to bean named 'springActionHandlerRegistry'

Try clicking the button to send the GreetAction to the server. You get an error because we haven't yet adjusted the client to work with Spring and to look for the new Spring RemoteServiceDispatcher that we defined in our new web.xml.

Update Client to Use Spring DispatchAsync

First, we need to add the Dispatch-Spring library to our client code. Add the highlighted line to GreetMvp.gwt.xml:

<inherits name='net.customware.gwt.dispatch.Dispatch' />
<inherits name="com.adeoservices.gwt.dispatch.spring.Dispatch-Spring"/>

Now, we just need to use the Spring-based DispatchAsync. Here is how I did it. I don't like it this way, so maybe somebody can help me (I'll explain). Go to the GreetingPresenter. Modify the constructor so that it takes a SpringDispatchServiceAsync instead of DispatchAsync:

public GreetingPresenter(final Display display, final EventBus eventBus, final SpringDispatchServiceAsyncImpl dispatcher, final GreetingResponsePresenter greetingResponsePresenter) {

What I don't like is how the GreetingPresenter now requires a specific implementation for DispatchAsync. What would be more appropriate is to configure Gin to inject the correct implementation in GreetingClientModule. At this point, I can't figure out how to get this to work: gin complains that DispatchAsync has been "double-bound". But I am basically brand new to Gin/Guice so I'm probably missing something.

In any case, the app should be working and the Client should receive a valid response from the server. You now have a working example using Spring on the server!

Using Apache HttpClient 4 with Google App Engine

The ESXX blog has some handy code for integrating Apache HttpClient 4 with Google App Engine. Since it includes working source code, everything you need to figure it out is there. However, it can be a little confusing at first if you try dropping the code directly into an App Engine project. Your project will fail to compile as it uses several functions that are not supported by the App Engine SDK.

Instead of putting the problematic source code directly in your project, put them in a separate jar file. Then you can include that jar file in your project and everything should work fine.

I did this by creating a simple java project in eclipse, with just the two adapter code files. To get this to build, I also included the apache httpclient jars and the app engine sdk jar. I've included an image of my simple project structure here. Eclipse should automatically build the files once those jars are in place.

Then, at the command line, I simply went to that project's build directory and manually built the jar file using "jar cf GAEHttpClient.jar *". You can of course use your own jar file name. Make sure you build the jar at the root of your build directory structure.

Once your jar file is built, you should be able to add it to your main App Engine project (right click on the project in your Package Explorer and go to Build Path-> Configure Build Path-> Add external JARs . . . then add it to your war/WEB-INF/lib directory using File->Import->General->File System . . .) Once you have that (and the Apache httpclient jars) in place, you should be able to compile your code without error:

HttpParams httpParams = new BasicHttpParams();
ClientConnectionManager connectionManager = new GAEConnectionManager();
HttpClient httpClient = new DefaultHttpClient(connectionManager, httpParams);