public class MainActivity extends AppCompatActivity {

    private int mCameraIndex = Camera.CameraInfo.CAMERA_FACING_FRONT;
    private Camera mCamera;
    private static final int SIZE_WIDTH = 960;
    private static final int SIZE_HEIGHT = 540;
    // 设置缓存帧数据容器，避免重复创建
    private byte[] mPreviewData = new byte[SIZE_WIDTH * SIZE_HEIGHT * 3 / 2];
    private ImageView mImageView;
    private boolean isShow = false;

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

    private void initView() {
        mImageView = findViewById(R.id.imageview);
    }

    @Override
    protected void onStart() {
        super.onStart();
        initCameara();
        setCallback();
    }

    @Override
    protected void onStop() {
        super.onStop();
        closeCamera();
    }

    public void clickButton(View view) {
        isShow = true;
    }

    /**
     * Camera初始化
     */
    private void initCameara() {
        mCamera = Camera.open(mCameraIndex);
        Camera.Parameters p = mCamera.getParameters();
        p.setPreviewFormat(ImageFormat.NV21);
        p.setPreviewSize(SIZE_WIDTH, SIZE_HEIGHT);
        p.setPictureFormat(ImageFormat.NV21);
        p.setPictureSize(SIZE_WIDTH, SIZE_HEIGHT);
        p.setZoom(0);
        p.setRotation(0);
        mCamera.setParameters(p);
    }

    /**
     * 开始监听回调，设置预览
     */
    private void setCallback() {
        try {
            // 主要是surfaceTexture获取预览数据，但不显示
            SurfaceTexture surfaceTexture = new SurfaceTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES);
            mCamera.setPreviewTexture(surfaceTexture);
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 设置 mCamera.addCallbackBuffer(mPreviewData) 后才会回调，旨在每处理完一帧数据回调一次
        mCamera.setPreviewCallbackWithBuffer(mPreviewCallback);
        mCamera.addCallbackBuffer(mPreviewData);
        mCamera.startPreview();
    }

    /**
     * 帧数据监听实现
     */
    private Camera.PreviewCallback mPreviewCallback = new Camera.PreviewCallback() {
        @Override
        public void onPreviewFrame(byte[] data, Camera camera) {
            // 在此处处理当前帧数据，并设置下一帧回调
            mCamera.addCallbackBuffer(mPreviewData);
            if (isShow) {
                showPic(mPreviewData);
                isShow = false;
            }
        }
    };

    /**
     * 显示图片
     */
    private void showPic(byte[] data){
        try {
            YuvImage  image = new YuvImage(data, ImageFormat.NV21,SIZE_WIDTH, SIZE_HEIGHT, null);
            if (image != null) {
                ByteArrayOutputStream stream = new ByteArrayOutputStream();
                image.compressToJpeg(new Rect(0, 0, SIZE_WIDTH, SIZE_HEIGHT), 100, stream);
                Bitmap bm = BitmapFactory.decodeByteArray(stream.toByteArray(), 0, stream.size());
                stream.close();
                bm = Util.convertBmp(bm);
                mImageView.setImageBitmap(bm);
            }
        } catch (Exception e) {
        }
    }

    /**
     * 关闭相机
     */
    private void closeCamera() {
        mCamera.stopPreview();
        mCamera.setPreviewCallbackWithBuffer(null);
        mCamera.release();
        mCamera = null;
    }
}