安卓5，相机2只使用闪光灯

https://github.com/pinguo-yuyidong/Camera2/blob/master/app/src/main/java/us/yydcdut/androidltest/otheractivity/FlashActivity.java
在这里，您不需要预览即可打开闪光灯。

只需使用以下类即可在Android L中打开/关闭手电筒，

public class FlashLightUtilForL {
    private CameraCaptureSession mSession;
    private CaptureRequest.Builder mBuilder;
    private CameraDevice mCameraDevice;
    private CameraManager mCameraManager;

    public FlashLightUtilForL(Context context) {
        try {
            mCameraManager = (CameraManager) context.getSystemService(Context.CAMERA_SERVICE);
            //here to judge if flash is available
            CameraCharacteristics cameraCharacteristics = mCameraManager.getCameraCharacteristics("0");
            boolean flashAvailable = cameraCharacteristics.get(CameraCharacteristics.FLASH_INFO_AVAILABLE);
            if (flashAvailable) {
                mCameraManager.openCamera("0", new MyCameraDeviceStateCallback(), null);
            } else {
                //todo: throw Exception
            }
            //mCameraManager.openCamera("0", new MyCameraDeviceStateCallback(), null);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    class MyCameraDeviceStateCallback extends CameraDevice.StateCallback {

        @Override
        public void onOpened(CameraDevice camera) {
            mCameraDevice = camera;
            //get builder
            try {
                mBuilder = camera.createCaptureRequest(CameraDevice.TEMPLATE_MANUAL);
                //flash on, default is on
                mBuilder.set(CaptureRequest.CONTROL_AE_MODE, CameraMetadata.CONTROL_AF_MODE_AUTO);
                mBuilder.set(CaptureRequest.FLASH_MODE, CameraMetadata.FLASH_MODE_TORCH);
                List<Surface> list = new ArrayList<Surface>();
                SurfaceTexture mSurfaceTexture = new SurfaceTexture(1);
                Size size = getSmallestSize(mCameraDevice.getId());
                mSurfaceTexture.setDefaultBufferSize(size.getWidth(), size.getHeight());
                Surface mSurface = new Surface(mSurfaceTexture);
                list.add(mSurface);
                mBuilder.addTarget(mSurface);
                camera.createCaptureSession(list, new MyCameraCaptureSessionStateCallback(), null);
            } catch (CameraAccessException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onDisconnected(CameraDevice camera) {

        }

        @Override
        public void onError(CameraDevice camera, int error) {

        }
    }

    private Size getSmallestSize(String cameraId) throws CameraAccessException {
        Size[] outputSizes = mCameraManager.getCameraCharacteristics(cameraId)
                .get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)
                .getOutputSizes(SurfaceTexture.class);
        if (outputSizes == null || outputSizes.length == 0) {
            throw new IllegalStateException(
                    "Camera " + cameraId + "doesn't support any outputSize.");
        }
        Size chosen = outputSizes[0];
        for (Size s : outputSizes) {
            if (chosen.getWidth() >= s.getWidth() && chosen.getHeight() >= s.getHeight()) {
                chosen = s;
            }
        }
        return chosen;
    }

    /**
     * session callback
     */
    class MyCameraCaptureSessionStateCallback extends CameraCaptureSession.StateCallback {

        @Override
        public void onConfigured(CameraCaptureSession session) {
            mSession = session;
            try {
                mSession.setRepeatingRequest(mBuilder.build(), null, null);
            } catch (CameraAccessException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onConfigureFailed(CameraCaptureSession session) {

        }
    }

    public void turnOnFlashLight() {
        try {
            mBuilder.set(CaptureRequest.FLASH_MODE, CameraMetadata.FLASH_MODE_TORCH);
            mSession.setRepeatingRequest(mBuilder.build(), null, null);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void turnOffFlashLight() {
        try {
            mBuilder.set(CaptureRequest.FLASH_MODE, CameraMetadata.FLASH_MODE_OFF);
            mSession.setRepeatingRequest(mBuilder.build(), null, null);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void close() {
        if (mCameraDevice == null || mSession == null) {
            return;
        }
        mSession.close();
        mCameraDevice.close();
        mCameraDevice = null;
        mSession = null;
    }
}