Java ArrayList of hasMap to return in Spring endpoint

I have some sample objects that will be included in an ArrayList, and these items must appear in the specific format, the problem that each item must be is a new position of an array in the json return.

follow the code I have developed so far:

import java.util.List;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
public class MyClass {
String text = "hi";
String language = "pt-br";
String item = "1";
public static void main(String args[]) {
MyClass myObj1 = new MyClass();
myObj1.text = "ola";
myObj1.language = "pt-br";
myObj1.item = "1";
MyClass myObj2 = new MyClass();
myObj2.text = "hi";
myObj2.language = "en";
myObj2.item = "1";
MyClass myObj3 = new MyClass();
myObj3.text = "holaa";
myObj3.language = "es";
myObj3.item = "2";
MyClass myObj4 = new MyClass();
myObj4.text = "olaaaaa";
myObj4.language = "pt-br";
myObj4.item = "2";
MyClass myObj5 = new MyClass();
myObj5.text = "helllooo";
myObj5.language = "eng";
myObj5.item = "3";
List<MyClass> lang = new ArrayList<MyClass>();
lang.add(myObj1);
lang.add(myObj2);
lang.add(myObj3);
lang.add(myObj3);
lang.add(myObj4);
ArrayList<HashMap<String, String>> lista = new ArrayList<>();
HashMap<String, String> mapa = new HashMap<>();
for(int i = 0; i < lang.size();i++) {
if(i > 0 && lang.get(i).item != lang.get(i-1).item) {
lista.add(mapa);
mapa.clear();
}
if(i == lang.size()-1){
lista.add(mapa);
mapa.clear();
}
mapa.put(lang.get(i).language, lang.get(i).text); 
}
System.out.println(lista.toString());
}
}

which should be returned in this pattern:

[{
"item_id": 1,
"language": [{
"pt-br": "ola",
"en": "hii"
}]
}, {
"item_id": 2,
"language": [{
"es": "holaa",
"pt-br": "olaaaaa"
}]
}, {
"item_id": 3,
"language": [{
"eng": "helllooo"
}]
}]

the whole part of Spring is already implemented, I need to manipulate the result so that it is displayed correctly in my endpoint.

It is worth to implement an Item object and then transform the input List<MyClass> lang into List<Item>:

@JsonNaming(PropertyNamingStrategy.SnakeCaseStrategy.class)
public class Item {
    int item_id;
    List<Map<String, String>> language; // perhaps Map<String, String> would do fine

    Item(Map.Entry<Integer, Map<String, String>> entry) {
        this(entry.getKey(), entry.getValue());
    }
    
    Item(int id, Map<String, String> language) {
        this.item_id = id;
        this.language = Arrays.asList(language);
    }
    
    public String toString() {
        return String.format("item_id: %d,%nlanguage: %s%n", item_id, language);
    }
    // getters/setters
}

// MyClass.java
static List<Item> transform(List<MyClass> data) {
    return data
            .stream()
            .collect(Collectors.groupingBy(
                x -> Integer.parseInt(x.item), // to become int `item_id`
                LinkedHashMap::new,            // keep insertion order 
                Collectors.mapping(            // prepare map language:text
                    x -> Map.entry(x.language, x.text),  // Java 9
                    Collectors.toMap(
                        Map.Entry::getKey, 
                        Map.Entry::getValue, 
                        (a, b) -> a,           // merge occasional duplicates
                        LinkedHashMap::new)    // keep insertion order or TreeMap to sort by language
                    )
            ))
            .entrySet().stream()
            .map(Item::new)  // referencing overloaded constructor
            .collect(Collectors.toList());
}

Test

List<Item> items = transform(lang);
items.forEach(System.out::println);

Output

item_id: 1,
language: [{pt-br=ola, en=hi}]
item_id: 2,
language: [{es=holaa, pt-br=olaaaaa}]
item_id: 3,
language: [{eng=helllooo}]

Comments:

• if Java 9 Map.entry cannot be used, it may be replaced with older new AbstractMap.SimpleEntry(x.language, x.text)
• not sure whether list of maps is really needed in Item, it is provided just to meet the requirement as well as Arrays.asList(e.getValue()); the map instance should be fine.
• in Item class use Jackson SnakeCaseStrategy in @JsonNaming annotation to guarantee proper serialization of item_id.

Update<br/>
Fixed and added an overloaded constructor in Item class, used method reference Item::new in transform