CODEWITHSUNDEEP
javajsongson
snaggs
snaggs

Reputation: 5713

How to convert automatically list of objects to JSONArray with Gson library in java?

Lets say I have following list of custom object: ArrayList<GroupItem> where GroupItem is some class that has int and String variables.

I tried so far Gson library but it's not exactly what I want.

ArrayList<GroupItem> groupsList = /* ... */
Gson gson = new Gson();
JsonElement element = gson.toJsonTree(groupsList, new TypeToken<ArrayList<GroupItem>>() {}.getType());

JsonArray jsonArray = element.getAsJsonArray();

My goal is to get JSONArray (org.Json.JSONArray) somehow. Any ideas?

[EDIT]

My project is Android with Cordova that has API based on org.Json.JSONArray

ANd I thought to write some generic way to convert instances to JSONArray / JSONObject

Thanks,

Upvotes: 12

Views: 76806

Answers (5)

Ronald Coarite
Ronald Coarite

Reputation: 4726

Use Jackson for JSON to Object or Object to JSON

See the next link Jackson examples

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);
StringWriter stringWriter = new StringWriter();
objectMapper.writeValue(stringWriter, groupsList );
System.out.println("groupsList JSON is\n"+stringWrite);

Upvotes: 3

Brian Roach
Brian Roach

Reputation: 76898

The org.json based classes included in Android don't have any features related to converting Java POJOs to/from JSON.

If you have a list of some class (List<GroupItem>) and you absolutely need to convert that to a org.json.JSONArray you have two choices:

A) Use Gson or Jackson to convert to JSON, then parse that JSON into a JSONArray:

List<GroupItem> list = ...
String json = new Gson().toJson(list);
JSONArray array = new JSONArray(json);

B) Write code to create the JSONArray and the JSONObjects it will contain from your Java objects: 

JSONArray array = new JSONArray();
for (GroupItem gi : list)
{
    JSONObject obj = new JSONObject();
    obj.put("fieldName", gi.fieldName);
    obj.put("fieldName2", gi.fieldName2);
    array.put(obj);
}

Upvotes: 7

snaggs
snaggs

Reputation: 5713

This way is worked for me:

Convert all list to String.

String element = gson.toJson(
                    groupsList,
           new TypeToken<ArrayList<GroupItem>>() {}.getType());

Create JSONArray from String:

    JSONArray list = new JSONArray(element);

Upvotes: 22

jeremyjjbrown
jeremyjjbrown

Reputation: 8009

Why do you want to use GSON to convert to an org.json class? Nor do you need to write any custom code to get a JSONArray. The org.json api provides a way to do it.

  LinkedList list = new LinkedList();
  list.add("foo");
  list.add(new Integer(100));
  list.add(new Double(1000.21));
  list.add(new Boolean(true));
  list.add(null);
  JSONArray jsonArray = new JSONArray(list);
  System.out.print(jsonArray);

Upvotes: 3

weston
weston

Reputation: 54781

You don't need gson. There's a constructor that takes a collection, so just:

ArrayList<GroupItem> groupsList =... ;
JSONArray JSONArray = new JSONArray(groupsList);

Upvotes: 1

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