Convert JSONArray to List<HashMap<String,Object>> in java without GSON

Mohammed Idris :

I have a JSONArray from net.minidev.json which I want to convert to List<HashMap<String,Object>>.

There are many answers for converting the JSONArray using Gson.

However, I cannot add Gson as a dependency to my pom.xml, so I am looking for a way to achieve it with Java-8 features.

My JSONArray is something like this: It comprises multiple hierarchies.

[
  {
    "data": {
      "name": "idris"
    },
    "children": [
      {
        "processStandardDeduction": 69394,
        "cropId": 1,
        "data": null,
        "expectedQuantityPerAcre": 1220,
        "name": "Red Tomato 1 quality",
        "id": 1003,
        "autoArchivePlotDays": 59902
      },
      {
        "processStandardDeduction": 69394,
        "cropId": 1,
        "autoArchivePlotDays": 59902
      },
      {
        "processStandardDeduction": 69394,
        "cropId": 1,
        "autoArchivePlotDays": 59902
      }
    ],
    "name": "Red Tomato",
    "id": 1002
  },
  {
    "data": null,
    "name": "Red Tomato 1 quality",
    "id": 1003,
    "processStandardDeduction": 69394,
    "cropId": 1,
    "expectedQuantityPerAcre": 1220,
    "cropName": "Tomato",
    "autoArchivePlotDays": 59902
  },
  {
    "data": null,
    "name": "Red Tomato 3 quality",
    "id": 1001,
    "processStandardDeduction": 69394,
    "autoArchivePlotDays": 59902
  },
  {
    "processStandardDeduction": 69394,
    "cropId": 1,
    "data": null,
    "id": 1004,
    "autoArchivePlotDays": 59902
  }
]

I would like to achieve same structure in List>

I tried looping each element of the JSONArray by converting it to each HashMap<String,Object> and then adding it to the List<HashMap<String,Object>>.

ObjectMapper mapper = new ObjectMapper();
List<HashMap<String, Object>> cropDetailsList = new ArrayList<>();
        for (Object eachCropJson : cropDetails) { //cropDetails is the JSONArray

            HashMap<String, Object> eachCropMap = (HashMap<String, Object>) mapper.convertValue(eachCropJson,
                    HashMap.class);
            cropDetailsList.add(eachCropMap);
        }
return cropDetailsList;

I would like to try a better approach using Java-8 features without using a forEach. Thanks in advance.

Deadpool :

If you get this JSON as String then you can use ObjectMapper.readValue method

readValue(String content, TypeReference valueTypeRef)

Code

List<HashMap<String, Object>> cropDetailsList = mapper.readValue(jsonString,
                                   new TypeReference<List<HashMap<String, Object>>>(){});

In the same way if you want to iterate JSONArray

List<HashMap<String, Object>> cropDetailsList = cropDetails.stream()
            .map(eachCropJson->(HashMap<String, Object>) mapper.convertValue(eachCropJson, HashMap.class))
            .collect(Collectors.toList());