Preview.java

// Very simple preview-only Camera2 example.

import android.view.*;
import android.hardware.camera2.*;
import android.os.*;
import android.content.*;
import android.content.pm.*;
import java.util.Arrays;
import android.util.Range;

public class Preview extends CameraDevice.StateCallback {
	Context ctx;
	SurfaceView sv;
	SurfaceHolder holder;

	HandlerThread thread;
	Handler handler;

	CameraDevice device;
	SessionCallback session_callback;
	CameraCaptureSession session;
	CaptureRequest.Builder builder;

	Range refresh_range;

	public Preview(Context ctx, SurfaceView sv) {
		this.ctx = ctx;
		this.sv = sv;

		this.thread = null;
		this.handler = null;

		this.session_callback = new SessionCallback();

		this.holder = sv.getHolder();
	}

	// Call inside your activity's onResume()
	public void start_camera_thread() {
		if (this.thread != null && this.handler != null)
			return;

		thread = new HandlerThread("Camera Background");
		thread.start();
		handler = new Handler(thread.getLooper());
	}

	// Call inside your activity's onPause()
	public void stop_camera_thread() {
		if (thread != null) {
			thread.quitSafely();
			try {
				thread.join();
			}
			catch (InterruptedException ex) {
				// Add error handling here
			}
		}

		thread = null;
		handler = null;
	}

	class SessionCallback extends CameraCaptureSession.StateCallback {
		@Override
		public void onConfigured(CameraCaptureSession ccs) {
			if (device == null)
				return;

			session = ccs;

			try {
				update_preview();
			}
			catch (CameraAccessException ex) {
				throw new RuntimeException(ex);
			}
		}
		public void onConfigureFailed(CameraCaptureSession ccs) {
			// Add error handling here
		}
	}

	// from CameraDevice.StateCallback
	@Override
	public void onOpened(CameraDevice camera) {
		device = camera;
		try {
			create_camera_preview();
		}
		catch (CameraAccessException ex) {
			throw new RuntimeException(ex);
		}
	}

	@Override
	public void onDisconnected(CameraDevice camera) {
		device.close();
	}

	@Override
	public void onError(CameraDevice camera, int error) {
		device.close();
		device = null;
	}

	void create_camera_preview() throws CameraAccessException {
		builder = device.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);

		var surface = holder.getSurface();
		builder.addTarget(surface);
		device.createCaptureSession(Arrays.asList(surface), this.session_callback, null);
	}

	void open_camera() throws CameraAccessException {
		var manager = (CameraManager)ctx.getSystemService(Context.CAMERA_SERVICE);

		var id = manager.getCameraIdList()[0];
		var character = manager.getCameraCharacteristics(id);

		// Get the list of acceptable frame rate ranges
		Range<Integer>[] refresh_ranges = character.get(CameraCharacteristics.CONTROL_AE_AVAILABLE_TARGET_FPS_RANGES);
		// This is where you may want to not be lazy and actually find an appropriate range
		this.refresh_range = refresh_ranges[0];

		manager.openCamera(id, this, null);
	}

	void update_preview() throws CameraAccessException {
		// Turn on automatic controls
		builder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);

		// Turn on automatic exposure
		builder.set(CaptureRequest.CONTROL_AE_MODE, CameraMetadata.CONTROL_AE_MODE_ON);

		// Set frame rate, and therefore shutter speed. Shutter speed affects brightness by increasing exposure time.
		builder.set(CaptureRequest.CONTROL_AE_TARGET_FPS_RANGE, this.refresh_range);

		session.setRepeatingRequest(builder.build(), null, handler);
	}

	void close_camera() {
		if (device != null) {
			device.close();
			device = null;
		}
	}
}