I work on an application that works on multiple application server platforms. As a result, we often find ourselves at odds with the implementation details. A major example is WebSphere which has Apache MyFaces and OpenWebBeans (CDI) which is considerably different from GlassFish with Mojarra and Weld. This has resulted in us having to code around differences in the platforms. This is not sustainable. We decided to set the target JSF layer to use 2.1.x since the application must run easily on EE6/7 containers. We also decided to use Mojarra (JSF RI) as our implementation. So you may be asking how this fits into the title of today's topic. Well the implementations of JSF vary over the containers like GlassFish, Weblogic, JBoss (WildFly), and WebSphere. The mechanism to override the container implementation also varies. I wanted a simple way to validate that the version of JSF (in this case 2.1.26) was overriding the container.
Apache MyFaces has a really easy mechanism for determining the version, but Mojarra does not have something like a "Version" class. I went looking through the Mojarra implementation looking for a way to determine it easily. I then asked Manfred Riem, Oracle, how to determine the version. He sent me a response that I thought was unbelievably simple and I thought I would share it. I have also added it to my library of utilities I have for JSF.
JSF Utilities Library on Bitbucket: jsf-utils
Here is the code for your enjoyment. Simple and sweet...
So I created a simple web page that displays the information, and I can be sure that we have successfully overridden the application server's implementation.
Update: If you are using OmniFaces framework, the Faces class has a method to determine implementation version.