How to customize a json that is created using Gson object in java

You need to create instance updateJsonObj of JsonObject to update key and value of columnMap using for each loop. Following code snippet is the solution :

String json = "{ \"data\": {\"isDeleted\": false,\"period\": 201601,"
            + "\"columnMap\": {\"1c49eb80-7b53-11e6-bc4b-afbeabb62718\": \"5000\","
            + "\"1c49eb80-7b52-11e6-bc4b-afbeabb62718\": \"hello\","
            + "\"03a534c0-a7f1-11e6-9cde-493bf5c47f4\": \"AUS\", "
            + "\"03a534c0-a7fa-11e6-9cde-493bf5c47f4\": \"123\"}}}";

    Gson gson = new Gson();
    JsonObject root = new JsonParser().parse(json).getAsJsonObject();
    JsonElement dataElement = root.get("data");
    // cobj has value of colummMap of json data
    JsonObject cobj = (JsonObject) root.get("data").getAsJsonObject().get("columnMap");
    JsonObject updateJsonObj = root;
    // remove columnMap node as you wanted !
    updateJsonObj.get("data").getAsJsonObject().remove("columnMap");

    for (Entry<String, JsonElement> e : cobj.entrySet()) {
         //update updateJsonObj root node with key and value of columnMap
         updateJsonObj.get("data").getAsJsonObject().addProperty(e.getKey(), e.getValue().getAsString());
    }

    String updateJson = gson.toJson(updateJsonObj);
    System.out.println(updateJson);