获取 Jpg图片的像素数

/**

     * 获取 Jpg图片的像素数

     * @param is

     * @return

     */

    private static long getJpgPixes(InputStream is)

    {

        int w = 0;

        int h = 0;

        int b = 0;

        try

        {

            while ( (b = is.read()) != -1)

            {

                if (b == 0xff)

                {

                    b = is.read();

                    if (b >= 0xc0 && b <= 0xc3)

                    {   

                        is.skip(3);//跳过3字节

                        h = (is.read() << 8) | (is.read());

                        w = (is.read() << 8) | (is.read());

                        return w * h;

                    }

                    else if (b != 0 && b != 0xd9 && b !=0xd8)

                    {

                        int length = (is.read() << 8) | (is.read());

                        is.skip(length - 2);

                    }

                    else if (b == -1)

                    {

                        break;

                    }

                }

            }

            return -1;

        }

        catch (Exception e) 

        {

            e.printStackTrace();

        }

        return -1;

    }