Hello, i start with the programming of a JSF Website. At the moment all files have the .xhtml ending. When i go to http://localhost:8080/myProject/start.jsf everything is all right. But when i rename the file from start.xhtml to start.jsf i became a NoClassDefFound Error.

What is my mistake?

  <servlet-name>Faces Servlet</servlet-name>
    <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Faces Servlet</servlet-name>
    <url-pattern>*.jsf</url-pattern>
  </servlet-mapping>
  <context-param>
    <param-name>javax.faces.PROJECT_STAGE</param-name>
    <param-value>Development</param-value>
  </context-param>