Kotlin Android JSON Parsing using URL

JSON refers to JavaScript Object Notation, and it is a programming language. JSON is used to parse the data between the server and the client. It is minimal, textual and a subset of JavaScript. It is the alternative to XML parsing.

The advantage of JSON over XML

JSON is faster and easier than XML for AJAX applications.
Unlike XML, it is shorter and quicker to read and write.
It uses an array.

JSON Object

A JSON object contains key/value pairs like a map. The keys are strings and the values are the JSON types. A comma separates keys and values (,). The curly brace {} represents the JSON object.

Kotlin JSON Parsing using URL Example

In this example, we parse the JSON data from URL and bind them into a ListView. The JSON data contains the "id" "name" "email".

JSON data index.html

Create a JSON file index.html.

{"info":[
		{"name":"Ajay","id":"111","email":"ajay@gmail.com"},
		{"name":"John","id":"112","email":"john@gmail.com"},
		{"name":"Rahul","id":"113","email":"rahul@gmail.com"},
		{"name":"Maich","id":"114","email":"maich@gmail.com"},
		{"name":"Vikash","id":"115","email":"vikash@gmail.com"},
		{"name":"Mayank","id":"116","email":"mayank@gmail.com"},
		{"name":"Prem","id":"117","email":"prem@gmail.com"},
		{"name":"Chandan","id":"118","email":"chandan@gmail.com"},
		{"name":"Soham","id":"119","email":"soham@gmail.com"},
		{"name":"Mukesh","id":"120","email":"mukesh@gmail.com"},
		{"name":"Ajad","id":"121","email":"ajad@gmail.com"}
		]
}

While executing the JSON file (index.html) looks like as:

activity_main.xml

Add the ListView in the activity_main.xml layout file.

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="example.javatpoint.com.kotlinjsonparsing.MainActivity">

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

    </ListView>

</android.support.constraint.ConstraintLayout>

build.gradle

Add the following okhttp dependency in the build.gradle file.

Model.kt

Create a data model class Model.kt which includes the information String "id", String "name" and String "email".

package example.javatpoint.com.kotlinjsonparsing

public class Model{
    lateinit var id:String
    lateinit var name:String
    lateinit var email:String

    constructor(id: String,name:String,email:String) {
        this.id = id
        this.name = name
        this.email = email
    }

    constructor()
}

adapter_layout.xml

Create an adapter_layout.xml file in the layout directory which contains the row items for ListView.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/linearLayout"
    android:padding="5dp"
    android:orientation="vertical">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tvId"
        android:layout_margin="5dp"
        android:textSize="16dp"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tvName"
        android:textSize="16dp"
        android:layout_margin="5dp"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/tvEmail"
        android:layout_margin="5dp"
        android:textSize="16dp"/>

</LinearLayout>

CustomAdapter.kt

Create a custom adapter class CustomAdapter.kt and extend BaseAdapter to handle the custom ListView.

package example.javatpoint.com.kotlinjsonparsing

import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.BaseAdapter
import android.widget.LinearLayout
import android.widget.TextView

class CustomAdapter(context: Context,arrayListDetails:ArrayList<Model>) : BaseAdapter(){

    private val layoutInflater: LayoutInflater
    private val arrayListDetails:ArrayList<Model>

    init {
        this.layoutInflater = LayoutInflater.from(context)
        this.arrayListDetails=arrayListDetails
    }

    override fun getCount(): Int {
        return arrayListDetails.size
    }

    override fun getItem(position: Int): Any {
        return arrayListDetails.get(position)
    }

    override fun getItemId(position: Int): Long {
        return position.toLong()
    }

    override fun getView(position: Int, convertView: View?, parent: ViewGroup): View? {
        val view: View?
        val listRowHolder: ListRowHolder
        if (convertView == null) {
            view = this.layoutInflater.inflate(R.layout.adapter_layout, parent, false)
            listRowHolder = ListRowHolder(view)
            view.tag = listRowHolder
        } else {
            view = convertView
            listRowHolder = view.tag as ListRowHolder
        }

        listRowHolder.tvName.text = arrayListDetails.get(position).name
        listRowHolder.tvEmail.text = arrayListDetails.get(position).email
        listRowHolder.tvId.text = arrayListDetails.get(position).id
        return view
    }
}

private class ListRowHolder(row: View?) {
    public val tvName: TextView
    public val tvEmail: TextView
    public val tvId: TextView
    public val linearLayout: LinearLayout

    init {
        this.tvId = row?.findViewById<TextView>(R.id.tvId) as TextView
        this.tvName = row?.findViewById<TextView>(R.id.tvName) as TextView
        this.tvEmail = row?.findViewById<TextView>(R.id.tvEmail) as TextView
        this.linearLayout = row?.findViewById<LinearLayout>(R.id.linearLayout) as LinearLayout
    }
}

MainActivity.kt

Add the following code in MainActivity.kt class file. This class read the JSON data in the form of a JSON object. Using the JSON object, we read the JSON array data. The JSON data are bind in ArrayList.

package example.javatpoint.com.kotlinjsonparsing

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.ListView
import android.widget.ProgressBar
import okhttp3.*
import org.json.JSONArray
import org.json.JSONObject
import java.io.IOException
import kotlin.collections.ArrayList

class MainActivity : AppCompatActivity() {
    lateinit var progress:ProgressBar
    lateinit var listView_details: ListView
    var arrayList_details:ArrayList<Model> = ArrayList();
    //OkHttpClient creates connection pool between client and server
    val client = OkHttpClient()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        progress = findViewById(R.id.progressBar)
        progress.visibility = View.VISIBLE
        listView_details = findViewById<ListView>(R.id.listView) as ListView
        run("http://10.0.0.7:8080/jsondata/index.html")
    }

    fun run(url: String) {
        progress.visibility = View.VISIBLE
        val request = Request.Builder()
                .url(url)
                .build()

        client.newCall(request).enqueue(object : Callback {
            override fun onFailure(call: Call, e: IOException) {
                progress.visibility = View.GONE
            }

            override fun onResponse(call: Call, response: Response) {
                var str_response = response.body()!!.string()
                //creating json object
                val json_contact:JSONObject = JSONObject(str_response)
                //creating json array
                var jsonarray_info:JSONArray= json_contact.getJSONArray("info")
                var i:Int = 0
                var size:Int = jsonarray_info.length()
                arrayList_details= ArrayList();
                for (i in 0.. size-1) {
                    var json_objectdetail:JSONObject=jsonarray_info.getJSONObject(i)
                    var model:Model= Model();
                    model.id=json_objectdetail.getString("id")
                    model.name=json_objectdetail.getString("name")
                    model.email=json_objectdetail.getString("email")
                    arrayList_details.add(model)
                }

                runOnUiThread {
                    //stuff that updates ui
                    val obj_adapter : CustomAdapter
                    obj_adapter = CustomAdapter(applicationContext,arrayList_details)
                    listView_details.adapter=obj_adapter
                }
                progress.visibility = View.GONE
            }
        })
    }
}