How to convert map of JSON objects to JSON using GSON in Java?

Question

I have a map of JSON objects as follows:

Map<String,Object> map = HashMap<String,Object>();
map.put("first_name", "prod");
JSONObject jsonObj = new JSONObject("some complex json string here");
map.put("data", jsonObj);

Gson gson = new Gson();
String result = gson.toJson(map);

Now if the "some complex JSON string here" was:

{"sender":{"id":"test test"},"recipients":{"id":"test1 test1"} }

and execute above code gives me something like:

{
    "first_name": "prod",
    "data": {
        "map": {
            "sender": {
                "map": {
                    "id": "test test"
                    }
                }
            },
            "recipients": {
                "map": {
                    "id": "test1 test1"
                }
            }
        }
    }
}

I might have some syntax error up there, but basically I don't know why I am seeing objects wrapped around map 's.

Update

according to comments, it is a bad idea to mix different json parsers. i can understand that. but my case requires calling an external api which takes a hash map of objects that are deserialized using gson eventually.

is there any other object bedsides JSONObject that i can add to the map and still have gson create json out of it without extra 'map' structure? i do understand that i can create java beans and achieve this. but i'm looking for a simpler way since my data structure can be complex.

Update2

going one step back, i am given a xml string. and i have converted them to json object. now i have to use an external api that takes a map which in turn gets converted to json string using gson in external service.

so i am given an xml data structure, but i need to pass a map to that function. the way i have described above produces extra 'map' structures when converted to json string using gson. i do not have control to change how the external service behaves (eg using gson to convert the map).

Answer 1

This has to do with the internal implementation of JSONObject . The class itself has an instance field of type java.util.Map with the name map .

When you parse the String

{"sender":{"id":"test test"},"recipients":{"id":"test1 test1"} }

with JSONObject , you actually have 1 root JSONObject , two nested JSONObject s, one with name sender and one with name recipients .

The hierarchy is basically like so

JSONObject.map ->
    "sender" -> 
            JSONObject.map ->
                    "id" -> "test test",
    "recipients" ->
            JSONObject.map ->
                    "id" -> "test test1"

Gson serializes your objects by mapping each field value to the field name.

---

Listen to this man.

And this one.

Answer 2

Mixing classes from two different JSON libraries will end in nothing but tears. And that's your issue; JSONObject is not part of Gson. In addition, trying to mix Java data structures with a library's parse tree representations is also a bad idea; conceptually an object in JSON is a map.

If you're going to use Gson, either use all Java objects and let Gson convert them, or use the classes from Gson:

JsonObject root = new JsonObject();
root.addProperty("first_name", "prod");

JsonElement element = new JsonParser().parse(complexJsonString);
root.addProperty("data", element);

String json = new Gson().toJson(root);

Answer 3

I'd a similar problem and I finally resolved it using json-simple .

HashMap<String, Object> object = new HashMap<String,Object>;

// Add some values ...

// And finally convert it
String objectStr = JSONValue.toJSONString(object);

Answer 4

You may try out the standard implementation of the Java API for JSON processing which is part of J2EE .

JsonObject obj = Json
    .createObjectBuilder()
    .add("first_name", "prod")
    .add("data", Json.createObjectBuilder()
    .add("sender", Json.createObjectBuilder().add("id", "test test"))
    .add("recipients", Json.createObjectBuilder().add("id", "test1 test1"))).build();

Map<String, Object> prop = new HashMap<String, Object>() {
    {
        put(JsonGenerator.PRETTY_PRINTING, true);
    }
};
JsonWriter writer = Json.createWriterFactory(prop).createWriter(System.out);
writer.writeObject(obj);
writer.close();

The output should be:

{
    "first_name":"prod",
    "data":{
        "sender":{
            "id":"test test"
        },
        "recipients":{
            "id":"test1 test1"
        }
    }
}