OVal - Validate Your Models Quickly and Effortlessly!
Some time ago one of the projects at work required me to validate
some Java POJOs. Theses were my model classes and I’ve been creating
them from incoming WebService requests. One would say that XSD would be
sufficient for the task, for parts of this validations - sure, it would.
But there were some advanced rules XSD would not handle, or would render
the schema document very complicated.
Rules I needed to express were like:
person’s first_name and last_name should be of appropriate length -
between 2 and 20, and additionally one could pass a zero-length string
just to remove the previous value
state field should consist only defined values - as in
dictionary value - this one would be completable with XSD’s
enumerations, but would require often changing schema files and
redistributing them to interested parties :(
The library I’ve decided to use for this task is OVal and it came out really nice! Read on
to find out the details!
Oval is quite mature library that allows POJO validation, but is not
JSR303 (bean validation) implementation. It has converters that enable
it to understand those annotations, but I’m not sure about the
I’ve tried only a subset of the available checks, among which
There are many more, and their attributes give interesting ways to
configure the validation process. But using them was rather easy and did
not require to much brainstorming. What I really needed were custom
checks. And in this area OVal shows it’s strength. Implementing a check
is really easy.
I needed an annotation that would check a field against some values in
a dictionary. If field’s value was in the given set, than the validation
would succeed, if not, an exception would be thrown. To accomplish this
task it is required to implement two classes: annotation class and check
class - called by the validation engine on a given field.
Let’s start with our new annotation:
In the above snippet I’ve defined a check-annotation, that would be used like
You can pass file - containing dictionary values for this field.
There is also message field in the annotation which is an error
message returned by the validation engine of failed check - pretty
handy. And can be expressed in .properties file as:
Placeholder, like context, will be replaced with correct values supplied by the
Annotating a field is not enough. It is also needed to create a validator
for this kind of check. The name of the class is already defined in
DictionaryValue annotation, it is called
DictionaryValueCheck and I’ve done this check this way:
What this basically does is:
when file is set - read dictionary content from the file into
upon check request just lookup value in dictionary parsed from the
And that’s it!
For me Oval is really great tool. With it at ones disposal it is extremely easy to create any
imaginable validation you need. This library is really easy to use and
offers lots of handy features.
But perhaps I’m reinventing the wheel and all this can be done easily
with some other library? Share Your opinion!