Groovy AST transformations, such as @ValueObject and @NonNull, which makes constructing an instance more bullet-proof.

Groovy has the Immutable annotation which allows to create immutable classes, which is a prerequisite for creating value objects. Unfortunately, when a class has been annotated with Immutable it's no longer possible to add your own constructor to verify if provided parameters are not null, making our value objects really bullet-proof.

See Ted Vinke Blog: Make Your Groovy Objects More Bullet-Proof

Bulletproof helps to fill this gap by adding a few AST transformations.

• The NonNull annotation which modifies every constructor to perform null-checks. Add this to an Immutable class and no null slips past your constructor.
• The ValueObject meta-annotation which puts both NonNull and Immutable on your class as a convenience to do above step with one annotation.

• Prerequisites
• Installation
• Annotations
  • @NonNull
  • @ValueObject
• Future Changes

Bulletproof requires Java 7 or later.

Add the bulletproof jar to the classpath in your preferred way and you're set.

@Grab('com.github.tvinke:bulletproof:0.2') 

compile group: 'com.github.tvinke', name: 'bulletproof', version: '0.2'

 <dependency>
    <groupId>com.github.tvinke</groupId>
    <artifactId>bulletproof</artifactId>
    <version>0.2</version>
</dependency>

Consult the bulletproof 0.2 Groovydocs for complete API information.

The NonNull annotation on the class-level triggers an AST transformation which modifies every constructor to perform a null-check.

@groovy.transform.Immutable
@tvinke.bulletproof.transform.NonNull
class Person {
    String name
}
new Person() // throws IllegalArgumentException: "Name can not be null"

The ValueObject meta-annotation combines the Immutable and NonNull annotations, which is used to assist in the creation of value objects.

@tvinke.bulletproof.transform.ValueObject
class Money {
    BigDecimal amount
}

new Money(amount: null) // throws IllegalArgumentException because of NonNull

def money = new Money(2.95)
money.amount = 3.0 // throws ReadOnlyPropertyException because of Immutable

• Consider allowing a mutable object (e.g. default Map constructor, or with TupleConstructor) also to have null-checks performed. In this case probably also through the setters.
• In above case, then probably you need you want to specify which properties need to be null-checked instead of just everything.