Groovy for Domain-specific Languages - Second Edition

Chapter 7

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Conveniently, this pattern is the same as the one used in Groovy categories, which
means that the Apache Commons Lang Util classes can all be dropped straight into
a use block. So all of these useful utility classes are ready to be used in your Groovy
code as categories:

import org.apache.commons.lang.StringUtils

expect:

use (StringUtils) {

"org.apache.commons.lang3".split(".") ==

["org", "apache", "commons", "lang3"]

}

You can also use the @Category annotation in association with

a class.

Traits

A recent and very useful addition to the Groovy language is the concept of a trait.
A trait is a reusable set of methods and properties that can be applied to any class
without the need for multiple inheritance. Earlier in the chapter, we implemented a
pretty print class for the Customer class. In the following example we implement the
PrettyPrintable class as a trait. This trait can be applied to any class to give it the
ability to pretty print its properties:

trait PrettyPrintable {

void prettyPrint() {

this.properties.sort { it.key }.each {

if (it.key != 'prettyPrint' && it.key != 'class')

println it.key + ": " + it.value

}

}

}

class Customer implements PrettyPrintable {

int id

String firstName

String surname

String street

String city

}