AsyncTask in Android

The AsyncTask (Asynchronous Task) feature in Android makes it possible to run a task in the background and synchronize with our main thread again. At least one method in this class will be overridden i.e. doInBackground(Params), and most commonly onPostExecute(Result).

AysncTask workflow

We will learn about how to run networking operations on a different thread and how to use Androids networking client to grab data from a network. Finally, we will learn how to parse the results in order to extract our specific value from an information.

For our example, we are going to pull json from a movie API and set the result into textview.

Movie JSON link

https://www.techstackguru.com/json-files/avengers-movie.json

Postman tool to check our API calls

Listed below are the contents of the modified main activity file.

MainActivity.java


package com.example.techstackguru;

import androidx.appcompat.app.AppCompatActivity;

import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.TextView;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    TextView textView;

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

        textView = findViewById(R.id.tv1);

        new GetMovie().execute();
    }

    private class GetMovie extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

    @Override
    protected Void doInBackground(Void... arg0) {
          String apiUrl = "https://www.techstackguru.com/json-files/avengers-movie.json";

          try {
              URL url = new URL(apiUrl);
              HttpURLConnection  urlConnection = (HttpURLConnection) url.openConnection();
              InputStream stream = new BufferedInputStream(urlConnection.getInputStream());

              BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(stream));
              StringBuilder builder = new StringBuilder();

              String inputString;
              while ((inputString = bufferedReader.readLine()) != null) {
                  builder.append(inputString);
              }

              JSONObject object = new JSONObject(builder.toString());
              String name = object.getString("movieName");
              textView.setText(name);
              urlConnection.disconnect();

          } catch (IOException | JSONException e) {
              e.printStackTrace();
          }
          
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        super.onPostExecute(result);
    }
  }
}

Add below code in your XML

activity_main.xml


<?xml version="1.0" encoding="utf-8"?>
<androidx.appcompat.widget.LinearLayoutCompat xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <TextView
        android:id="@+id/tv1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:textSize="26sp"
        android:gravity="center"
        android:text="asadad"
        android:ems="10" />

</androidx.appcompat.widget.LinearLayoutCompat>

Give internet permission

AndroidManifest.xml


<uses-permission android:name="android.permission.INTERNET" />

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