Posts tagged jsf2

Last night I wanted to play around with the Google App Engine. Google’s cloud service should ring a bell? Don’t worry if it doesn’t, you can read more about it and use this tutorial as your first GAE-project!

Due to my interest in JEE6-technologies, I was interested whether the latest Google App Engine (1.4.3) supported the latest technologies in Java: JSF2 for the view layer, and CDI ( Contexts and Dependency Injection for the Java EE Platform ) to wire everything up.

In this article I will briefly discuss what problems I have encountered while setting up this environment.

Shortcut: If you’re only interested in the result, and want to get started right away, you can download the full eclipse project here. No GAE or CDI dependencies!

Project Setup

JSF2 on the Google App Engine

To get started, I advise you to follow the guide ‘Configuring JavaServer Faces 2.0 to run on the Google App Engine Using Eclipse‘ described on the Google website. It is pretty much complete, well documented with screenshots, and a breeze to follow.

The guide will set up your IDE, configure the Google App Engine plugin, download and configure the required libraries for setting up JSF2 on the Google App Engine.

Adding CDI

Download Weld 1.1.1-FINAL. Extract the download, it contains the following libraries which you need to add to the build path:

1. cdi-api.jar
2. weld-api.jar
3. weld-core.jar
4. weld-servlet.jar

Add the following listener to your web.xml :

<listener>
    <listener-class>org.jboss.weld.environment.servlet.Listener</listener-class>
</listener>

To finalize the configuration of CDI in your GAE-application, add an empty beans.xml file to your WEB-INF folder. This is needed by default by CDI to enable classpath scanning.

Problems encountered

Startup fails – InitialContext

After following the Google tutorial on setting up JSF2 on GAE, you’ll notice something odd. Yes, your application isn’t starting up!
This is the stracktrace:

WARNING: Error starting handlers
java.lang.NoClassDefFoundError: javax.naming.InitialContext is a restricted class. Please see the Google  App Engine developer's guide for more details.
	at com.google.appengine.tools.development.agent.runtime.Runtime.reject(Runtime.java:51)
	at com.sun.faces.config.WebConfiguration.processJndiEntries(WebConfiguration.java:578)

As you can see, the com.sun.faces.config.WebConfiguration class tries to load up an InitialContext in the processJndiEntries method. The InitialContext class is not allowed by the Google App Engine for obvious reasons.

When we take a look into the WebConfiguration.java class ( love open-source! ), we can clearly see the InitialContext being loaded:

private boolean canProcessJndiEntries() {

        try {
            Util.getCurrentLoader(this).loadClass("javax.naming.InitialContext");
        } catch (Exception e) {
            if (LOGGER.isLoggable(Level.FINE)) {
                LOGGER.fine(
                      "javax.naming is unavailable.  JNDI entries related to Mojarra configuration will not be processed.");
            }
            return false;
        }
        return true;

    }

The App Engine is freaking out and throws the restricted class exception. Thanks to open-source we can clearly see what’s going on, and modify it to our own needs. Since we don’t need any JNDI-lookups, we can safely remove this method.

Copy paste the original java sourcefile to the same package in your project (com/sun/faces/config/), and comment out all references to the InitialContext.

You can download the result, for version jsf-impl-2.0.2-FCS.jar, here.

Enable Sessions

Sessions are disabled by GAE by default. The following exception is thrown.

java.lang.RuntimeException: Session support is not enabled in appengine-web.xml.  To enable sessions, put true in that file.  Without it, getSession() is allowed, but manipulation of sessionattributes is not.
	at com.google.apphosting.utils.jetty.StubSessionManager$StubSession.throwException(StubSessionManager.java:77)
	at com.google.apphosting.utils.jetty.StubSessionManager$StubSession.setAttribute(StubSessionManager.java:65)

The exception is well documented; as mentioned, you need to put true in the appengine-web.xml file.

JSF configuration

1. GAE supports server state saving, so use the javax.faces.STATE_SAVING_METHOD param
2. Projectstage can be any one of the phases
3. The expressionfactory needs to be explicitly set due to a GAE-bug
4. We enable the xml validation checks
5. Spawning threads is disallowed in GAE. By setting the com.sun.faces.enableThreading param to false, JSF will not spawn childthreads

<context-param>
    <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
    <param-value>server</param-value>
</context-param>
<context-param>
    <param-name>javax.faces.PROJECT_STAGE</param-name>
    <param-value>Development</param-value>
</context-param>
<context-param>
    <param-name>com.sun.faces.expressionFactory</param-name>
    <param-value>com.sun.el.ExpressionFactoryImpl</param-value>
</context-param>
<context-param>
    <param-name>com.sun.faces.validateXml</param-name>
    <param-value>true</param-value>
</context-param>
<context-param>
    <param-name>com.sun.faces.enableThreading</param-name>
    <param-value>false</param-value>
</context-param>

References

• Google Guide to configuring JSF 2.0 to run on the Google App Engine. I used this guide myself to get started, but some errors I encountered aren’t discussed in it. (link)
  
• Article discussing the solution to the ‘javax.naming.InitialContext is a restricted class’ problem. (link)
  
• JavaServer Faces 2.0 and Google App Engine Compatibility Issues (link)