Java - Duda: Como convertir string en jsonArray

URL url2 = new URL(url);

            HttpURLConnection conn = (HttpURLConnection) url2.openConnection();

            conn.setRequestMethod("GET");

            conn.setRequestProperty("Content-Type", "application/json; charset=UTF-8");

            BufferedReader br = new BufferedReader(new InputStreamReader((conn.getInputStream())));

 String output;

        System.out.println("Output from Server .... \n");

        while ((output = br.readLine()) != null) {

            System.out.println(output);

        }

        JSONObject jObject = new JSONObject();

JSONArray jArray = jObject.getJSONArray(output);

for (int i = 0; i < jArray.length(); i++) {

        JSONObject jObj = jArray.getJSONObject(i);

        System.out.println(i + " id : " + jObj.getInt("idLibro"));

}

import org.json.simple.JSONObject;

import org.json.simple.JSONArray;

import org.json.simple.parser.ParseException;

import org.json.simple.parser.JSONParser;

class JsonDecodeDemo

{

   public static void main(String[] args)

   {

      JSONParser parser=new JSONParser();

      String s = "[0,{\"1\":{\"2\":{\"3\":{\"4\":[5,{\"6\":7}]}}}}]";

      try{

         Object obj = parser.parse(s);

         JSONArray array = (JSONArray)obj;

         System.out.println("El segundo elemento del array");

         System.out.println(array.get(1));

         System.out.println();

         JSONObject obj2 = (JSONObject)array.get(1);

         System.out.println("Campo \"1\"");

         System.out.println(obj2.get("1"));

         s = "{}";

         obj = parser.parse(s);

         System.out.println(obj);

         s= "[5,]";

         obj = parser.parse(s);

         System.out.println("5ta posición: " + obj);

         s= "[5,,2]";

         obj = parser.parse(s);

         System.out.println(obj);

      }catch(ParseException pe){

         System.out.println("position: " + pe.getPosition());

         System.out.println(pe);

      }

   }

}

El segundo elemento del array

{"1":{"2":{"3":{"4":[5,{"6":7}]}}}}

Campo "1"

{"2":{"3":{"4":[5,{"6":7}]}}}

{}

5ta posición: [5]

[5,2]

import org.json.*;

public class JsonArray {

    public static void main(String [] args) {

        String output = "[{\"idLibro\":1,\"nombre\":\"Luces de sept\"},{\"idLibro\":2,\"nombre\":\"Luces de oct\"}]";

        JSONArray jArray = new JSONArray(output);

        for (int i = 0; i < jArray.length(); i++) {

            JSONObject jObj = jArray.getJSONObject(i);

            System.out.println(i + " id : " + jObj.getInt("idLibro"));

        }

    }

}