working solution

JSONParser parser = new JSONParser();
JSONObject jsonObject;
try {

    jsonObject = (JSONObject) parser.parse(new FileReader("E:\\json.txt"));

    out.println("<br>"+jsonObject);


    JSONArray from_excel = (JSONArray)jsonObject.get("from_excel");
    // for row output 1
    for(Object o: from_excel){
        out.println("<br>"+o);
    }
    // for row output 2
    Iterator iterator = from_excel.iterator();
    while (iterator.hasNext()) {
        out.println("<br>"+iterator.next());
    }
    // for item output 3
    for (int i = 0; i < from_excel.size(); i++) {

        JSONObject jsonObjectRow = (JSONObject) from_excel.get(i);
        String num = (String) jsonObjectRow.get("num");
        String solution = (String) jsonObjectRow.get("solution");
        out.println("<br>num="+num+"; solution="+solution);
    }
} catch (Exception e) {
    out.println("Error: "+e);
}

Use this for get json value in string format from file

public String loadJSONFromFile() {
    String json = null;
    try {
        InputStream is = getActivity().getAssets().open("yourfilename.json");
        int size = is.available();
        byte[] buffer = new byte[size];
        is.read(buffer);
        is.close();
        json = new String(buffer, "UTF-8");
    } catch (IOException ex) {
        ex.printStackTrace();
        return null;
    }
    return json;
}

JsonObject is a child of a JsonArray, so as per my suggestion use like this

final JSONArray jsonArray = new JSONArray();
jsonArray.put(obj); //obj is your JsonObject 

and you can get JsonObject from array like

jsonArray.getJSONObject(0); //0 is index of your JsonObject in JsonArray

Hope this help you.

The whole file is an array and there are objects and other arrays (e.g. cars) in the whole array of the file.

As you say, the outermost layer of your JSON blob is an array. Therefore, your parser will return a JSONArray. You can then get JSONObjects from the array ...

  JSONArray a = (JSONArray) parser.parse(new FileReader("c:\\exer4-courses.json"));

  for (Object o : a)
  {
    JSONObject person = (JSONObject) o;

    String name = (String) person.get("name");
    System.out.println(name);

    String city = (String) person.get("city");
    System.out.println(city);

    String job = (String) person.get("job");
    System.out.println(job);

    JSONArray cars = (JSONArray) person.get("cars");

    for (Object c : cars)
    {
      System.out.println(c+"");
    }
  }

For reference, see "Example 1" on the json-simple decoding example page.

1. Create a POJO class to represent your JSON data:

   public class CarInfo {  
     String car;
     String colour;
     String qty;
     String date_manufactured; 
   }
   

2. Use GSON to parse JSON String Array

   String carInfoJson = "[{ \"car\": \"Toyota\", \"colour\": \"red\",\"qty\": \"1\",\"date_manufactured\":\"12972632260006\" }, { \"car\":\"Hyundai\", \"colour\":\"red\",\"qty\":\"2\",\"date_manufactured\":\"1360421626000\" }]";
   Gson gson = new Gson();  
   CarInfo[] carInfoArray = gson.fromJson(carInfoJson, CarInfo[].class);  
   

3. Use GSON to parse JSON String Array from a file

   String carInfoJson= new String(Files.readAllBytes(Paths.get("filename.txt")));
   Gson gson = new Gson();  
   CarInfo[] carInfoArray = gson.fromJson(carInfoJson, CarInfo[].class);
   

4. Use GSON to parse JSON String Array from a file using BufferedReader

   BufferedReader reader = null;
   try {
     reader = new BufferedReader(new FileReader(file));
     Gson gson = new Gson(); 
     CarInfo[] carInfoArray = gson.fromJson(reader, CarInfo[].class);
   } catch (FileNotFoundException ex) {
     ...
   } finally {
     ...
   }
   

5. Use GSON to parse JSON String Array from a file using JsonReader in stream mode

   try {
     InputStream stream = new FileInputStream("c:\\filename.txt");
     JsonReader reader = new JsonReader(new InputStreamReader(stream, "UTF-8"));
     Gson gson = new Gson();
   
     // Read file in stream mode
     reader.beginArray();
     while (reader.hasNext()) {
       CarInfo carInfo = gson.fromJson(reader, CarInfo.class);
     }
     reader.endArray();
     reader.close();
   } catch (UnsupportedEncodingException ex) {
     ...
   } catch (IOException ex) {
     ...
   }
   

You can use gson library

You can use Maven or jar file: http://mvnrepository.com/artifact/com.google.code.gson/gson

package com.test;

import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class AppJsonTest {

    public static void main(String[] args) {
        List<DataObject> objList = new ArrayList<DataObject>();
        objList.add(new DataObject(1, "Coca Cola", 0.9, 19));
        objList.add(new DataObject(2, "Coca Cola Zero", 0.6, 19));

        // Convert the object to a JSON string
        String json = new Gson().toJson(objList);
        System.out.println(json);

        // Now convert the JSON string back to your java object
        Type type = new TypeToken<List<DataObject>>() {
        }.getType();
        List<DataObject> inpList = new Gson().fromJson(json, type);
        for (int i = 0; i < inpList.size(); i++) {
            DataObject x = inpList.get(i);
            System.out.println(x.toString());
        }
    }
}

class DataObject {
    int idProducto;
    String Nombre;
    Double Precio;
    int Cantidad;

    public DataObject(int idProducto, String nombre, Double precio, int cantidad) {
        this.idProducto = idProducto;
        Nombre = nombre;
        Precio = precio;
        Cantidad = cantidad;
    }

    public int getIdProducto() {
        return idProducto;
    }

    public void setIdProducto(int idProducto) {
        this.idProducto = idProducto;
    }

    public String getNombre() {
        return Nombre;
    }

    public void setNombre(String nombre) {
        Nombre = nombre;
    }

    public Double getPrecio() {
        return Precio;
    }

    public void setPrecio(Double precio) {
        Precio = precio;
    }

    public int getCantidad() {
        return Cantidad;
    }

    public void setCantidad(int cantidad) {
        Cantidad = cantidad;
    }

    @Override
    public String toString() {
        return "DataObject [idProducto=" + idProducto + ", Nombre=" + Nombre + ", Precio=" + Precio + ", Cantidad=" + Cantidad + "]";
    }

}

You could use this library:

http://www.json.org/java/

Then you can read the file into a String used a BufferedReader, close the reader and do something like this:

JSONArray ja = new JSONOArray(string);
int[][] result = new int[ja.length()][];
for (int i = 0; i < ja.length(); i++) {
    JSONAarray ja2 = ja.getJSONArray(i);
    result[i] = new int[ja2.length()];
    for (int j = 0; j < ja2.length(); j++) {
        result[i][j]=ja2.getInt(j);
    }
}

I haven't tested this code, and you also might want to add some error checking and extract local variables, depending on how sure you are the file is in the right format. This does not assume your file contains a rectangular matrix.