JSON Parsing in Android

Last Updated : 23 Oct, 2020

JSON (JavaScript Object Notation) is a straightforward data exchange format to interchange the server’s data, and it is a better alternative for XML. This is because JSON is a lightweight and structured language. Android supports all the JSON classes such as JSONStringer, JSONObject, JSONArray, and all other forms to parse the JSON data and fetch the required information by the program. JSON’s main advantage is that it is a language-independent, and the JSON object will contain data like a key/value pair. In general, JSON nodes will start with a square bracket ([) or with a curly bracket ({). The square and curly bracket’s primary difference is that the square bracket ([) represents the beginning of a JSONArray node. Whereas, the curly bracket ({) represents a JSONObject. So one needs to call the appropriate method to get the data. Sometimes JSON data start with [. We then need to use the getJSONArray() method to get the data. Similarly, if it starts with {, then we need to use the getJSONobject() method. The syntax of the JSON file is as following:

{ 
"Name": "GeeksforGeeks", 
"Estd": 2009, 
"age": 10, 
"address": { 
    "buildingAddress": "5th & 6th Floor Royal Kapsons, A- 118", 
    "city": "Sector- 136, Noida", 
    "state": "Uttar Pradesh (201305)", 
    "postalCode": "201305"
},

In this article, we are going to parse a JSON file in Android. Note that we are going to implement this project using the Kotlin language.

Step by Step Implementation

To parse a JSON file in Android, follow the following steps:

Step 1: Create a New Project

To create a new project in Android Studio please refer to How to Create/Start a New Project in Android Studio. Note that select Kotlin as the programming language.

Step 2: Working with the activity_main.xml file

Go to the activity_main.xml file which represents the UI of the application. Create a ListView as shown. Below is the code for the activity_main.xml file.

XML

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" > 
  
    <!--This listView will display the list items-->
    <ListView
        android:id="@+id/user_list"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:dividerHeight="1dp" /> 
    
</LinearLayout>

Step 3: Create another layout resource file

Go to app > res > layout > right-click > New > Layout Resource File and create another layout list_row.xml to show the data in the ListView. Below is the code for the list_row.xml file.

XML

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:padding="5dip"> 
  
    <!--TextView to display the name-->
    <TextView
        android:id="@+id/name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="17dp"
        android:textStyle="bold" /> 
  
    <!--TextView to display the designation-->
    <TextView
        android:id="@+id/designation"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/name"
        android:layout_marginTop="7dp"
        android:textColor="#343434"
        android:textSize="14dp" /> 
  
    <!--TextView to display the location-->
    <TextView
        android:id="@+id/location"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/designation"
        android:layout_alignBottom="@+id/designation"
        android:layout_alignParentRight="true"
        android:textColor="#343434"
        android:textSize="14dp" /> 
</RelativeLayout>

Step 4: Working with the MainActivity.kt file

Go to the MainActivity.kt file, and refer to the following code. Below is the code for the MainActivity.kt file. Comments are added inside the code to understand the code in more detail.

Kotlin

import android.os.Bundle 
import android.util.Log 
import android.widget.ListAdapter 
import android.widget.ListView 
import android.widget.SimpleAdapter 
import androidx.appcompat.app.AppCompatActivity 
import org.json.JSONException 
import org.json.JSONObject 
import java.util.* 
  
class MainActivity : AppCompatActivity() { 
    override fun onCreate(savedInstanceState: Bundle?) { 
        super.onCreate(savedInstanceState) 
        setContentView(R.layout.activity_main) 
  
        // private string declare in the latter section of the program 
        val jsonStr = listData 
        try { 
  
            // Create a userList string hashmap arraylist 
            val userList = ArrayList<HashMap<String, String?>>() 
  
            // Declaring the listView from the layout file 
            val lv = findViewById<ListView>(R.id.user_list) 
  
            // Initializing the JSON object and extracting the information 
            val jObj = JSONObject(jsonStr) 
            val jsonArry = jObj.getJSONArray("users") 
            for (i in 0 until jsonArry.length()) { 
                val user = HashMap<String, String?>() 
                val obj = jsonArry.getJSONObject(i) 
                user["name"] = obj.getString("name") 
                user["designation"] = obj.getString("designation") 
                user["location"] = obj.getString("location") 
                userList.add(user) 
            } 
  
            // ListAdapter to broadcast the information to the list elements 
            val adapter: ListAdapter = SimpleAdapter( 
                this, userList, R.layout.list_row, 
                arrayOf("name", "designation", "location"), intArrayOf( 
                    R.id.name, 
                    R.id.designation, R.id.location 
                ) 
            ) 
            lv.adapter = adapter 
        } catch (ex: JSONException) { 
            Log.e("JsonParser Example", "unexpected JSON exception", ex) 
        } 
    } 
  
  
    // JSON object in the form of input stream 
    private val listData: String 
        get() = ("{ \"users\" :[" + 
                "{\"name\":\"Ace\",\"designation\":\"Engineer\",\"location\":\"New York\"}" + 
                ",{\"name\":\"Tom\",\"designation\":\"Director\",\"location\":\"Chicago\"}" + 
                ",{\"name\":\"Tim\",\"designation\":\"Charted Accountant\",\"location\":\"Sunnyvale\"}] }") 
}