The other day I blogged about generating XML from domain classes in Grails. Today I want to show how to do the same thing but with JSON instead. JSON is widely used and accepted as a great way to exchange information in AJAX and RESTful applications, and Grails makes it mind-numbingly simple to do this.

Grails provides a class called grails.converters.JSON. This class provides a DSL, or Domain Specific Language, for creating JSON, as well as automatic marshaling of objects to JSON. In this sample I will demonstrate the automatic marshaling technique, and show how to return the JSON string back to the view, and even how to render it to the HTTP output for AJAX applications. For the sake of demonstration let’s pretend I have a Person domain class, and I get a list of all the records from the database. With this list of persons I want to build an XML file that looks like this.

[
	{"class":"com.adampresley.groovy.Person","id":1,"email":"nec.tempus.scelerisque@montesnascetur.ca","firstName":"Imogene","lastName":"Coffey"},
	{"class":"com.adampresley.groovy.Person","id":2,"email":"malesuada.malesuada.Integer@vitae.ca","firstName":"Marsden","lastName":"Mcbride"},
	{"class":"com.adampresley.groovy.Person","id":3,"email":"neque.venenatis@ipsum.edu","firstName":"Jescie","lastName":"Vang"},
	{"class":"com.adampresley.groovy.Person","id":4,"email":"Nullam@MorbimetusVivamus.org","firstName":"August","lastName":"Hewitt"},
	{"class":"com.adampresley.groovy.Person","id":5,"email":"Sed@mollisInteger.org","firstName":"Raven","lastName":"Gilmore"}
]

A pretty simple JSON structure. Now let’s look at that Person domain class. You may remember this from my Grails and XML post.

package com.adampresley.groovy

class Person {
	String firstName
	String lastName
	String email = ""

	static constraints = {
		firstName(blank: false)
		lastName(blank: false)
	}

	@Override
	public String toString() {
		"${firstName} ${lastName}"
	}
}

Nothing has changed here. Now let’s see how we can use the power of Grails to easily transform an array of Person objects into JSON data.

package com.adampresley.groovy

import grails.converters.JSON

class TransformationsController {
	def json = {
		def persons = Person.list()
		println (persons as JSON)
		[ personJSON: (persons as JSON) ]
	}

	def renderJson = {
		def persons = Person.list()
		render (persons as JSON)
	}
}

The above controller has two methods, one for returning a JSON string, and the other renders JSON to the HTTP output. As you can see it is quite possibly the simplest thing you’ve ever done in your life. Cheers and happy coding!