Android Java; ¿Cómo puedo analizar un archivo JSON local de la carpeta de activos en un ListView?

Actualmente estoy desarrollando una aplicación de física que se supone que muestra una lista de fórmulas e incluso resuelve algunas de ellas (el único problema es el ListView)

Este es mi diseño principal

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:measureWithLargestChild="false"
    android:orientation="vertical"
    tools:context=".CatList" >


    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@drawable/titlebar" >

        <TextView
            android:id="@+id/Title1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_centerVertical="true"
            android:text="@string/app_name"
            android:textAppearance="?android:attr/textAppearanceLarge"
            android:textColor="#ff1c00"
            android:textIsSelectable="false" />

    </RelativeLayout>

    <ListView
        android:id="@+id/listFormulas"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

    </ListView>

</LinearLayout>

Y esta es mi actividad principal.

package com.wildsushii.quickphysics;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONException;
import org.json.JSONObject;

import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.content.res.AssetManager;
import android.view.Menu;
import android.widget.ListView;

public class CatList extends Activity {



    public static String AssetJSONFile (String filename, Context context) throws IOException {
        AssetManager manager = context.getAssets();
        InputStream file = manager.open(filename);
        byte[] formArray = new byte[file.available()];
        file.read(formArray);
        file.close();

        return new String(formArray);
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cat_list);
        ListView categoriesL = (ListView)findViewById(R.id.listFormulas);

        ArrayList<HashMap<String, String>> formList = new ArrayList<HashMap<String, String>>();
        Context context = null;
        try {
            String jsonLocation = AssetJSONFile("formules.json", context);
            JSONObject formArray = (new JSONObject()).getJSONObject("formules");
            String formule = formArray.getString("formule");
            String url = formArray.getString("url");
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }

        //My problem is here!!
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.cat_list, menu);
        return true;
    }
}

De hecho, sé que puedo hacer esto sin usar JSON, pero necesito más práctica para analizar JSON. Por cierto, este es el JSON

    {
    "formules": [
    {
      "formule": "Linear Motion",
      "url": "qp1"
    },
    {
      "formule": "Constant Acceleration Motion",
      "url": "qp2"
    },
    {
      "formule": "Projectile Motion",
      "url": "qp3"
    },
    {
      "formule": "Force",
      "url": "qp4"
    },
    {
      "formule": "Work, Power, Energy",
      "url": "qp5"
    },
    {
      "formule": "Rotary Motion",
      "url": "qp6"
    },
    {
      "formule": "Harmonic Motion",
      "url": "qp7"
    },
    {
      "formule": "Gravity",
      "url": "qp8"
    },
    {
      "formule": "Lateral and Longitudinal Waves",
      "url": "qp9"
    },
    {
      "formule": "Sound Waves",
      "url": "qp10"
    },
    {
      "formule": "Electrostatics",
      "url": "qp11"
    },
    {
      "formule": "Direct Current",
      "url": "qp12"
    },
    {
      "formule": "Magnetic Field",
      "url": "qp13"
    },
    {
      "formule": "Alternating Current",
      "url": "qp14"
    },
    {
      "formule": "Thermodynamics",
      "url": "qp15"
    },
    {
      "formule": "Hydrogen Atom",
      "url": "qp16"
    },
    {
      "formule": "Optics",
      "url": "qp17"
    },
    {
      "formule": "Modern Physics",
      "url": "qp18"
    },
    {
      "formule": "Hydrostatics",
      "url": "qp19"
    },
    {
      "formule": "Astronomy",
      "url": "qp20"
    }
  ]
}

He intentado muchas cosas e incluso elimino todo el proyecto para crear uno nuevo :(

Como Faizan describe en su respuesta aquí :

En primer lugar, lea el archivo Json de su archivo de evaluaciones utilizando el código a continuación.

y luego simplemente puede leer este retorno de cadena por esta función como

public String loadJSONFromAsset() {
    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;
}

y usar este método así

    try {
        JSONObject obj = new JSONObject(loadJSONFromAsset());
        JSONArray m_jArry = obj.getJSONArray("formules");
        ArrayList<HashMap<String, String>> formList = new ArrayList<HashMap<String, String>>();
        HashMap<String, String> m_li;

        for (int i = 0; i < m_jArry.length(); i++) {
            JSONObject jo_inside = m_jArry.getJSONObject(i);
            Log.d("Details-->", jo_inside.getString("formule"));
            String formula_value = jo_inside.getString("formule");
            String url_value = jo_inside.getString("url");

            //Add your values in your `ArrayList` as below:
            m_li = new HashMap<String, String>();
            m_li.put("formule", formula_value);
            m_li.put("url", url_value);

            formList.add(m_li);
        }
    } catch (JSONException e) {
        e.printStackTrace();
    }

Para más detalles sobre JSON, lea AQUÍ

{ // json object node
    "formules": [ // json array formules
    { // json object 
      "formule": "Linear Motion", // string
      "url": "qp1"
    }

