Java Android; Como posso analisar um arquivo JSON local da pasta assets em um ListView

No momento, estou desenvolvendo um aplicativo de física que deve mostrar uma lista de fórmulas e até resolver algumas delas (o único problema é o ListView)

Este é o meu layout 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>

E esta é minha principal atividade

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;
    }
}

Na verdade, eu sei que posso fazer isso sem usar o JSON, mas preciso praticar mais a análise do JSON. A propósito, este é o 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"
    }
  ]
}

Eu tentei muitas coisas e até excluí todo o projeto para criar um novo :(

Como Faizan descreve em sua resposta aqui :

Antes de tudo, leia o arquivo Json do seu arquivo de atestados usando o código abaixo.

e então você pode simplesmente ler esse retorno de string por esta função 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;
}

e use esse método assim

    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 mais detalhes sobre o JSON, leia AQUI

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

O que você está fazendo

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

Então mude para

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

Para analisar

Acredito que você obtenha a string da pasta de testes.

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();
}

Com o Kotlin, tem esta função de extensão para ler o retorno do arquivo como string.

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

Analise a sequência de saída usando qualquer analisador JSON.

Método para ler o arquivo JSON da pasta Assets e retornar como um objeto de sequência.

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;

        }

Agora, para analisar dados em sua atividade: -

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

Código-fonte Como buscar o Local Json na pasta Assets

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;
    }

e depois...

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);

Apenas resumindo a resposta da @ libing com uma amostra que funcionou para mim.

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()}

Sem essa função de extensão, o mesmo pode ser alcançado usando BufferedReadere InputStreamReaderdesta maneira:

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

Se você estiver usando o Kotlin no Android, poderá criar a função de extensão .
As funções de extensão são definidas fora de qualquer classe - mas elas fazem referência ao nome da classe e podem ser usadas this. No nosso caso, usamos applicationContext.
Portanto, na classe Utility, você pode definir todas as funções de extensão.

Utility.kt

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

MainActivity.kt

Você pode definir a função privada para carregar dados JSON a partir da declaração da seguinte maneira:

 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)
    }
}

Você tem que passar facilityModelListna suaListView

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
}

No meu caso, a resposta JSON começa com 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
  }
]