在安卓设备上，把文件读出成String，在写回去，文件大小不对了，打开显示乱码了。指定一下编码格式就解决了。代码如下：

 private static final String destPath = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).getAbsolutePath();
 private static final String srcPath = destPath+File.separator+"bg_device_detail_nvr.jpg";
 public static final String receivePath = destPath+File.separator+"nvr.jpg";

    private void testFile(){
        getPermission();
        BufferedInputStream bis = null;
        ByteArrayOutputStream baos = null;

        BufferedOutputStream bos = null;
        ByteArrayInputStream bais = null;
        try {

            if (!new File(srcPath).exists()){
                Toast.makeText(this,"文件不存在！",Toast.LENGTH_SHORT).show();
                return;
            }

            bis = new BufferedInputStream(new FileInputStream(srcPath));
            baos = new ByteArrayOutputStream();

            bos = new BufferedOutputStream(new FileOutputStream(receivePath));

            byte[] buffer = new byte[1024];
            int len = -1;
            while ((len = bis.read(buffer))!=-1){
                baos.write(buffer, 0, len);
            }
            byte[] bb= baos.toByteArray();
            String temp = new String(bb, StandardCharsets.ISO_8859_1); //指定编码后就解决乱码问题了
            byte[] result = temp.getBytes(StandardCharsets.ISO_8859_1);

            bos.write(result, 0, result.length);

            Toast.makeText(this,"完成", Toast.LENGTH_SHORT).show();

        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            try {
                if (null != baos) {
                    baos.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }

            try {
                if (null != bis) {
                    bis.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }


            try {
                if (null != bais){
                    bais.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (null != bos){
                try {
                    bos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

记录一下