Groovy Validator: Ready For Public Consumption

I think the Groovy Validators are ready for public consumption, at least as ready as they’ll ever be.

The basic idea is to allow you to use the same sort of constraints you get with Grails domain objects and use them in Groovy. The main difference is this uses annotations, and Grails uses static blocks.

I have tested them with POGOs, using final and mutable fields, and with immutable objects. Everything seems to work as intended.

Here is the README for the project:

This project has a few annotations that validate fields in POGOs, sort of like Grails constraints.

I will attempt to make some annotations for properties in Groovy.

Here is a POGO:


class Book {

    int pages
    String title
    int year

It’s clean, and has no getters and setters. But what I do not like is there is no validation for your data. What if you want your String to be between 10 and 20 characters? What if you want your int field to be more than 100? And what’s to stop some dingo from trying to create a book object with less than 0 pages?

So I made some annotations that can do some validation for you.


import validation.IntAnnotation
import validation.StringAnnotation

class Book {

    @IntAnnotation( minValue = 30, maxValue = 400, throwEx = false )
    def pages
    @StringAnnotation( minLength = 5, maxLength = 20, regEx = /^.*?[Gg]roovy.*$/  )
    String title
    int year

For POGOs, if a numeric field is declared as “def”, it will become null if the argument does not meet the validation constraints. If it is declared as a primitive, it will be set to 0 if the argument does not meet the validation constraints.

This project can also validate fields in immutable objects. In addition to using the annotations for the fields, you annotate the class with ImmutableValidator:


import validation.ImmutableValidator
import validation.IntAnnotation
import validation.LongAnnotation
import validation.StringAnnotation

class ImmutableObject002 {
    @StringAnnotation( minLength = 5, maxLength = 10 )
    String firstString
    @IntAnnotation( minValue = 10, maxValue = 100 )
    int firstInt
    @LongAnnotation( maxValue = 100L, divisorSet = [ 5L, 7L ] )
    long firstLong

To process the annotations, put your properties in a Map, and add a boolean called “validation” and set it to true (since I couldn’t overload the Map constructor, I added a boolean):

def validatingImObject = new ImmutableObject002( 
    [ firstString: "Hi Again", firstInt: 11, firstLong: 22L ], true )

Adding the “throwEx” will throw an exception if the arguments do not meet the validation constraints. It is optional and is set to false by default. If an exception is thrown, it will print out the value and the constraints.

You might get a message like this:

"Hey" is a String with a length outside the range of 5 and 10 or does not match the regular expression ".*"

You can also use it with immutable objects annotated with the ImmutableValidator annotation. This would be a second boolean after the Map with your properties, since the first boolean controls validation:

def thirdImObject = new ImmutableObject002( 
[ firstString: "Hi Once Again", firstInt: 1234567, firstLong: 222L ], 
true, true )

In that case, you get a message with a line for each field. So you might get a message like this:

Groovy validation exception: 
"eeeeeeeeeee" is a String with a length outside the range of 5 to 10 characters or does not match the regular expression ".*" 
1234567 is an integer outside the range 10 to 100 or it is not divisible by anything in the set [1] 
222 is a long outside the range 0 to 100 or it is not divisible by anything in the set [5, 7]

If “throwException” is true for an immutable object and an exception is thrown, then the object will not be created.

This library can also handle final fields in mutable objects.

import groovy.transform.ToString
import validation.IntAnnotation
import validation.FinalFieldValidator

@ToString( includeNames = true )
class Car {
    @IntAnnotation( minValue = 10, throwEx = false )
    int miles
    @IntAnnotation( minValue = 1990 )
    final int year

As with immutable validation, you need to use a map in the constructor to validate a final field.

def car = new Car( [ miles: 50, year: 2007 ], true, true )

Right now it only handles String, double, float, int and long. For String, it checks the string is checked against a minimum (“minLength”) and maximum (“maxLength”) length, and against a regular expression (“regEx”). For integers and longs, the field is checked against minimum (“minValue”) and maximum (“maxValue”) values, and a set of divisors (“divisorSet”). For double and float, the field is checked against minimum (“minValue”) and maximum (“maxValue”) values. There are defaults for all of these.

To use this project: Run

gradle distZip

and use build/libs/groovy-validator.jar in your project.
You’re welcome.

Image from a 13th century French manuscript at the Burgerbibliothek of Berne  (Wikipedia page here), image from e-Codices, assumed allowed under Fair Use.

2 thoughts on “Groovy Validator: Ready For Public Consumption”

  1. Hi. Great Work! Is there any way we can obtain this using a Maven/Gradle repo with @Grab? If not, do you have that in plans?


  2. At this time, I have no plans for putting this in a repo. I thought I would wait to see if it gains any traction/interest.

    So far, you are the first to comment. Thanks for noticing.

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