Display a rectangular bounding box (overlay) on custom Camera2 API so only the image inside the box is captured

I'm using the following code to capture an image using the custom Camera2 API. I am a beginner and I have no idea how to display a rectangular overlay on the camera preview. I did try the solutions available here, but I can't figure out how to fit it in my code.

I need to achieve something like this to capture A4 sheets.

Only the part of the image which is in the box must be captured and displayed in the next activity.

MainActivity

package com.example.customcamera;

import android.Manifest;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.ImageFormat;
import android.graphics.SurfaceTexture;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCaptureSession;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraDevice;
import android.hardware.camera2.CameraManager;
import android.hardware.camera2.CameraMetadata;
import android.hardware.camera2.CaptureRequest;
import android.hardware.camera2.TotalCaptureResult;
import android.hardware.camera2.params.StreamConfigurationMap;
import android.media.Image;
import android.media.ImageReader;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.HandlerThread;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.util.Size;
import android.util.SparseIntArray;
import android.view.Surface;
import android.view.TextureView;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.UUID;

public class MainActivity extends AppCompatActivity {

    private static final SparseIntArray ORIENTATIONS = new SparseIntArray();
    static
    {
        ORIENTATIONS.append(Surface.ROTATION_0, 90);
        ORIENTATIONS.append(Surface.ROTATION_90, 0);
        ORIENTATIONS.append(Surface.ROTATION_180, 270);
        ORIENTATIONS.append(Surface.ROTATION_270, 180);
    }

    TextureView textureView;
    private CameraDevice cameraDevice;
    private String cameraId;
    private Size imageDimensions;
    private CameraCaptureSession cameraCaptureSession;
    private CaptureRequest.Builder captureRequestBuilder;
    private ImageReader imageReader;
    private boolean flashSupported;
    private HandlerThread backgroundThread;
    private Handler backgroundHandler;


    CameraDevice.StateCallback stateCallback;
    File file;
    final int MY_PERMISSIONS_REQUEST_CAMERA=102;


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


        stateCallback = new CameraDevice.StateCallback() {
            @Override
            public void onOpened(@NonNull CameraDevice camera) {
                cameraDevice = camera;
                createCameraPreview();
            }

            @Override
            public void onDisconnected(@NonNull CameraDevice cameraDevice) {
                MainActivity.this.cameraDevice.close();
            }

            @Override
            public void onError(@NonNull CameraDevice cameraDevice, int i) {
                MainActivity.this.cameraDevice.close();
                MainActivity.this.cameraDevice = null;        // Change to global
            }
        };

        textureView = findViewById(R.id.textureView);
        textureView.setSurfaceTextureListener(textureListener);

        Button btn_camera = findViewById(R.id.btn_camera);
        btn_camera.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                takePicture();
            }
        });
    }

    public void takePicture()
    {
        if(cameraDevice == null)
            return;

        CameraManager cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);

        try
        {
            CameraCharacteristics cameraCharacteristics = cameraManager.getCameraCharacteristics(cameraDevice.getId());
            Size[] jpegSizes = null;

            if(cameraCharacteristics == null)
                jpegSizes = cameraCharacteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP).getOutputSizes(ImageFormat.JPEG);

            // Capture image with custom size
            int width = 640;
            int height = 480;

            if(jpegSizes != null && jpegSizes.length > 0)
            {
                width = jpegSizes[0].getWidth();
                height = jpegSizes[0].getHeight();
            }

            imageReader = ImageReader.newInstance(width, height, ImageFormat.JPEG, 1);
            final List<Surface> outputSurface = new ArrayList<>(2);
            outputSurface.add(imageReader.getSurface());
            outputSurface.add(new Surface(textureView.getSurfaceTexture()));

            final CaptureRequest.Builder captureBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
            captureBuilder.addTarget(imageReader.getSurface());
            captureBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);

            // Check orientation base on device
            int rotation = getWindowManager().getDefaultDisplay().getRotation();
            captureBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));

            ImageReader.OnImageAvailableListener readerListener = new ImageReader.OnImageAvailableListener() {
                @Override
                public void onImageAvailable(ImageReader imageReader) {

                    file = new File(Environment.getExternalStorageDirectory() + "/" + UUID.randomUUID().toString() + ".jpg");
                    Image image = null;

                    try
                    {
                        image = imageReader.acquireLatestImage();
                        ByteBuffer buffer = image.getPlanes()[0].getBuffer();
                        buffer.rewind();
                        byte[] bytes = new byte[buffer.capacity()];
                        buffer.get(bytes);
                        save(bytes);

                        startActivity(new Intent(MainActivity.this, ImageDisplay.class).putExtra("FILE", file.getPath()));
                    }

                    finally {
                        if(image != null)
                            image.close();
                    }
                }

                public void save(byte[] bytes)
                {
                    OutputStream outputStream = null;

                    try
                    {
                        outputStream = new FileOutputStream(file);
                        outputStream.write(bytes);
                    } catch (FileNotFoundException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    } finally {
                        if(outputStream == null) {
                            try {
                                outputStream.close();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            };

            imageReader.setOnImageAvailableListener(readerListener, backgroundHandler);

            final CameraCaptureSession.CaptureCallback captureCallback = new CameraCaptureSession.CaptureCallback() {
                @Override
                public void onCaptureCompleted(@NonNull CameraCaptureSession session, @NonNull CaptureRequest request, @NonNull TotalCaptureResult result) {
                    super.onCaptureCompleted(session, request, result);
                    Toast.makeText(MainActivity.this, "Saved", Toast.LENGTH_SHORT).show();
                    createCameraPreview();
                }
            };

            cameraDevice.createCaptureSession(outputSurface, new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(@NonNull CameraCaptureSession cameraCaptureSession) {
                    try {
                        cameraCaptureSession.capture(captureBuilder.build(), captureCallback, backgroundHandler);
                    } catch (CameraAccessException e) {
                        e.printStackTrace();
                    }
                }

