Build Complex JSON payload from java classes

Question

I would like to create following json payload from the java classes. Only one condition is there, Subgroup1 can be null, meaning group may/may not have subgroup1. Not sure how can it be done. Any help would be highly appreciated. Thanks in advance! I can change the classes if needed.

{
    "data" : [
            {
              "id": "1",
              "name": "ab",
              "children": [
                        {
                          "id": "1",
                          "name": "xyz",
                          "children": [
                                                { "id": "1",
                                                 "name": "opl"
                                                } ] 
                        }
                ]
            },
            {
              "id":" 2",
              "name": "cd",
              "children": [
                    {
                      "id": "1",
                      "name": "ijk",
                      "children": [
                                    { "id": "1",
                                      "name": "rty"},
                                        { "id": "2",
                                          "name": "wsc"
                                        } ]
                    },
                    {
                      "id": "2",
                      "name": "lmn",
                      "children": [
                                        { "id": "1",
                                          "name": "qaz"},
                                        { "id": "2",
                                          "name": "poi"
                                        } ]
                    },
                    {
                      "id": "3",
                      "name": "opq",
                      "children": [
                                        { "id": "1",
                                          "name": "edf"},
                                        { "id": "2",
                                          "name": "bhgga"
                                        } ]
                    }
              ]
            },
            {
              "id": "3",
              "name": "ef",
              "children": [
                      { 
                        "id": null,
                        "name": null,
                        "children": [
                                            { "id": "2",
                                              "name": "ijyuht"
                                        } ]
                        }
                    ]
            }
        ]
  }

I have 3 different java classes to map objects.

Data.class

public class Data {

    private Long id;
    private String name;
    private List<Subgroup1> children;
}

Subgroup1.class

public class Subgroup1 {

    private Long id;
    private String name;
    private List<Subgroup2> children;
}

Subgroup2.class

public class Subgroup2 {

    private Long id;
    private String name;

}

Answer 1

Create Classes structure as below:

public class MainClass {

private List<Datum> data;

}


public class Datum {

private List<Child> children;
private String id;
private String name;

}

public class Child {

private List<Child> children;
private String id;
private String name;

}

below format you can use in Java, its just a way you can do it in multiples way, as i have expained in a easy way.

    MainClass mainClass = new MainClass();
    
    List<Child> level2List = new ArrayList<>();
    Child level2Child = new Child();
    level2Child.setName("opl");
    level2Child.setId("1");
    level2List.add(level2Child);


    List<Child> childList = new ArrayList<>();
    Child child = new Child();
    child.setChildren(level2List);
    child.setId("1");
    child.setName("xyz");
    childList.add(child);


    Datum datum = new Datum();
    datum.setChildren(childList);
    datum.setId("1");
    datum.setName("ab");

    List<Datum> datumList = new ArrayList<>();
    datumList.add(datum);
    mainClass.setData(datumList);
    System.out.println(new Gson().toJson(mainClass));