Read single value from nested object using Gson in Java

Question

Below is my Json. I want to get the value of "Id" inside "Details" using Gson

{
    "name": "testAutomation-1",
    "owner": "TestUSer",
    "description": "testAutomation-1",
    "subSet": [
        "test-audit"
    ],
    "labels": "{\"engagementType\":\"Sx\",\"type\":\"collect\"}",
    "createdTime": 1548508294790,
    "updatedTime": 1548654725381,
    "scheduleDateTime": null,
    "timeZone": null,
    "jobStatus": "Report-Requested",
    "loggedInUser": null,
    "Details": [
        {
            "Status": "Completed",
            "Id": "fe1f6b40-216b-11e9-a769-25be4c5889e7"
        }
    ]
}

I created a map using the below code. But not sure how to get the value

Map<String, Object> createmap = new HashMap<String, Object>();
Gson gson = new Gson();
Type type = new TypeToken<Map<String, Object>>(){}.getType();
createmap = gson.fromJson(jsonobj.toString(), type);

you can access it using below line System.out.println(((List<Map<String,Object>>)createmap.get("Details")).get(0).get("Id")) — Pramod
– Pramod, Commented Jan 28, 2019 at 12:41

Thibstars · Accepted Answer · 2019-01-28 17:20:11Z

2

Assuming that you need the first element of the array, you could do something like this (knowing that DATA is the JSon String you provided):

Map<String, JsonElement> resultMap;
Gson gson = new Gson();
Type type = new TypeToken<Map<String, JsonElement>>() {}.getType();
JsonElement jsonElement = gson.fromJson(DATA, JsonElement.class);
resultMap = gson.fromJson(jsonElement.toString(), type);

JsonArray details = resultMap.get("Details").getAsJsonArray();
JsonObject recordElement = details.get(0).getAsJsonObject();
System.out.println(recordElement.get("Id").getAsString());

All this does is fetch the Details array as a JsonArray and it fetches the value of the Id element afterwards.

Since you seem to be dealing with a UUID, you could maybe benefit from using:

UUID uuid = UUID.fromString(recordElement.get("Id").getAsString());

edited Jan 28, 2019 at 17:20

answered Jan 28, 2019 at 12:45

Thibstars

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Comments

Anitha.R · Accepted Answer · 2019-01-28 12:56:46Z

0

As per Gson guide, you need to use the correct parameterized type instead of your generic type. Then you can easily access the value you need from the map.

Map<String, Dummy> map = new HashMap<String, Dummy>();
Type t = new TypeToken<Map<String, Dummy>>() {}.getType();
map = new Gson().fromJson(jsonobj.toString(), type);

Then you can get the map value (map.get("details") and read the id from that.

answered Jan 28, 2019 at 12:56

Anitha.R

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Comments

pirho · Accepted Answer · 2019-01-28 15:37:24Z

In your JSON Details is a list or an array. So there is not just one id in some cases and you should prepare for that also.

It is usually also a good habit to create DTOs to describe data, so like two below classes:

Data

@Getter
public class Data {
    // Recommendation, in Java field name should start lower case
    @SerializedName("Details")
    List<Detail> details; // Could be some List also
}

Detail

@Getter
public class Detail {
    // Recommendation, in Java field name should start lower case
    @SerializedName("Id")
    private UUID id;
}

This also allows later to flexibly pick up any other fields you need from the same JSON.

Serialize your JSON like:

Data data = gson.fromJson(YOUR_JSON, Data.class);

Check the ids - for example - like:

data.getDetails().forEach(d -> log.info("{}", d.getId()));

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