spark.groovy

@Grab('com.sparkjava:spark-core:2.1')

import static spark.Spark.*
import groovy.json.JsonBuilder

Object.metaClass.asJson = {
    def builder = new JsonBuilder(delegate);
    builder.toString()
}

def map = [:]
map['foo'] = 'ハローワールド'
map['bar'] = [1, 2, 3]
map['boo'] = ['hoge' : 'aaa', 'fuga' : [1, 2, ['obj':true]]]

get('/map', { req, res -> map.asJson() })