How to convert List to a JSON Object using GSON?

Question

I have a List which I need to convert into JSON Object using GSON. My JSON Object has JSON Array in it.

public class DataResponse {

    private List<ClientResponse> apps;

    // getters and setters

    public static class ClientResponse {
        private double mean;
        private double deviation;
        private int code;
        private String pack;
        private int version;

        // getters and setters
    }
}

Below is my code in which I need to convert my List to JSON Object which has JSON Array in it -

public void marshal(Object response) {

    List<DataResponse.ClientResponse> clientResponse = ((DataResponse) response).getClientResponse();

    // now how do I convert clientResponse list to JSON Object which has JSON Array in it using GSON?

    // String jsonObject = ??
}

As of now, I only have two items in List - So I need my JSON Object like this -

{  
   "apps":[  
      {  
         "mean":1.2,
         "deviation":1.3
         "code":100,
         "pack":"hello",
         "version":1
      },
      {  
         "mean":1.5,
         "deviation":1.1
         "code":200,
         "pack":"world",
         "version":2
      }
   ]
}

What is the best way to do this?

Answer 1

There is a sample from google gson documentation on how to actually convert the list to json string:

Type listType = new TypeToken<List<String>>() {}.getType();
 List<String> target = new LinkedList<String>();
 target.add("blah");

 Gson gson = new Gson();
 String json = gson.toJson(target, listType);
 List<String> target2 = gson.fromJson(json, listType);

You need to set the type of list in toJson method and pass the list object to convert it to json string or vice versa.

Answer 2

If response in your marshal method is a DataResponse , then that's what you should be serializing.

Gson gson = new Gson();
gson.toJson(response);

That will give you the JSON output you are looking for.

Answer 3

Assuming you also want to get json in format

{
  "apps": [
    {
      "mean": 1.2,
      "deviation": 1.3,
      "code": 100,
      "pack": "hello",
      "version": 1
    },
    {
      "mean": 1.5,
      "deviation": 1.1,
      "code": 200,
      "pack": "world",
      "version": 2
    }
  ]
}

instead of

{"apps":[{"mean":1.2,"deviation":1.3,"code":100,"pack":"hello","version":1},{"mean":1.5,"deviation":1.1,"code":200,"pack":"world","version":2}]}

you can use pretty printing . To do so use

Gson gson = new GsonBuilder().setPrettyPrinting().create();
String json = gson.toJson(dataResponse);

Answer 4

确保将您的集合转换为数组：

Gson().toJson(objectsList.toTypedArray(), Array<CustomObject>::class.java)

Answer 5

We can also use another workaround by first creating an array of myObject then convert them into list.

final Optional<List<MyObject>> sortInput = Optional.ofNullable(jsonArgument)
                .map(jsonArgument -> GSON.toJson(jsonArgument, ArrayList.class))
                .map(gson -> GSON.fromJson(gson, MyObject[].class))
                .map(myObjectArray -> Arrays.asList(myObjectArray));

Benifits:

• we are not using reflection here. :)