public static List<Product> getCartList() {

    JSONObject responseDetailsJson = new JSONObject();
    JSONArray jsonArray = new JSONArray();

    List<Product> cartList = new Vector<Product>(cartMap.keySet().size());
    for(Product p : cartMap.keySet()) {
        cartList.add(p);
        JSONObject formDetailsJson = new JSONObject();
        formDetailsJson.put("id", "1");
        formDetailsJson.put("name", "name1");
       jsonArray.add(formDetailsJson);
    }
    responseDetailsJson.put("forms", jsonArray);//Here you can see the data in json format

    return cartList;

}

you can get the data in the following form

{
    "forms": [
        { "id": "1", "name": "name1" },
        { "id": "2", "name": "name2" } 
    ]
}

You need an external library for this.

JSONArray jsonA = JSONArray.fromObject(mybeanList);
System.out.println(jsonA);

Google GSON is one of such libraries

You can also take a look here for examples on converting Java object collection to JSON string.

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);
}

You can also direct use

 String jsonString = new ObjectMapper().writeValueAsString(jsonObjectList) 

To get the desired ouptput

Here is the small example

List<JSONObject> jsons = new ArrayList<>();
jsons.add(new JSONObject(ImmutableMap.of("Attribute", "EmailAddress", "Value", "[email protected]")));
jsons.add(new JSONObject(ImmutableMap.of("Attribute1", "EmailAddress3", "Value1", "[email protected]")));
System.out.println(new ObjectMapper().writeValueAsString(jsons));

The output is

[{"Value":"[email protected]","Attribute":"EmailAddress"},{"Attribute1":"EmailAddress3","Value1":"[email protected]"}]

I suspect there are some toString() method in any object that you have override?

For any one who looks for answer yet:

1.Add jackson-databind library to your build tools like Gradle or Maven

2.in your Code:

ObjectMapper mapper = new ObjectMapper();

List<Student> studentList = new ArrayList<>();

studentList = Arrays.asList(mapper.readValue(jsonStringArray, Student[].class));

I got correct result using the code below. Can you highlight if you are doing something different? Maybe I can make similar changes and try once.

public static void main(String[] args){
    HashSet<String> users = new HashSet<>(); 
    users.add("user1");
    users.add("user2");

    JSONObject j = new JSONObject();
    j.put("users", users);
    System.out.println(j.toString(2));        
}

Output:

{"users": [ "user2", "user1" ]}

================================== EDIT =================================

I think I figured what the problem was. Please try the following code and let us know if that worked.

public static void main(String[] args) {
    JSONObject o1 = new JSONObject();
    o1.put("1", new User("User1"));
    JSONObject o2 = new JSONObject();
    o2.put("2", new User("User2"));

    HashSet<JSONObject> users = new HashSet<>(); 
    users.add(o1);
    users.add(o2);

    JSONObject j = new JSONObject();
    j.put("users", users);
    System.out.println(j.toString(2));        
}