Thursday, 24 April 2014

PrimeFaces, JSF 2.2 and CDI on Google App Engine


Recently we did a proof of concept on Google App Engine, the cloud solution of Google. The Java version, supports servlets and you can already find various resources on the internet where the procedure is described to have the technologies listed in the title working on the platform.

But some of them are already quit old or give only a partial solution.  So I decided to put our findings together in this blog post.  All the frameworks are from the Apache group or have the Apache License.

We used version 1.9.1 of the Java GAE SDK.


The most difficult technology of the list is JSF. You can find various posts where you have to create your custom version of Mojarra to be able to deploy it.  This has to do with the use of JNDI sources which is not allowed on AppEngine.

We tried the Apache MyFaces 2.2.2 version and it went remarkable smooth.  We made the following  configuration options in the appengine-web.xml file.

        <exclude path="/**.xhtml" /> 

The least obvious things was that we needed to tell AppEngine that xhtml files aren’t static, so that we can define it as an url pattern for the faces servlet.  Using this url extension is a best practice so that you can’t retrieve the raw html files of JSF.

EL 2.2

At this point, we were already able to deploy a JSF application and had the hello world style application working.  But if we tested with method expressions, like

<h:commandButton value="Greet" actionListener="#{testAction.doGreeting()}" />

We received an error that the brackets weren’t expected.  So it was clear that only value expressions are recognised and not the method expressions.

We tried various EL expression factories, and it turned out that the one of JBoss worked best.  But we weren’t able to use the latest version of the framework. we received following security exception

access denied ("java.lang.RuntimePermission" "modifyThreadGroup")

Although it is a CR release, it did the job so we stayed with this maven artefact  org.jboss.el:jboss-el:1.0_02.CR6


Plain JSF applications aren’t attractive, that is why you use some component library like PrimeFaces which became the de facto standard.  Adding this to artefact to the maven dependencies, we hit another issue, but this time we identified it as a known GAE bug.

It has to do with the handling of the If-Modified-Since request header.  But we quickly found an excellent solution by Derek Berube.

Adding the 2 classes and define the filter in the web.xml file, the problem was solved.

We even tried the latest PrimeFaces 5.0 version (it was just before it went into his first CR release) and there was no other issue we could see at first glance.  So this means you can now create web application targeted to mobile devices on Google App Engine.


As I’m a strong believer of Java EE, so I tried to use CDI for the middleware instead of the Spring approach too many people take without considering the alternatives.

There is an excellent Apache implementation of CDI, called OpenWebBeans.  The following artefacts where added to the project

  • openwebbeans-impl
  • openwebbeans-spi
  • openwebbeans-web
  • openwebbeans-jsf
  • openwebbeans-el22

Regarding the configuration of OpenWebBeans, we just had to follow the procedure for a regular web server like Tomcat or Jetty.
After adding an empty beans.xml file and define the WebBeansConfigurationListener in the web.xml, the dependency injection worked like a charm.

Just as with JSF, there exists also for CDI an extension beyond the basic stuf and I choose CODI (Apache MyFaces Extensions CDI). Just adding the dependency was enough to make it work.

Other technologies

We also added the JPA option and used a maven plugin to handle the deploy to Google App Engine automatically when a mvn deploy command is issued.

I find it a pity that there is no database solution available for free on Google App Engine. It doesn’t need to be very powerful. Just a simple schema that you can use for demonstration purposes of your application.

This is in contrast with the JBoss OpenShift offering, where you can have a full Java EE stack with a database for free.  But that will be covered in another blog post.


Apart from one little issue (bug 8415) which can easily be bypassed, it was quit easy to assemble the required stack to have a JSF based web development environment on Google App Engine. This is in contrast with a few years back where various issues limited the possibilities.