If a user attempts to submit a form with one or more required fields missing, an error
message is automatically generated.
The error message is generated by the <h:message> tag corresponding to the
invalid field. The string First Name in the error message corresponds to the value
of the label attribute for the field. Had we omitted the label attribute, the value
of the field's id attribute would have been shown instead. As we can see, the
required attribute makes it very easy to implement mandatory field functionality
in our application.
Recall that the age field is bound to a property of type Integer in our named bean.
If a user enters a value that is not a valid integer into this field, a validation error is