Combining Flex and Scala using Liftweb and BlazeDS

I wanted to setup a sample project that uses Flex and Scala. I followed the excellent tutorial on FlexOnRails: Integrating Flex, BlazeDS, and Scala/Lift. The tutorial helps a lot explaining how to set up your sample project. Unfortunately the tutorial is a bit outdated with regard to latest versions. Fortunately I could solve all problems! I’ll list the problems I had. Also, I’ll post my project. I won’t redo the tutorial, as I certainly couldn’t to a better job then Derek Wischusen.

  • First problem I had, was getting my backend compiled. The liftweb has changed slightly, as a result the class Boot.scala didn’t work anymore. I could solve it by downloading the latest Liftweb framework, version 0.9. I copied & pasted the Boot.scala from the sites/examples dir. After a few tweaks (removing code I didn’t need), the project compiled successfully!
  • Then I wanted to setup the flex project. That was quite easy, using the latest version of Flexbuilder (version
    I setup flexbuilder to deploy in the backend/webapp directly, as is explained in the tutorial.
  • I ran the project by running the following maven commands in the backend subdir:
    mvn package
    mvn jetty:run
  • While running the example, I got a AbstractMethodError. I wasn’t the first person to get that error, as I found on the Liftmailinglist. I could fix the problem by using Scala version 2.7.1 for my own project. All in all, when using bleeding-edge technologies, having the latest version isn’t good always!
  • After that I ran the project  again. Now I get a NullPointerException, seems the line val msgBroker = MessageBroker.getMessageBroker(null) returns Null.
    Turned out I forgot to update the web.xml, the Flex servlet and other configuration has to be added.

I named the sample project Elegante. Download the source here: For explanation see the original tutorial.

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