Annotations and bean validation with Groovy

I was looking for something like annotations driven validation for Groovy. Something like JSR-175 but... without JSR-175. Maybe something like Spring Validator would be nice but... without Spring.
Something like this:

class FooBeanWithValidations  {

@NotEmpty
String id

}

I have reviewed some options, but i was looking for somthing very simple and plain...so, finally, i have to write it by myself...
First I defined the annotation class:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface NotEmpty {

}

And then i writed a Validation class which handles the annotations and performs validation logic:

class Validator {

/**
 * Helper method for apply a closure over all annotated bean properties 
 */
protected static def forEachAnnotatedField(def clazz, def annotationClass, def closure) {

 if (clazz in [Object, GroovyObject]) {
  return
 }

 def properties = clazz.declaredFields
 def annotated = []
 annotated.addAll(properties.findAll {field ->  
  def annot = field.annotations.find {annotation->
   return (annotationClass.isAssignableFrom(annotation.class))
  }

  if (annot){
   closure(field, annot, clazz)
  }
 })

 forEachAnnotatedField(clazz.superclass, annotationClass, closure) 
}


/**
 * Perform NonEmpty validations
 */
static def validateNotEmpty(def bean) {

 forEachAnnotatedField (bean.class, NotEmpty.class) {field, annotation, clazz ->
  def value = bean."${field.name}"
 
  //Be aware with boolean values. False value are not empties!!
  if (value instanceof Boolean) {
   return
  }
 
  if (!value){
   throw new ValidationException(bean, field.name, null)
  }
 }
}

static def validate(def bean) {

            //Call other validation methods
 validateNotEmpty(bean) 
}

}

And voila... you can call validate method over any bean using Groovy Categories:

def bean = new FooBeanWithValidations()
use(Validator) {
  bean.validate()
}

Or you can inject a validation method int bean's MetaClass

FooBeanWithValidations.metaClass.validate = {Validator.validate(this)}