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

Question

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.

Just using map and collecting should work cropDetails.stream().map(eachCropMap -> (Map<String, Object>) mapper.convertValue(eachCropJson, HashMap.class)).collect(Collectors.toList()) — Naman
– Naman, Commented Jul 23, 2019 at 9:11

Ryuzaki L · Accepted Answer · 2019-07-23 10:10:25Z

4

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());

edited Jul 23, 2019 at 10:10

answered Jul 23, 2019 at 9:13

Ryuzaki L

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8 Comments

Mohammed Idris Over a year ago

Wouldn't conversion of a JSONArray to a String become a costly operation? If it is not, then I shall use this method. Since I am already using a mapper to convert each Object of JSONArray to a HashMap, I am not sure which approach is better in terms of performance.

Ryuzaki L Over a year ago

I don't think it is a costly operation, toString() should work for that @MohammedIdris, but i gave you the second approach also

Ryuzaki L Over a year ago

still you can avoid this type casting (HashMap<String, Object>) do some google search @MohammedIdris

Mohammed Idris Over a year ago

The first approach seems to work as expected. However, the StreamSupport.stream says the method stream(Spliterator<T>, boolean) is not applicable for the arguments (JSONArray, boolean). Do I use cast (Spliterator<JSONObject>) or (Spliterator<HashMap<String,Object>>)? Also, Is Type Casting a bad idea? @Deadpool

Mohammed Idris Over a year ago

It works as expected with the updated answer. Thanks @Deadpool

|

SUMIT NAVIN · Accepted Answer · 2019-07-23 09:29:23Z

2

Using stream this can be done

List<HashMap<String, Object>> output = cropDetails.toList().stream().map(m -> ((HashMap<String, Object>) m)).collect(Collectors.toList());

answered Jul 23, 2019 at 9:29

SUMIT NAVIN

212 bronze badges

2 Comments

Mohammed Idris Over a year ago

cropDetails is a JSONArray. toList() function is undefined for type JSONArray. @SUMIT NAVIN

Mohammed Idris Over a year ago

Using stream on cropDetails JSONArray gave me the expected result.

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