                @Override
                public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {

                }
            }, backgroundHandler);
        }
        catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void createCameraPreview() {

        SurfaceTexture texture = textureView.getSurfaceTexture();
        assert texture != null;

        texture.setDefaultBufferSize(imageDimensions.getWidth(), imageDimensions.getHeight());
        Surface surface = new Surface(texture);
        try {
            captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            captureRequestBuilder.addTarget(surface);

            cameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(@NonNull CameraCaptureSession session) {
                    if(cameraDevice == null)
                        return;

                    cameraCaptureSession = session;
                    updatePreview();
                }

                @Override
                public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
                    Toast.makeText(MainActivity.this, "Changed", Toast.LENGTH_SHORT).show();
                }
            }, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private void updatePreview() {
        if(cameraDevice == null)
            Toast.makeText(MainActivity.this, "Error!", Toast.LENGTH_SHORT).show();

        captureRequestBuilder.set(CaptureRequest.CONTROL_MODE, CaptureRequest.CONTROL_MODE_AUTO);
        try {
            cameraCaptureSession.setRepeatingRequest(captureRequestBuilder.build(), null, backgroundHandler);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }

    }

    private void openCamera()
    {
        CameraManager cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try
        {
            cameraId = cameraManager.getCameraIdList()[0];
            CameraCharacteristics cameraCharacteristics = cameraManager.getCameraCharacteristics(cameraId);
            StreamConfigurationMap map = cameraCharacteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            assert map != null;
            imageDimensions = map.getOutputSizes(SurfaceTexture.class)[0];

            if (ContextCompat.checkSelfPermission(MainActivity.this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                // Permission to Camera is not granted, request for permission
                ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.CAMERA,
                                Manifest.permission.WRITE_EXTERNAL_STORAGE},  MY_PERMISSIONS_REQUEST_CAMERA);
                return;
            }

            cameraManager.openCamera(cameraId, stateCallback, null);
        }
        catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    TextureView.SurfaceTextureListener textureListener = new TextureView.SurfaceTextureListener() {
        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int i, int i1) {
            openCamera();
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int i, int i1) {

        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
            Log.e("Surfacetexturedestroyed", "called");
            if(cameraDevice != null)
            {
                Log.e("Camera not null", "make null");
                cameraDevice.close();
                cameraDevice = null;
            }
            return false;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {

        }
    };

    @Override
    protected void onResume() {
        super.onResume();

        startBackgroundThread();

        if(textureView.isAvailable())
            openCamera();
        else
            textureView.setSurfaceTextureListener(textureListener);
    }

    @Override
    protected void onPause() {
        stopBackgroundThread();
        super.onPause();
    }

    private void stopBackgroundThread() {
        backgroundThread.quitSafely();
        try {
            backgroundThread.join();
            backgroundThread = null;
            backgroundHandler = null;
        }
        catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    private void startBackgroundThread() {
        backgroundThread = new HandlerThread("Camera Background");
        backgroundThread.start();
        backgroundHandler = new Handler(backgroundThread.getLooper());
    }

    /**
     * Handler for handling the user event after requesting permission.
     */
    @Override
    public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults)
    {
        switch (requestCode)
        {
            case 102:     //MY_PERMISSIONS_REQUEST_CAMERA=102   Use Camera

                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0  && grantResults[0] == PackageManager.PERMISSION_GRANTED)
                {
                    // permission was granted, yay!
                    openCamera();
                }
                else
                {
                    // permission denied, boo!
                    Toast.makeText(this, "Permission to use device Camera denied! Cannot proceed ahead!", Toast.LENGTH_SHORT).show();
                    finish();
                }
                break;

            default: Toast.makeText(this, "Failed to handle permissions response!", Toast.LENGTH_SHORT).show();
        }
    }

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    tools:context=".MainActivity">

    <TextureView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:id="@+id/textureView"
        android:layout_alignParentTop="true"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Take Picture"
        android:textSize="30sp"
        android:id="@+id/btn_camera"
        android:layout_alignParentBottom="true"
        android:layout_margin="8dp"/>

</RelativeLayout>

ImageDisplay Activity

package com.example.customcamera;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Path;
import android.media.Image;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ImageView;

import java.io.File;

public class ImageDisplay extends AppCompatActivity {

    ImageView imageView;

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

        imageView = findViewById(R.id.imageView);

        String imgFile = getIntent().getStringExtra("FILE");

        Bitmap bitmap = BitmapFactory.decodeFile(imgFile);
        imageView.setImageBitmap(bitmap);
    }
}

image_display.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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"
    tools:context=".ImageDisplay">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</RelativeLayout>

from Display a rectangular bounding box (overlay) on custom Camera2 API so only the image inside the box is captured