During the JSF lifecycle each input value can be validated. As such the JSF runtime allows you to write validators that will take care of that during request processing.
Several standard validators are part of the standard JSF runtime. Note that the specification has been written with extension in mind so it is also possible to write your own validator and hook it up for request processing.
The next blog entry in the series will describe the actual Java API that will allow you to validate input values. See you then!
Posted September 1, 2012