Converting string to JSONArray, and then to list

Question

I have String "[{...}]" and I want convert it to JSONArray, and then to List list = new List I was trying this solution, and this is my code

public void RestoreData()
{
    String toConvert = "[{...}]" // I don't place full String, but it's typical JSONArray, but in String
    ArrayList<myClass> listdata = new ArrayList<myClass>();
    JsonObject jsonObject = new JsonObject();
    JSONArray jArray = (JSONArray)jsonObject;
    if (jArray != null) {
        for (int i=0;i<jArray.length();i++){
            listdata.add(jArray.getString(i));
        }
    }
}

And when I'm trying to compile this I get 2 errors:

In JSONArray jArray = (JSONArray)jsonObject; I get error 'Incovertible types; cannot cast 'org.json.JSONObject' to 'org.json.JSONArray'.
And second: in listdata.add(jArray.getString(i)); I get error 'unhandled exception org.json.JSONException'.

I'm new in Java and I work with Json for the first time.

EDIT A small truncated example of the Json string:

[{"lootArmorGain":0,"lootBlockGain":0,"lootCost":93500,"lootCritGain":2,"lootCritPowerGain":0,"lootDamageAbsorptionGain":0,"lootDamageGain":0, }]

yes some part of string so that we can check it, if it is valid data or not. — Alok
– Alok, Commented May 5, 2018 at 17:41
Please give a small (truncated) example of the string you say is a "... typical JSONArray". — Barns
– Barns, Commented May 5, 2018 at 17:48
Now we need to know what myClass is. By-the-way in java naming convention methods do not use capitalization... however, Classes are capitalized. — Barns
– Barns, Commented May 5, 2018 at 17:51

Levi Moreira · Accepted Answer · 2018-05-05 18:29:23Z

3

I think what you want is:

public void RestoreData()
{
   try{
    String toConvert = "[{...}]" // I don't place full String, but it's typical JSONArray, but in String
    ArrayList<MyClass> listdata = new ArrayList<MyClass>();
    JSONArray jsonArray = new JSONArray(toConvert); 

    if (jsonArray != null) {
       Gson gson = new Gson();
        for (int i=0;i<jsonArray.length();i++){
            String json = jsonArray.getJSONObject(i).toString();
            MyClass obj = gson.fromJson(json, MyClass.class);
            listdata.add(obj);
        }
    }
    }catch(JSONException e){
          e.printStackTrace();
    }
}

To convert from JSONOject to your custom class use GSON, see above.

 compile 'com.google.code.gson:gson:2.8.4'

Note that your custom class need to have an empty constructor as well as getters and setters in order to make gson work.

edited May 5, 2018 at 18:29

answered May 5, 2018 at 17:39

Levi Moreira

12k4 gold badges35 silver badges49 bronze badges

Sign up to request clarification or add additional context in comments.

12 Comments

Hubizonek Over a year ago

i got again "unhandled exception org.json.jsonexception". on this code "JSONArray(toConvert)"

Levi Moreira Over a year ago

it means your String is probably a not valid json array as you said

Hubizonek Over a year ago

Ohhh yea, sorry, i made mistake.. look at my question now. I want to conver to ArrayList<Object>

Levi Moreira Over a year ago

No problem, some people don't understand that if they downvote someone it is polite to explain why :/

Barns Over a year ago

I agree @LeviAlbuquerque. I just don't understand people down voting valid answers without at least saying why it was down voted. Maybe that person will eventually get up some courage to explain themselves! An Up vote to compensate.

|

Khemraj Sharma · Accepted Answer · 2018-05-05 18:17:38Z

1

I think best approach will be using Google Gson Library.

String toConvert = "[{...}]"
Type listType = new TypeToken<List<myClass>>() {}.getType();
List<myClass> yourList = new Gson().fromJson(toConvert, listType);

You dont need to get each position manually.

answered May 5, 2018 at 18:17

Khemraj Sharma

59.1k30 gold badges215 silver badges229 bronze badges

Comments

Levi Moreira · Accepted Answer · 2018-05-05 17:50:01Z

0

For simplicity you can also use Jackson api

ObjectMapper objectMapper = new ObjectMapper();
TypeFactory typeFactory = objectMapper.getTypeFactory();
List<SomeClass> someClassList = objectMapper.readValue(jsonString,typeFactory.constructCollectionType(List.class, SomeClass.class));

edited May 5, 2018 at 17:50

Levi Moreira

12k4 gold badges35 silver badges49 bronze badges

answered May 5, 2018 at 17:47

Naveen

83010 silver badges19 bronze badges

2 Comments

Hubizonek Over a year ago

How to use this? I must write something build.gradle? what?

Naveen Over a year ago

you must add dependency of jackson api in your build.gralde ( just like another dependency and use the above code )

Collectives™ on Stack Overflow

Converting string to JSONArray, and then to list

3 Answers 3

12 Comments

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

12 Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related