JSON to Groovy parser

Question

I found many things about converting Groovy to JSON, but oddly enough, not the other way.

What is the (best) JSON to Groovy parser around there ?

Answer 1

Because compiled Groovy classes are compatible with Java classes, you should be able to use any Java library for converting JSON to POJOs (or POGOs). Jackson is a fairly popular choice which you can use to convert JSON like this:

String json = '{
  "name" : { "first" : "Joe", "last" : "Sixpack" },
  "gender" : "MALE",
  "verified" : false,
  "userImage" : "Rm9vYmFyIQ=="
}'

to a Map using:

Map<String,Object> userData = mapper.readValue(json, Map.class)

Or if you want to convert the JSON to a Groovy User class:

User userData = mapper.readValue(json, User.class)

This will map properties in the Groovy class to keys in the JSON.

Answer 2

If you are on Groovy 1.8 or later, there is a build in JsonSlurper you can use this way:

import groovy.json.JsonSlurper

//Attention: you have to use double quotes inside the json string
def jsonObj = new JsonSlurper().parseText( '{ "name":"Peter", "age": 23}' )

assert jsonObj.name == "Peter"
assert jsonObj.age == 23
//this won't work, because it's not defined
assert jsonObj.gender == null

Answer 3

I use JSON-lib in HTTPBuilder, but I use the JSONSlurper class to parse a string to a JSON instance:

JSON jsonMapObject = new JsonSlurper().parse( "{integer:1, bool: true}" );

To go from Object to JSON, I do this:

//from a map:
new JSONObject().putAll( [one:'1', two:'two']).toString()
//from an object:
JSONObject.fromObject( somePOGO ).toString()

Answer 4

To the people having trouble with json-lib and GJson.enhanceClasses(). Try GJson.enhanceString() instead.

GJson.enhanceString()
def o = "{\"x\": 20.0}" as JSONObject

Answer 5

JSON-lib claims to be able to transform POGO to JSON and back. If POGO means what I think it does (Plain Old Groovy Object), you're set :).

They give this example:

def strAsJsonObject = "{integer:1, bool: true}" as JSONObject

Update:

I've tried the lib myself, this is the complete code:

import net.sf.*;
import net.sf.json.*;
import net.sf.json.groovy.*;

println "hi"
GJson.enhanceClasses()
def strAsJsonObject = "{integer:1, bool: true}" as JSONObject
println strAsJsonObject

It'll chase you through a marathon of downloading dependencies (ezmorph, commons lang, commons logger) and once you've resolved them all, this is what you get:

Exception in thread "main" org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object '{integer:1, bool: true}' with class 'java.lang.String' to class 'net.sf.json.JSONObject'

According to The mailing list, you get this for not calling GJsonlib.enhanceClasses(), but I did call that, as you can see above.

I've concluded that it's a worthwhile endeavor to hate Groovy's JSON-lib.