Reformat JSON arrays/object in java

Assign the JSON to String variable, for example assign the above JSON to variable called json:

String json = "..." // here put your JSON text;

Prepare classes for your objects:

class Fruit {
    private String name;
    private boolean organic;
}

class Fruits {
    private List<Fruit> fruits;
}

then use Gson to convert JSON to your objects:

Gson gson = new Gson();
Fruits fruits = gson.fromJson(json, Fruits.class);

Next prepare wrapper class ListOfFruits for your fruits object:

class ListOfFruits {
    private Fruits listOfFruits;

    public ListOfFruits(Fruits fruits) {
        listOfFruits = fruits;
    }
}

Next pack your fruits object into another one:

ListOfFruits lof = new ListOfFruits(fruits);

And finally generate back the output JSON:

String newJson = gson.toJson(lof);

You do not need to create POJO model for reading and updating JSON. Using Jackson, you can read whole JSON payload to JsonNode, create a Map with required key and serialising to JSON back. See below example:

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.io.File;
import java.util.Collections;
import java.util.Map;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);

        JsonNode root = mapper.readTree(jsonFile);
        Map<String, JsonNode> output = Collections.singletonMap("List Fruits", root);

        System.out.println(mapper.writeValueAsString(output));
    }
}

Above code prints:

{
  "List Fruits" : {
    "Fruits" : [ {
      "name" : "avocado",
      "organic" : true
    }, {
      "name" : "mango",
      "organic" : true
    } ]
  }
}

I would highly recommend going through the documentations of Jackson or Gson libraries as you mentioned you are new. I have created a sample git repo for this item. This sample uses Jackson API.

Visit https://github.com/rajramo61/jsonwrapper

final InputStream fileData = ClassLoader.getSystemResourceAsStream("file.json");
    ObjectMapper mapper = new ObjectMapper();
    InitialJson initialJson = mapper.readValue(fileData, InitialJson.class);
    System.out.println(mapper.writeValueAsString(initialJson));
    final FinalJson finalJson = new FinalJson();
    finalJson.setListOfFruits(initialJson);
    System.out.println(mapper.writeValueAsString(finalJson));

This is the Fruit class.

public class Fruit {
private String name;
private boolean organic;

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public boolean getOrganic() {
    return organic;
}

public void setOrganic(boolean organic) {
    this.organic = organic;
}

@Override
public String toString() {
    return "Fruit{" +
            "name='" + name + '\'' +
            ", organic=" + organic +
            '}';
}

}

Here is FinalJson class detail. This is the class will wrap the initial json loaded from jsn file.

public class FinalJson {
private InitialJson listOfFruits;

@JsonProperty("List Fruits")
public InitialJson getListOfFruits() {
    return listOfFruits;
}

public void setListOfFruits(InitialJson listOfFruits) {
    this.listOfFruits = listOfFruits;
}

}

Here is InitialJson class detail. This is the class pulls data from json file.

public class InitialJson {
private List<Fruit> fruits;

@JsonProperty("Fruits")
public List<Fruit> getFruits() {
    return fruits;
}

public void setFruits(List<Fruit> fruits) {
    this.fruits = fruits;
}

@Override
public String toString() {
    return "InitialJson{" +
            "fruits=" + fruits +
            '}';
}

}

You can fork the repo and close this in local and it should work fine.