In Gson, how do I add a JsonArray to a JsonObject?

Question

Suppose that I am trying to get a Json structure like this:

{
  "rows": [
    {
      "date_str": "2016-07-01",
      "sleep_7_or_more_hours": true,
      "activity_minutes": "0",
      "water_5_or_more_cups": true,
      "fruit_veg_4_or_more_servings": true,
      "physical_activity_description": "walking"
    }
    {
      "date_str": "2016-07-02",
      "sleep_7_or_more_hours": true,
      "activity_minutes": "30",
      "water_5_or_more_cups": true,
      "fruit_veg_4_or_more_servings": true,
      "physical_activity_description": "walking"
    }  
    ...etc  
  ]
}

Some questions about building this Json:

How can I specify the name of the JsonArray? I need it to be named, in the Json, "rows".
How can I add the JsonArray rows to a JsonObject (I assume that's what the outer brackets mean)?

This is the code that I am using to do it:

JsonArray rows = new JsonArray();

//Code to get local dates omitted
for (LocalDate date = start; !date.isAfter(end); date = date.plusDays(1))
{
    JsonObject row = new JsonObject();

    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-mm-dd", Locale.ENGLISH);
    String dateString = date.format(formatter);
    row.addProperty("date_str", dateString);

    boolean sleptLongEnough = (sleepLog.getTimeInBed(getDate(date)) > (7 * 60));
    row.addProperty("sleep_7_or_more_hours", sleptLongEnough);

    int activityMinutes = (activitiesLog.getMinutesVeryActive(getDate(date)) + activitiesLog.getMinutesFairlyActive(getDate(date)));
    ...
    //Omitted extra code
    rows.add(row);
}
JsonObject logs = new JsonObject();
//add rows to logs here.

I need to add rows to logs. However, JsonObject only appears to have .add(JsonElement) and .addProperty(String, variousTypes), and nothing to add an array. What am I missing?

EDIT: I am not using Gson to serialize objects because the Json is composed of data items from each of several logs (and not even close to all of the information in each log).

You are using Gson, so why are you manually building JSON and not using Java class serialization? — OneCricketeer, Jul 28 '16 at 17:26
@cricket_007 Because the classes look nothing like the Json I am building. See my edit. — Cache Staheli, Jul 28 '16 at 17:26
@Maraboc I knew I was missing something simple. If you want to put that into an answer, I'll accept it. — Cache Staheli, Jul 28 '16 at 17:33
Possible duplicate of [How to create correct JSONArray in Java using JSONObject](https://stackoverflow.com/questions/18983185/how-to-create-correct-jsonarray-in-java-using-jsonobject) — Rajat, Apr 08 '19 at 07:15

score 29 · Accepted Answer · answered Jul 28 '16 at 17:33

29

JsonArray is an instance of JsonElement. So the method .add("name", element), where element is a JsonArray, should just work.

answered Jul 28 '16 at 17:33

thewmo

755
5
7

1

BTW, `JsonArray` **extends** `JsonElement`, not an instance – Jeeter Jul 28 '16 at 17:37
2

Yes, to be more verbose, an instance of JsonArray is also an instance of JsonElement, by virtue of their subclass/superclass relationship. – thewmo Jul 28 '16 at 17:40

score 2 · Answer 2 · answered Jul 28 '16 at 17:33

2

You can use the method JsonObject.add() to add a JsonElement, which JsonArray inherits from:

logs.add("rows", rows)

And then when deserializing it out, you can just cast it back to a JsonArray

answered Jul 28 '16 at 17:33

Jeeter

5,887
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In Gson, how do I add a JsonArray to a JsonObject?

2 Answers2

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