Android - JSON Parser

JSON Parser

JSON stands for JavaScript Object Notation.It is an independent data exchange format and is the best alternative for XML. 

This chapter explains how to parse the JSON file and extract necessary information from it.

Android provides four different classes to manipulate JSON data. 

These classes are JSONArray,JSONObject,JSONStringer and JSONTokenizer.

The first step is to identify the fields in the JSON data . In the JSON given below. 

For example: 

http://demo.codeofaninja.com/tutorials/json-example-with-php/index.php

{"Users":

[

{"firstname":"Mike","lastname":"Dalisay","username":"mike143"},

{"firstname":"Jemski","lastname":"Panlilios","username":"jemboy09"},

{"firstname":"Darwin","lastname":"Dalisay","username":"dada08"},

{"firstname":"Jaylord","lastname":"Bitamug","username":"jayjay"},

{"firstname":"Justine","lastname":"Bongola","username":"jaja"},

{"firstname":"Jun","lastname":"Sabayton","username":"jun"},

{"firstname":"Lourd","lastname":"De Veyra","username":"lourd"},

{"firstname":"Asi","lastname":"Taulava","username":"asi"},

{"firstname":"James","lastname":"Yap","username":"james"},

{"firstname":"Chris","lastname":"Tiu","username":"chris"},

{"firstname":"xxxrrr","lastname":"xxxrrr","username":"xxrrr"}

]}

JSON - Elements:

An JSON file consist of many components. Here is the table defining the components of an JSON file and their description −

 

	Component & description

	Array([) In a JSON file , square bracket ([) represents a JSON array
	Objects({) In a JSON file, curly bracket ({) represents a JSON object
	Key A JSON object contains a key that is just a string. Pairs of key/value make up a JSON object
	Value Each key has a value that could be string , integer or double e.t.c JSON - Parsing: For parsing a JSON object, we will create an object of class JSONObject and specify a string containing JSON data to it. Its syntax is: String s; JSONObject jsonObject=new JSONObject(s); JSONArray jsonArray=jsonObject.getJSONArray("Users");       The last step is to parse the JSON. An JSON file consist of different object with different key/value pair e.t.c.  So JSONObject has a separate function for parsing each of the component of JSON file. Its syntax is given below: jsonArray.getJSONObject().getString("firstname"); jsonArray.getJSONObject().getString("username"); jsonArray.getJSONObject().getString("lastname")     The method getJSONObject returns the JSON object. The method getString returns the string value of the specified key. Apart from the these methods , there are other methods provided by this class for better parsing JSON files. These methods are listed below −   Method & description:

	get(String name) This method just Returns the value but in the form of Object type
	getBoolean(String name) This method returns the boolean value specified by the key
	getDouble(String name) This method returns the double value specified by the key
	getInt(String name) This method returns the integer value specified by the key
	getLong(String name) This method returns the long value specified by the key
	length() This method returns the number of name/value mappings in this object..
	names() This method returns an array containing the string names in this object. Example To experiment with this example , you can run this on an actual device or in an emulator. Here, I have Student details json and i download all student details using Asynctask for that i create pojo class and i put in to the listview for that i create Adapter class.In manifest need INTERNET Permission. MainActivity: package com.example.root.studentjson; import android.support.v7.app.ActionBarActivity; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.Button; import android.widget.ListView; public class MainActivity extends ActionBarActivity { Button getlist_bt; ListView list; MyAsync async; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); getlist_bt=(Button)findViewById(R.id.button); list=(ListView)findViewById(R.id.listView); getlist_bt.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { async= new MyAsync(MainActivity.this,list); async.execute("http://demo.codeofaninja.com/tutorials/json-example-with-php/index.php"); } }); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.menu_main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); //noinspection SimplifiableIfStatement if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } } MyAdapter: package com.example.root.studentjson; import android.content.Context; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.TextView; import java.util.ArrayList; /** * Created by root on 9/12/15. */public class MyAdapter extends BaseAdapter { Context c; ArrayList<Users> al; LayoutInflater layoutInflater; public MyAdapter(Context c, ArrayList<Users> al) { this.c = c; this.al = al; layoutInflater=LayoutInflater.from(c); } @Override public int getCount() { return al.size(); } @Override public Object getItem(int position) { return null; } @Override public long getItemId(int position) { return 0; } @Override public View getView(int position, View convertView, ViewGroup parent) { if(convertView==null) { convertView=layoutInflater.inflate(R.layout.item_list,parent,false); } TextView firstname_tv=(TextView)convertView.findViewById(R.id.firstname); TextView username_tv=(TextView)convertView.findViewById(R.id.username); TextView lastname_tv=(TextView)convertView.findViewById(R.id.lastname); firstname_tv.setText(al.get(position).getFirstname()); username_tv.setText(al.get(position).getUsername()); lastname_tv.setText(al.get(position).getLastname()); return convertView; } } MyAsync:   package com.example.root.studentjson; import android.app.ProgressDialog; import android.content.Context; import android.os.AsyncTask; import android.widget.ListView; import org.json.JSONArray; import org.json.JSONObject; import java.io.BufferedReader; import java.io.InputStream; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL; import java.util.ArrayList; /** * Created by root on 9/12/15. */public class MyAsync extends AsyncTask<String,String ,String > { Context c; ListView list; MyAdapter adapter; ProgressDialog pd; public MyAsync(Context c, ListView list) { this.c = c; this.list = list; } @Override protected String doInBackground(String... params) { try { URL url=new URL(params[0]); HttpURLConnection httpURLConnection=(HttpURLConnection)url.openConnection(); httpURLConnection.connect(); InputStream inputStream=httpURLConnection.getInputStream(); BufferedReader br = new BufferedReader(new InputStreamReader(inputStream)); StringBuilder sb = new StringBuilder(); String line; while ((line = br.readLine()) != null) { sb.append(line+"\n"); } br.close(); return sb.toString(); }catch (Exception e){ } return null; } @Override protected void onPostExecute(String s) { super.onPostExecute(s); try { ArrayList<Users> arrayList=new ArrayList<>(); JSONObject jsonObject=new JSONObject(s); JSONArray jsonArray=jsonObject.getJSONArray("Users"); for (int i=0;i<jsonArray.length();i++){ Users users=new Users(jsonArray.getJSONObject(i).getString("firstname"),jsonArray.getJSONObject(i).getString("username"),jsonArray.getJSONObject(i).getString("lastname")); arrayList.add(users); } adapter=new MyAdapter(c,arrayList); list.setAdapter(adapter); pd.dismiss(); }catch (Exception e){ } } @Override protected void onPreExecute() { pd=new ProgressDialog(c); pd.setMessage("downloading json"); pd.show(); super.onPreExecute(); } @Override protected void onProgressUpdate(String... values) { super.onProgressUpdate(values); } }   Users:   package com.example.root.studentjson; /** * Created by root on 9/12/15. */public class Users { String firstname,username,lastname; public Users(String firstname, String username, String lastname) { this.firstname = firstname; this.username = username; this.lastname = lastname; } public String getFirstname() { return firstname; } public void setFirstname(String firstname) { this.firstname = firstname; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getLastname() { return lastname; } public void setLastname(String lastname) { this.lastname = lastname; } } Manifest:   <?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.root.studentjson" > <uses-permission android:name="android.permission.INTERNET"> </uses-permission> <application android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name=".MainActivity" android:label="@string/app_name" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest> Can you run this code, you will get student details list show in listview.