JSF and Struts overlap in the user interface and form processing arenas, but JSF adds a lot of extra functionality over and above what Struts provides in the user interface arena. This means that JSF isn't replacing Struts anytime soon, and the two make a very powerful combination. As a matter of fact, the lead author of Struts, Craig McClanahan (who is also one of the spec leads for JSF), has written a library to help you use the two together. He's also said a lot about the subject of integration. The two make quite a powerful combination.