JSF and Libraries Unclarity

After some time spent with servlets and JSPs now i'm trying to learn something about JSF. I've learned the basics, made a couple of simple examples, have a basic ideea of the 'workflow' but I still can't understand what's with the javax.faces.webapp.FacesServlet thing.

<servlet>
  <servlet-name>Faces Servlet</servlet-name>
  <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
  <load-on-startup>1</load-on-startup>
  </servlet>
<servlet-mapping>
  <servlet-name>Faces Servlet</servlet-name>
  <url-pattern>*.jsf</url-pattern>
  </servlet-mapping>

I know that "Faces Servlet" it's just an 'internal' name just for the XML and that it gets bind with a class, in this case: javax.faces.webapp.FacesServlet. But where is this class anyway?! I'm using Eclipse, created a new Dynamic Project, GlassFish 4.0 as Server, JSF 2.0 as Configuration (selected no library) and neither did I import any jar. How can it be working? And when I try to run the same thing with JBoss I must import a javax.faces-2.2.2.jar file.

Ok, the library might be already included in GlassFish since it works but... will I face any problems if I try to deploy my app on another server? Like JBoss or Websphere.

In a nutshell: what are the prerequisites when working with JSF technology :)

Thank you.

javax.faces.webapp.FacesServlet is a class that implements Servlet interface. In order to be recognized in your application, you should add it in the web.xml as a <servlet>. This is basically done in this configuration:

<servlet>
    <servlet-name>Faces Servlet</servlet-name>
    <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

Now, we can refer to this class in the web.xml file using the Faces Servlet name. Next thing do to is define the URL that will be handled by this servlet. This is done in this configuration:

<servlet-mapping>
    <servlet-name>Faces Servlet</servlet-name>
    <url-pattern>*.jsf</url-pattern>
</servlet-mapping>

So, any GET or POST request to this application server that ends with jsf suffix will be handled by Faces Servlet. You can use other URL patterns for the servlet mapping. This is better explained here: JSF Facelets: Sometimes I see the URL is .jsf and sometimes .xhtml. Why?

will I face any problems if I try to deploy my app on another server? Like JBoss or Websphere?

If the application server is a Java EE 5 compliant server, then you will have access to this servlet by using Mojarra implementation in form of JSF 1.2. For Java EE 6 compliant servers this will be in Mojarra implementation in for of JSF 2.x (check the notes of the application server to know the exact version). Currently, with GlassFish 4, you get Mojarra for JSF 2.2.

In case the application server is not a Java EE compliant server e.g. Tomcat, you must add the libraries manually in WEB-INF/lib folder of your web application. Which libraries to add? Depending on the JSF version and its requirements (read further).

what are the prerequisites when working with JSF technology?

This is covered in StackOverflow JSF wiki. Taken from there:

Minimum requirements

JSF 1.0 and 1.1 requires a minimum of Servlet 2.4 / JSP 2.0 and Java 1.4.

JSF 1.2 works on Servlet 2.4, but requires a minimum of JSP/EL 2.1 which goes hand in hand with Servlet 2.5, so it after all requires Servlet 2.5. If you replace JSP 2.1 by Facelets 1.x as default view technology, then you can use JSF 1.2 on Servlet 2.4. It requires a minimum of Java 1.5.

JSF 2.0 which uses by default Facelets 2.x requires a minimum of EL 2.1 which goes hand in hand with Servlet 2.5, so it requires after all Servlet 2.5. If you supply your own EL 2.1 API/impl, then you can in theory run JSF 2.0 on Servlet 2.4. It requires a minimum of Java 1.5.

JSF 2.1 uses some Servlet 3.0 specific features, but is backwards compatible with Servlet 2.5. Those Servlet 3.0 features are optional.

JSF 2.2 requires a minimum of Servlet 3.0, because of the new file upload component which is internally using the standard Servlet 3.0 API without the need for 3rd party libraries. It requires a minimum of Java 1.6.

Examples of Servlet 2.4 containers are Tomcat 5.5.x, JBoss AS 4.x and Sun Java Application Server.

Examples of Servlet 2.5 containers are Tomcat 6.0.x, JBoss AS 5.x and GlassFish 2.x.

Examples of Servlet 3.0 containers are Tomcat 7.0.x, JBoss AS 6.x and 7.x and GlassFish 3.x.

Examples of Servlet 3.1 containers are Tomcat 8.0.x, WildFly 8.x, and GlassFish 4.x.