Facelets

One notable difference between modern versions of JSF and earlier versions is that Facelets is now the preferred view technology. Earlier versions of JSF used Java Server Pages (JSP) as their default view technology. Since the JSP technology predates JSF, sometimes using JSP with JSF felt unnatural or created problems. For example, the JSP lifecycle is different from the JSF lifecycle; this mismatch introduced some problems for JSF 1.x application developers.

JSF was designed from the beginning to support multiple view technologies. To take advantage of this capability, Jacob Hookom wrote a view technology specifically for JSF. He named his view technology Facelets. Facelets was so successful it became a de-facto standard for JSF. The JSF expert group recognized Facelets' popularity and made it the official view technology for JSF in version 2.0 of the JSF specification.