How to convert ArrayList of custom class to JsonArray in Java?

Question

I am trying to convert ArrayList of custom class to JsonArray. Below is my code. It executes fine but some JsonArray elements come as zeros even though they are numbers in the ArrayList. I have tried to print them out. Like customerOne age in the ArrayList is 35 but it is 0 in the JsonArray. What could be wrong?

    ArrayList<Customer> customerList = CustomerDB.selectAll();
    Gson gson = new Gson();

    JsonElement element = 
     gson.toJsonTree(customerList , new TypeToken<List<Customer>>() {}.getType());

    JsonArray jsonArray = element.getAsJsonArray();

Ahsan Mahboob Shah · Accepted Answer · 2020-05-28 06:09:24Z

45

Below code should work for your case.

List<Customer> customerList = CustomerDB.selectAll();

Gson gson = new Gson();
JsonElement element = gson.toJsonTree(customerList, new TypeToken<List<Customer>>() {}.getType());

if (! element.isJsonArray() ) {
// fail appropriately
    throw new SomeException();
}

JsonArray jsonArray = element.getAsJsonArray();

Heck, use List interface to collect values before converting it JSON Tree.

edited May 28, 2020 at 6:09

answered Sep 17, 2013 at 19:12

Ahsan Mahboob Shah

4,0392 gold badges37 silver badges50 bronze badges

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

Comments

KPrince36 · Accepted Answer · 2016-07-13 21:52:51Z

14

As an additional answer, it can also be made shorter.

List<Customer> customerList = CustomerDB.selectAll();

JsonArray result = (JsonArray) new Gson().toJsonTree(customerList,
            new TypeToken<List<Customer>>() {
            }.getType());

edited Jul 13, 2016 at 21:52

KPrince36

2,9462 gold badges23 silver badges30 bronze badges

answered Sep 22, 2015 at 10:57

Fadils

1,52617 silver badges21 bronze badges

Comments

Danjoa · Accepted Answer · 2016-12-29 13:16:51Z

6

Don't know how well this solution performs compared to the other answers but this is another way of doing it, which is quite clean and should be enough for most cases.

ArrayList<Customer> customerList = CustomerDB.selectAll();
Gson gson = new Gson();
String data = gson.toJson(customerList);
JsonArray jsonArray = new JsonParser().parse(data).getAsJsonArray();

Would love to hear from someone else though if, and then how, inefficient this actually is.

answered Dec 29, 2016 at 13:16

Danjoa

1534 silver badges14 bronze badges

1 Comment

momvart Over a year ago

At first step you are serializing the list to string and then you deserialize the string. So it is really inefficient.

Hitesh Sahu · Accepted Answer · 2017-12-25 13:49:45Z

3

Consider a list of Objects of type `Model.class`

ArrayList<Model> listOfObjects = new ArrayList<Model>();

List to JSON

String jsonText =  new Gson().toJson(listOfObjects);

JSON to LIST

 Type listType = new TypeToken<List<Model>>() {}.getType();

 List<Model> myModelList = new Gson().fromJson(jsonText , listType);

answered Dec 25, 2017 at 13:49

Hitesh Sahu

45.6k18 gold badges217 silver badges160 bronze badges

Comments

TapanHP · Accepted Answer · 2018-07-08 03:40:42Z

3

For Anyone who is doing it in Kotlin, you can get it this way,

val gsonHandler = Gson()
val element: JsonElement = gsonHandler.toJsonTree(yourListOfObjects, object : TypeToken<List<YourModelClass>>() {}.type)

edited Jul 8, 2018 at 3:40

answered Feb 3, 2018 at 4:52

TapanHP

6,2317 gold badges41 silver badges68 bronze badges

Comments

cdkrot · Accepted Answer · 2013-09-17 19:14:20Z

1

List<> is a normal java object, and can be successfully transformed using standard gson object api. List in gson looks like this:

"libraries": [
    {
      //Containing object 
    },
    {
      //Containing object 
    }
   ],
...

answered Sep 17, 2013 at 19:14

cdkrot

2791 gold badge2 silver badges8 bronze badges

Collectives™ on Stack Overflow

How to convert ArrayList of custom class to JsonArray in Java?

6 Answers 6

Comments

Comments

1 Comment

Consider a list of Objects of type `Model.class`

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

Comments

1 Comment

Consider a list of Objects of type Model.class

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related

Consider a list of Objects of type `Model.class`