The Client Side Validation API makes it possible to write our own validators and converters. The writing process is straightforward.

In this recipe, we will develop a custom JSF validator that validates any Unicode strings. The validator will check whether an input value consists of letters, spaces, hyphens, and apostrophes. Any other characters are not allowed. This is a common requirement for validating names of persons, addresses, and similar inputs. We will use the CSV API to implement both server-side and client-side validators. After that, we will see validation in action.