Qué estás haciendo

  Context context = null; // context is null 
    try {
        String jsonLocation = AssetJSONFile("formules.json", context);

Entonces cambia a

   try {
        String jsonLocation = AssetJSONFile("formules.json", CatList.this);

Analizar

Creo que obtienes la cadena de la carpeta de evaluaciones.

try
{
String jsonLocation = AssetJSONFile("formules.json", context);
JSONObject jsonobject = new JSONObject(jsonLocation);
JSONArray jarray = (JSONArray) jsonobject.getJSONArray("formules");
for(int i=0;i<jarray.length();i++)
{
JSONObject jb =(JSONObject) jarray.get(i);
String formula = jb.getString("formule");
String url = jb.getString("url");
}
} catch (IOException e) {
        e.printStackTrace();
} catch (JSONException e) {
        e.printStackTrace();
}

Con Kotlin tiene esta función de extensión para leer el archivo devuelto como cadena.

fun AssetManager.readAssetsFile(fileName : String): String = open(fileName).bufferedReader().use{it.readText()}

Analiza la cadena de salida usando cualquier analizador JSON.

Método para leer el archivo JSON de la carpeta Assets y devolverlo como un objeto de cadena.

public static String getAssetJsonData(Context context) {
            String json = null;
            try {
                InputStream is = context.getAssets().open("myJson.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;
            }

            Log.e("data", json);
            return json;

        }

Ahora para analizar datos en su actividad: -

String data = getAssetJsonData(getApplicationContext());
        Type type = new TypeToken<Your Data model>() {
        }.getType();
  <Your Data model> modelObject = new Gson().fromJson(data, type);

Código fuente Cómo obtener Json local de la carpeta Activos

https://drive.google.com/open?id=1NG1amTVWPNViim_caBr8eeB4zczTDK2p

    {
        "responseCode": "200",
        "responseMessage": "Recode Fetch Successfully!",
        "responseTime": "10:22",
        "employeesList": [
            {
                "empId": "1",
                "empName": "Keshav",
                "empFatherName": "Mr Ramesh Chand Gera",
                "empSalary": "9654267338",
                "empDesignation": "Sr. Java Developer",
                "leaveBalance": "3",
                "pfBalance": "60,000",
                "pfAccountNo.": "12345678"
            },
            {
                "empId": "2",
                "empName": "Ram",
                "empFatherName": "Mr Dasrath ji",
                "empSalary": "9999999999",
                "empDesignation": "Sr. Java Developer",
                "leaveBalance": "3",
                "pfBalance": "60,000",
                "pfAccountNo.": "12345678"
            },
            {
                "empId": "3",
                "empName": "Manisha",
                "empFatherName": "Mr Ramesh Chand Gera",
                "empSalary": "8826420999",
                "empDesignation": "BusinessMan",
                "leaveBalance": "3",
                "pfBalance": "60,000",
                "pfAccountNo.": "12345678"
            },
            {
                "empId": "4",
                "empName": "Happy",
                "empFatherName": "Mr Ramesh Chand Gera",
                "empSalary": "9582401701",
                "empDesignation": "Two Wheeler",
                "leaveBalance": "3",
                "pfBalance": "60,000",
                "pfAccountNo.": "12345678"
            },
            {
                "empId": "5",
                "empName": "Ritu",
                "empFatherName": "Mr Keshav Gera",
                "empSalary": "8888888888",
                "empDesignation": "Sararat Vibhag",
                "leaveBalance": "3",
                "pfBalance": "60,000",
                "pfAccountNo.": "12345678"
            }
        ]
    }


 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_employee);


        emp_recycler_view = (RecyclerView) findViewById(R.id.emp_recycler_view);

        emp_recycler_view.setLayoutManager(new LinearLayoutManager(EmployeeActivity.this, 
        LinearLayoutManager.VERTICAL, false));
        emp_recycler_view.setItemAnimator(new DefaultItemAnimator());

        employeeAdapter = new EmployeeAdapter(EmployeeActivity.this , employeeModelArrayList);

        emp_recycler_view.setAdapter(employeeAdapter);

        getJsonFileFromLocally();
    }



    public String loadJSONFromAsset() {
        String json = null;
        try {
            InputStream is = EmployeeActivity.this.getAssets().open("employees.json");       //TODO Json File  name from assets folder
            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;
    }

    private void getJsonFileFromLocally() {
        try {

            JSONObject jsonObject = new JSONObject(loadJSONFromAsset());
            String responseCode = jsonObject.getString("responseCode");
            String responseMessage = jsonObject.getString("responseMessage");
            String responseTime = jsonObject.getString("responseTime");

            Log.e("keshav", "responseCode -->" + responseCode);
            Log.e("keshav", "responseMessage -->" + responseMessage);
            Log.e("keshav", "responseTime -->" + responseTime);


            if(responseCode.equals("200")){

            }else{
                Toast.makeText(this, "No Receord Found ", Toast.LENGTH_SHORT).show();
            }

