用java写一个camera api2的拍照demo

好的，以下是一个简单的Camera2 API拍照的demo:

1. 在AndroidManifest.xml文件中添加相机权限:

<uses-feature android:name="android.hardware.camera" />
<uses-permission android:name="android.permission.CAMERA" />

2. 在布局文件中添加一个TextureView用于预览相机画面:

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

3. 在Activity中定义相机相关变量:

private CameraManager cameraManager;
private String cameraId;
private CameraDevice cameraDevice;
private Size previewSize;
private CaptureRequest.Builder previewBuilder;
private CameraCaptureSession previewSession;
private ImageReader imageReader;

4. 在Activity中初始化相机:

private void initCamera() {
    cameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
    try {
        for (String cameraId : cameraManager.getCameraIdList()) {
            CameraCharacteristics characteristics = cameraManager.getCameraCharacteristics(cameraId);
            if (characteristics.get(CameraCharacteristics.LENS_FACING) == CameraCharacteristics.LENS_FACING_BACK) {
                this.cameraId = cameraId;
                break;
            }
        }
        StreamConfigurationMap map = cameraManager.getCameraCharacteristics(cameraId)
                .get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
        previewSize = map.getOutputSizes(SurfaceTexture.class)[0];
        imageReader = ImageReader.newInstance(previewSize.getWidth(), previewSize.getHeight(), ImageFormat.JPEG, 1);
        imageReader.setOnImageAvailableListener(imageReaderListener, null);
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED) {
            return;
        }
        cameraManager.openCamera(cameraId, cameraStateCallback, null);
    } catch (CameraAccessException e) {
        e.printStackTrace();
    }
}

5. 在Activity中实现相机状态回调:

private CameraDevice.StateCallback cameraStateCallback = new CameraDevice.StateCallback() {
    @Override
    public void onOpened(CameraDevice camera) {
        cameraDevice = camera;
        try {
            SurfaceTexture texture = textureView.getSurfaceTexture();
            texture.setDefaultBufferSize(previewSize.getWidth(), previewSize.getHeight());
            Surface surface = new Surface(texture);
            previewBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            previewBuilder.addTarget(surface);
            cameraDevice.createCaptureSession(Arrays.asList(surface, imageReader.getSurface()), captureStateCallback, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onDisconnected(CameraDevice camera) {
        cameraDevice.close();
        cameraDevice = null;
    }

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

6. 在Activity中实现相机捕获状态回调:

private CameraCaptureSession.StateCallback captureStateCallback = new CameraCaptureSession.StateCallback() {
    @Override
    public void onConfigured(CameraCaptureSession session) {
        previewSession = session;
        try {
            previewBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
            previewSession.setRepeatingRequest(previewBuilder.build(), null, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onConfigureFailed(CameraCaptureSession session) {

    }
};

7. 在Activity中实现ImageReader的回调方法，用于保存图片:

private ImageReader.OnImageAvailableListener imageReaderListener = new ImageReader.OnImageAvailableListener() {
    @Override
    public void onImageAvailable(ImageReader reader) {
        Image image = reader.acquireNextImage();
        ByteBuffer buffer = image.getPlanes()[0].getBuffer();
        byte[] data = new byte[buffer.remaining()];
        buffer.get(data);
        saveImage(data);
        image.close();
    }
};

8. 在Activity中添加保存图片的方法:

private void saveImage(byte[] data) {
    try {
        File file = new File(getExternalFilesDir(null), "photo.jpg");
        FileOutputStream fos = new FileOutputStream(file);
        fos.write(data);
        fos.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

9. 最后在Activity中调用initCamera()方法，即可启动相机预览并拍照:

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

@Override
protected void onPause() {
    super.onPause();
    if (cameraDevice != null) {
        cameraDevice.close();
        cameraDevice = null;
    }
}

以上是一个简单的Camera2 API拍照的demo，希望能对您有所帮助。