How to convert java bitmap to byte array In android?

This example demonstrates how do I convert java bitmap to byte array in android.

Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.xml.

<RelativeLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:id="@+id/rl"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:padding="10dp"
   tools:context=".MainActivity">
   <Button
      android:id="@+id/button"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerHorizontal="true"
      android:layout_marginTop="25sp"
      android:text="Convert Bitmap To Byte Array" />
   <ImageView
      android:id="@+id/ivSource"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@id/button" />
   <ImageView
      android:id="@+id/ivCompressed"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@id/button"
      android:layout_toRightOf="@id/ivSource" />
</RelativeLayout>

Step 3 − Add the following code to src/MainActivity.java

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
public class MainActivity extends AppCompatActivity {
   Button button;
   ImageView ivSource, ivCompressed;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      button = findViewById(R.id.button);
      ivCompressed = findViewById(R.id.ivCompressed);
      ivSource = findViewById(R.id.ivSource);
      button.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            try {
               InputStream inputStream = getAssets().open("image.png");
               Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
               ivSource.setImageBitmap(bitmap);
               ByteArrayOutputStream stream = new ByteArrayOutputStream();
               bitmap.compress(Bitmap.CompressFormat.JPEG,80,stream);
               byte[] byteArray = stream.toByteArray();
               Bitmap compressedBitmap = BitmapFactory.decodeByteArray(byteArray,0,byteArray.length);
               ivCompressed.setImageBitmap(compressedBitmap);
               Toast.makeText(getApplicationContext(),
               "ByteArray created..",
               Toast.LENGTH_SHORT).show();
            } catch (IOException e) {
               e.printStackTrace();
            }
         }
      });
   }
}

Step 4 − Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest
   xmlns:android="http://schemas.android.com/apk/res/android"
   package="app.com.sample">
   <uses-permission
      android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action
               android:name="android.intent.action.MAIN" />
            <category
               android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen −