Parse an array into an object using GSON

Question

In my application I am using GSON with a JSON from the NASA API.

My intention is to convert that JSON into a class.

Once that is done, I retrieve the data fine... but not all of it.

Here is an abbreviated example of the JSON:

{
    "links": {
      "next": "http://api.nasa.gov/neo/rest/v1/feed?start_date=2015-09-08&end_date=2015-09-09&detailed=false&api_key=DEMO_KEY",
      "previous": "http://api.nasa.gov/neo/rest/v1/feed?start_date=2015-09-06&end_date=2015-09-07&detailed=false&api_key=DEMO_KEY",
      "self": "http://api.nasa.gov/neo/rest/v1/feed?start_date=2015-09-07&end_date=2015-09-08&detailed=false&api_key=DEMO_KEY"
    },
    "element_count": 25,
    "near_earth_objects": {
      "objet_one": [
        {
          "links": {
            "self": "http://api.nasa.gov/neo/rest/v1/neo/2465633?api_key=DEMO_KEY"
          },
          "id": "2465633",
          "neo_reference_id": "2465633",
          "name": "465633 (2009 JR5)",
          "nasa_jpl_url": "http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2465633",
          "absolute_magnitude_h": 20.36,
          "estimated_diameter": {
            "kilometers": {
              "estimated_diameter_min": 0.2251930467,
              "estimated_diameter_max": 0.5035469604
            },
            "meters": {
              "estimated_diameter_min": 225.1930466786,
              "estimated_diameter_max": 503.5469604336
            },
            "miles": {
              "estimated_diameter_min": 0.1399284286,
              "estimated_diameter_max": 0.3128894784
            },
            "feet": {
              "estimated_diameter_min": 738.8223552649,
              "estimated_diameter_max": 1652.0570096689
            }
          },
          "is_potentially_hazardous_asteroid": true,
          "close_approach_data": [
            {
              "close_approach_date": "2015-09-08",
              "close_approach_date_full": "2015-Sep-08 20:28",
              "epoch_date_close_approach": 1441744080000,
              "relative_velocity": {
                "kilometers_per_second": "18.1279547773",
                "kilometers_per_hour": "65260.6371983344",
                "miles_per_hour": "40550.4220413761"
              },
              "miss_distance": {
                "astronomical": "0.3027478814",
                "lunar": "117.7689258646",
                "kilometers": "45290438.204452618",
                "miles": "28142173.3303294084"
              },
              "orbiting_body": "Earth"
            }
          ],
          "is_sentry_object": false
        },
        {
          "links": {
            "self": "http://api.nasa.gov/neo/rest/v1/neo/3426410?api_key=DEMO_KEY"
          },
          "id": "3426410",
          "neo_reference_id": "3426410",
          "name": "(2008 QV11)",
          "nasa_jpl_url": "http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3426410",
          "absolute_magnitude_h": 21.34,
          "estimated_diameter": {
            "kilometers": {
              "estimated_diameter_min": 0.1434019235,
              "estimated_diameter_max": 0.320656449
            },
            "meters": {
              "estimated_diameter_min": 143.4019234645,
              "estimated_diameter_max": 320.6564489709
            },
            "miles": {
              "estimated_diameter_min": 0.0891057966,
              "estimated_diameter_max": 0.1992466184
            },
            "feet": {
              "estimated_diameter_min": 470.4787665793,
              "estimated_diameter_max": 1052.0225040417
            }
          },
          "is_potentially_hazardous_asteroid": false,
          "close_approach_data": [
            {
              "close_approach_date": "2015-09-08",
              "close_approach_date_full": "2015-Sep-08 14:31",
              "epoch_date_close_approach": 1441722660000,
              "relative_velocity": {
                "kilometers_per_second": "19.7498128142",
                "kilometers_per_hour": "71099.3261312856",
                "miles_per_hour": "44178.3562841869"
              },
              "miss_distance": {
                "astronomical": "0.2591250701",
                "lunar": "100.7996522689",
                "kilometers": "38764558.550560687",
                "miles": "24087179.7459520006"
              },
              "orbiting_body": "Earth"
            }
          ],
          "is_sentry_object": false
        }
      ]
  }
}

Well, I have a class called NasaResponse:

class NasaResponse(
    val element_count: Int,
    val neo: near_earth_objects,
    val links: links
)

class links(
    var next: String,
    val previous: String,
    val self: String
)

class near_earth_objects(
    val objeto_uno: ArrayList<NeoItem>,
)

I also have a class called NeoItem with the data I am interested in for each object in the JSON array "object_one".

data class NeoItem(
    val id: Int,
    val name: String,
    val absolute_magnitude_h: Double,
)

The JSON elements such as the "links" (next, previous or self) or the "element_count" can be retrieved without any problem from my activity.

 JsonToClass = gson.fromJson(nasaJson, NasaResponse::class.java)
                Log.d(TAG,, "LINKS: ${JsonToClass?.links?.self}")
                Log.d(TAG, "COUNT: ${{JsonToClass?.element_count}")

My problem is that the "object_one" arrays always return null.

I have tried many possibilities that I have found in support pages or documentation, but without success.

What is the correct way to get those arrays?

Modified, thank you. It was just for the translation for the question on StackOverflow, but the problem remains — Sergio76
– Sergio76, Commented Oct 31, 2022 at 0:15

Android Newbie A · Accepted Answer · 2022-10-31 02:32:56Z

2

The problem is your definition in your custom class does not match the JSON format.

Beside objet_one mentioned in the comment,

you are using neo instead of near_earth_objects as the variable name.

class NasaResponse(
   val element_count: Int,
   val neo: near_earth_objects, // Wrong name, change neo -> near_earth_objects
   val links: links)

To do it better, I recommend to follow the recommended Java/Kotlin style to name the variables.

Then use the annotations provided by GSON to define the name expected to be seen in the JSON.

e.g.

    class NasaResponse(
    @SerializedName("element_count")
    val elementCount: Int,
    @SerializedName("near_earth_objects")
    val nearEarthObjects: NearEarthObjects,
    val links: links)

edited Oct 31, 2022 at 2:32

answered Oct 31, 2022 at 2:12

Android Newbie A

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