JavaFX Form Validation
jonathan.giles at oracle.com
Sun Jun 10 16:52:10 PDT 2012
I'm currently in the very, very early stages of developing a validation
API for future inclusion into JavaFX. I thought rather than get too far
into the research and development of a proof of concept, I would see
what you all think. Any feedback now would be very useful.
Essentially, there are a few common styles related to form validation.
Some of the more likely approaches include:
* The 'JGoodies Validation framework'  approach, where the
developer provides a Validator that will then run over the form and
gather feedback to return to the user (for example, it would test
that the 'name field' is not empty, and that the email address is of
the correct style - if either of these rules are invalid, the
Validator would return ValidationMessage instances inside a
ValidationResult). If validation fails the user is shown the text
out of the ValidationMessage feedback, otherwise the form would
submit as per usual. This validation may happen at a number of times
(during form submission, when focus is lost, as a key is typed,
etc). The nice thing about this approach is that the Validator can
be a part of the domain model, the presentation model, or a separate
* The JSR-303 approach which uses annotations to indicate the rules
applicable to each field. These annotations are on the domain model,
and therefore assumes that the form is directly tied to a domain
object (which may not always be correct). I think the JSR-303 API is
too complex for what is needed in JavaFX, but a similar
implementation could be developed with a simpler API that follows
* For lack of a better reference point, the FXForm approach  which
encapsulates the validation inside a Form object that can be placed
in the scene. I know this isn't explicitly (in the case of FXForm)
about validation, but I think it is another approach to consider.
So, what does JavaFX need out of a validation framework? It's really
five things (I think):
1. A way for developers to validate a form by providing some means of
specifying rules, as well as a way to specify when it runs, how it
is visually represented, etc.
2. A way for the validation to impact upon the visual state of the form
(using consistent CSS pseudoclass states / style classes, as well as
by showing custom overlays, error messages beside the component (or
grouped together at the top of the form)). There must be API to
specify all of this.
3. Convenient API to simplify the validation process  (e.g.
isEmpty(String), isAlphanumeric(String), etc, etc, etc).
4. An API that does not require it be integrated with UI controls.
Doing so would prevent 3rd party UI controls to be able to be
validated without also implementing the API, which may prove
burdensome. Instead, the validation API should be separate.
5. A means to integrate nicely with the bindings and properties API
present in JavaFX today.
Of the three approaches above, my personal preference is to follow the
JGoodies approach as I think it is the most powerful and flexible.
However, nothing is set in stone and I want to learn what others think.
Note that at present this research does not extend to considering
whether there should be API related to automatically generating a form
from a (JavaFX) bean (and making use of the validation API to ensure the
input is correct). However, I am not against discussing this topic as
well, as long as it too integrates nicely with the rules above, as well
as the validation API itself, obviously. This research may full into
requirement three above.
More information about the openjfx-dev