Groovy Map to Json String converter

I use Groovy a lot. It’s simple and easy to use, runs on JVM and saves me from Java verbosity. I also like the fact that it’s dynamic.

I use it with a simple Servlet to return data to JavaScript AJAX requests. I like to keep the server side very simple, so I don’t create a lot of POJOs and I’m using HashMaps instead. Groovy has few convenient methods that makes it easy to work with Maps.

I do convert the maps into JSON when returning results to a browser. I don’t use anything fancy, just a couple lines of Groovy code to do that.

class JsonMap {
def toJSON(elements, depth = 0) {
def json = ""
depth.times { json += "\t" }
json += "{"
elements.each { key, value ->
json += "\"$key\":"
json += jsonValue(value, depth)
json += ", "
json = (elements.size() > 0) ? json.substring(0, json.length() - 2) : json
json += "}"
private def jsonValue(element, depth) {
if (element instanceof Map) {
return "\n" + toJSON(element, depth + 1)
if (element instanceof List) {
def list = "["
element.each { elementFromList ->
list += jsonValue(elementFromList, depth)
list += ", "
list = (element.size() > 0) ? list.substring(0, list.length() - 2) : list
list += "]"
return list
(element instanceof String) ? "\"$element\"": element?.toString()
view raw JsonMap.groovy hosted with ❤ by GitHub
class MapToJsonTests extends GroovyTestCase {
private final def mapper = new JsonMap()
void test_convertMapWithListsOfMapsIntoJSON() {
def map = ["a": "a", "b": [["b": "a"], 'd', [12, 12, "e"], ["r": 12]]]
def expected = '''{"a":"a", "b":[
\t{"b":"a"}, "d", ["12", "12", "e"],
def result = mapper.toJSON(map)
assert expected == result

With this code there is quite a bit of assumptions though:

  • it will only work for Map
  • it assumes Strings are used as Map Keys
  • it will convert Maps, Lists and Objects
  • when it meets Object it will call .toString() on it to get it’s value
  • it will try to format it with tabs and new lines a bit, so it’s more pleasant for the eye and human readable

Hope it would be useful for you. Greg

2 thoughts on “Groovy Map to Json String converter

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