Tag Archives: gae

Mixture of technology at Google App Engine (GAE)

Platform

F1Dashboard is build and deployed on Google App Engine (GAE). I started this as an experiment and as a toy project just to learn something new.

GAE is not a new idea, it is another platform for cloud computing. Main difference from others is the Database model. GAE is using a thing called Data Store (Big Table), which is not a normal relational database that anyone used to. There is no schema defined, and querying is impossible without indexing it before. It is something like a massive bag that could store stuff in.

GAE is offered as Python and Java. The later was released long time after Python. It has limited version of JVM environment and a whole bunch of Google services to use. Lots of standard JDK types got repackaged by Google just to limit standard Java functionality, like spawning a Threads.

GAE offers standard Java servlets as web technology. This means that you could use some of the well established frameworks out there. I decided to create one myself of course Something simple and not complicated.

Language

I choose Groovy, just because I wonted to learn another dynamic language and I liked the way Groovy did closures.

Patterns

The framework I did follows MVC pattern. It has single servlet entry. Every requested URL is parsed internally and resolved into Controller and Action. I’m using String Template as rendering engine for my views.

All database operations are entirely hidden behind Repositories, and I made it simple to switch from Objectify to Data Nucleus to anything else that comes.

I choose Objectify for its simplicity. If you are starting with GAE I would very much recommend it.

UI

The design is simple and was done by fried of mine Mike from Rosslyn Digital.

I plugged in jQuery Tools for Overlay effect. It also has a nice plugin for picture gallery.

I also added automatic Twitter updates for every message that is updated on a site.

Updates

Site is automatically harvesting for new content from various of Formula 1 related sites. There is also content from Twitter, YouTube and Flickr. It is utilizing GAE cron jobs for that.

I’m trying to gather some ideas for what I can do with the site in near future. If you have an idea, drop me an email. You can also see latest updates on a site at http://blog.f1dashboard.com

Cheers, Greg

F1 Dashboard released

2 Replies

In last few months I was working on a little personal project. When Google App Engine team announced that preview of Java version is available I decided to give it a try. When I was looking for a subject of my application, one of the ideas started to emerge more that others. I was looking for a web site that could aggregate all the information about Formula 1 racing. Because there was none available (or my Google search ended on first few results that were not satisfactory) I decided to make one.

Few weeks and cups of coffee latter F1Dashboard.com is released.

F1 Dashboard screen shot

Generalities

So, in few words, F1 Dashboard is agregator of news, and media feeds from world of Formula 1. I decided not to collect content, just store information where to find it and short description.

News are harvested from a number of web sites. Twitter updates serves as another source of news.

Images are comming from Flickr, videos from YouTube.

All updates are happening every few minutes and are 100% automated.

Technicalities

GAE supports Groovy as one of JVM programming languages. I decided to give it a try. I love Groovy, it is somewhere in between a friendly and known Java API and Ruby programming language.

It took me a moment to use to BigTable type of DataStore. It restrictes a way I used to work with databases normaly. Google provide entire environment for local development, whitch means I don’t have to upload to a cloud to see working result.

I created a little homegrown Model Views Presenter/Controller framework and used StringTemplate as rendering engine.

jQuery is the library of choice to handle all JavaScript.

Page styling was done by a friendly and kind designer from Circa82 Michael Austin (thanks buddy).

Come on guys, give it a try and tell me what you think Feedback greatlly appriciated. http://www.f1dashboard.com

Cheerios, Greg

Groovy with JDO on Google App Engine, enhancing with DataNucleus

2 Replies

I have some time this days and I’m trying to fly some clouds with Google App Engine (GAE), Now when they have released Java support I can try to use Groovy. Today I tried to implement some simple storage using JDO. GAE team supports some of its features via DataNucleus. DataNucleus is using a post compilation hook to enhance any persistable classes.

Having Groovy in a lib folder of your war (GAE runs your application from this folder) I need to put asm library as well. Latest version of Groovy (1.6.1) has a dependency on asm library in version 2.2.3. On the other hand DataNucleus enhancer has dependency on asm library in version 3.1.

GAE Java SDK is shipped with Ant task for enhancing persistable classes. It also contains Ant macro definition file that makes it simple for usage. Unfortunately this macro includes all libraries from application lib folder. This is causing Enhancer to use asm library in a version that causes it to fail massively.

[enhance] SEVERE: An error occured for ClassEnhancer "ASM" when trying to call the method "org.datanucleus.enhancer.as
m.ASMClassEnhancer" on class "getClassNameForFileName" : org.objectweb.asm.ClassReader.accept(Lorg/objectweb/asm/ClassVi
sitor;I)V

Number of this error messages is as big as the number of classes in my application.

Solution is to exclude asm library from the macro that Google shipped. Easiest way is to edit, or copy to your local application folder and use it there. The line problematic line of code is in classpath element.

<classpath>
          <pathelement path="${appengine.tools.classpath}"/>
          <pathelement path="@{war}/WEB-INF/classes"/>
          <fileset dir="@{war}/WEB-INF/lib" includes="*.jar">
          </fileset>
</classpath>

The easiest way to fix it is to exclude asm library in fileset element, just like this:

<classpath>
          <pathelement path="${appengine.tools.classpath}"/>
          <pathelement path="@{war}/WEB-INF/classes"/>
          <fileset dir="@{war}/WEB-INF/lib" includes="*.jar" excludes="asm*.jar">
          </fileset>
</classpath>

Hope that helps anyone with similar problem.

Cheers, Greg

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