            JSONArray jsonArray = jsonObject.getJSONArray("employeesList");                  //TODO pass array object name
            Log.e("keshav", "m_jArry -->" + jsonArray.length());


            for (int i = 0; i < jsonArray.length(); i++)
            {
                EmployeeModel employeeModel = new EmployeeModel();

                JSONObject jsonObjectEmployee = jsonArray.getJSONObject(i);


                String empId = jsonObjectEmployee.getString("empId");
                String empName = jsonObjectEmployee.getString("empName");
                String empDesignation = jsonObjectEmployee.getString("empDesignation");
                String empSalary = jsonObjectEmployee.getString("empSalary");
                String empFatherName = jsonObjectEmployee.getString("empFatherName");

                employeeModel.setEmpId(""+empId);
                employeeModel.setEmpName(""+empName);
                employeeModel.setEmpDesignation(""+empDesignation);
                employeeModel.setEmpSalary(""+empSalary);
                employeeModel.setEmpFatherNamer(""+empFatherName);

                employeeModelArrayList.add(employeeModel);

            }       // for

            if(employeeModelArrayList!=null) {
                employeeAdapter.dataChanged(employeeModelArrayList);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

Usando OKIO

public static String readFileFromAssets(Context context, String fileName) {

            try {
                InputStream input = context.getAssets().open(fileName);
                BufferedSource source = Okio.buffer(Okio.source(input));
                return source.readByteString().string(Charset.forName("utf-8"));
            } catch (IOException e) {
                e.printStackTrace();
            }

            return null;
    }

y entonces...

String data = readFileFromAssets(context, "json/some.json"); //here is my file inside the folder assets/json/some.json
        Type reviewType = new TypeToken<List<Object>>() {
}.getType();
Object object = new Gson().fromJson(data, reviewType);

Simplemente resumiendo la respuesta de @ libing con una muestra que funcionó para mí.

val gson = Gson()
val todoItem: TodoItem = gson.fromJson(this.assets.readAssetsFile("versus.json"), TodoItem::class.java)

private fun AssetManager.readAssetsFile(fileName : String): String = open(fileName).bufferedReader().use{it.readText()}

Sin esta función de extensión, se puede lograr lo mismo usando BufferedReadery de InputStreamReaderesta manera:

val i: InputStream = this.assets.open("versus.json")
val br = BufferedReader(InputStreamReader(i))
val todoItem: TodoItem = gson.fromJson(br, TodoItem::class.java)

Si está utilizando Kotlin en Android, puede crear la función de extensión .
Las funciones de extensión se definen fuera de cualquier clase; sin embargo, hacen referencia al nombre de la clase y pueden usarse this. En nuestro caso usamos applicationContext.
Entonces, en la clase de utilidad, puede definir todas las funciones de extensión.

Utility.kt

fun Context.loadJSONFromAssets(fileName: String): String {
    return applicationContext.assets.open(fileName).bufferedReader().use { reader ->
        reader.readText()
    }
}

MainActivity.kt

Puede definir una función privada para cargar datos JSON desde una afirmación como esta:

 lateinit var facilityModelList: ArrayList<FacilityModel>
 private fun bindJSONDataInFacilityList() {
    facilityModelList = ArrayList<FacilityModel>()
    val facilityJsonArray = JSONArray(loadJSONFromAsserts("NDoH_facility_list.json")) // Extension Function call here
    for (i in 0 until facilityJsonArray.length()){
        val facilityModel = FacilityModel()
        val facilityJSONObject = facilityJsonArray.getJSONObject(i)
        facilityModel.Facility = facilityJSONObject.getString("Facility")
        facilityModel.District = facilityJSONObject.getString("District")
        facilityModel.Province = facilityJSONObject.getString("Province")
        facilityModel.Subdistrict = facilityJSONObject.getString("Facility")
        facilityModel.code = facilityJSONObject.getInt("code")
        facilityModel.gps_latitude = facilityJSONObject.getDouble("gps_latitude")
        facilityModel.gps_longitude = facilityJSONObject.getDouble("gps_longitude")

        facilityModelList.add(facilityModel)
    }
}

Tienes que pasar facilityModelListtuListView

FacilityModel.kt

class FacilityModel: Serializable {
    var District: String = ""
    var Facility: String = ""
    var Province: String = ""
    var Subdistrict: String = ""
    var code: Int = 0
    var gps_latitude: Double= 0.0
    var gps_longitude: Double= 0.0
}

En mi caso, la respuesta JSON comienza con JSONArray

[
  {
    "code": 875933,
    "Province": "Eastern Cape",
    "District": "Amathole DM",
    "Subdistrict": "Amahlathi LM",
    "Facility": "Amabele Clinic",
    "gps_latitude": -32.6634,
    "gps_longitude": 27.5239
  },

  {
    "code": 455242,
    "Province": "Eastern Cape",
    "District": "Amathole DM",
    "Subdistrict": "Amahlathi LM",
    "Facility": "Burnshill Clinic",
    "gps_latitude": -32.7686,
    "gps_longitude": 27.055
  }
]