Working with JSON

JSON support is built in (groovy.json) — no extra library needed.

Parsing

import groovy.json.JsonSlurper

def text = '''
{
  "name": "tools-api",
  "version": "2.1.0",
  "private": false,
  "maintainers": [
    {"name": "Ada", "email": "ada@example.com"},
    {"name": "Linus", "email": null}
  ],
  "limits": {"rps": 50, "burst": 120}
}
'''

def json = new JsonSlurper().parseText(text)
println json.name
println json.maintainers*.name
println json.maintainers.find { !it.email }.name
println json.limits.rps * 2
println json.private.getClass().simpleName

tools-api
[Ada, Linus]
Linus
100
Boolean

JsonSlurper turns JSON objects into maps and arrays into lists, so you navigate with the same syntax as any Groovy data. It also has parse(File) and parse(URL).

Generating

import groovy.json.JsonOutput

def data = [
    id: 7,
    tags: ['groovy', 'json'],
    owner: [name: 'Ada', active: true],
    score: 9.5,
    note: null,
]

println JsonOutput.toJson(data)
println JsonOutput.prettyPrint(JsonOutput.toJson(data))

{"id":7,"tags":["groovy","json"],"owner":{"name":"Ada","active":true},"score":9.5,"note":null}
{
    "id": 7,
    "tags": [
        "groovy",
        "json"
    ],
    "owner": {
        "name": "Ada",
        "active": true
    },
    "score": 9.5,
    "note": null
}

Paste JSON into the JSON Formatter or JSON Validator when you need to inspect it.

JsonBuilder

import groovy.json.JsonBuilder

def users = [[name: 'Ada', roles: ['admin']], [name: 'Linus', roles: []]]

def builder = new JsonBuilder()
builder {
    count users.size()
    items(users.collect { u ->
        [name: u.name, admin: 'admin' in u.roles]
    })
    meta {
        generator 'groovy'
    }
}
println builder.toString()

{"count":2,"items":[{"name":"Ada","admin":true},{"name":"Linus","admin":false}],"meta":{"generator":"groovy"}}

JsonBuilder uses closures and method calls to describe the structure — you'll see this builder pattern again in the next lessons.

Objects to JSON and back

import groovy.json.*

class Task { String title; boolean done; List<String> tags }

def task = new Task(title: 'Write docs', done: false, tags: ['docs'])
def jsonText = JsonOutput.toJson(task)
println jsonText

def copy = new JsonSlurper().parseText(jsonText) as Task
println "${copy.title} / ${copy.tags}"

def gen = new JsonGenerator.Options()
    .excludeNulls()
    .excludeFieldsByName('done')
    .build()
println gen.toJson(new Task(title: 'Ship'))

{"title":"Write docs","done":false,"tags":["docs"]}
Write docs / [docs]
{"title":"Ship"}

JsonGenerator.Options customizes output — skip nulls, exclude fields, format dates, or add converters for your own types. For large applications, Jackson (usually via your framework) is the common choice, and works from Groovy exactly as from Java.